No roof survives a violent tornado. That is not the useful question.
Steep-slope roofs · single-family and small multifamily
The useful question is what the roof does in the storm you are far more likely to get: a 70 mph straight-line gust, a derecho, or the weak outer edge of a tornado. There, attachment decides everything.
Can a roof be built to survive a tornado?
No covering on the market survives the core of a violent tornado, and any product sold on that promise is selling something. What roofing choices genuinely change is performance in straight-line wind, derechos, and the weak periphery of a tornado — where deck fastening, edge metal, and covering attachment decide whether a roof stays on. Those upgrades are cheap during a re-roof and impossible afterwards.
The short versionSection link
There is no nationwide building code for site-built houses in the United States, and no national tornado standard for them either. Design-load provisions, adopted editions, and local amendments differ by jurisdiction, so treat every figure here as a description of what a named document says — not as a requirement at your address. Confirm anything you intend to rely on with your authority having jurisdiction.
- The honest limit
- No roof covering is rated for a violent tornadoASCE 7-22 added tornado loads to design practice, but the Florida Building Commission's fact sheet on the change records that they apply only to Risk Category III and IV buildings — those posing a substantial hazard to human life if they fail, and essential facilities — and that the speeds used correspond to EF0 to EF2 intensity. A single-family house is neither, so no tornado load requirement reaches it.
- The storm you will actually get
- Straight-line thunderstorm wind, from about 50–60 mph upNOAA's National Severe Storms Laboratory classifies damaging winds as those exceeding 50–60 mph, and states that damage from severe thunderstorm winds accounts for half of all severe reports in the lower 48 states and is more common than damage from tornadoes.
- How tornado strength is decided
- Backwards, from the damage, after the stormThe Storm Prediction Center states plainly that the Enhanced Fujita scale "still is a set of wind estimates (not measurements) based on damage", judged against 28 damage indicators with 8 degrees of damage each.
- Derecho
- A wind damage swath of at least 250 milesSPC's criteria: a swath of wind damage at least 250 miles (about 400 kilometres) long, gusts of at least 58 mph along its length, several well-separated gusts of 75 mph or more, and a system moving faster than the mean wind. Most common May through August.
- What a shingle wind class tests
- A new shingle, in a lab, under a defined airflowIBHS records that ASTM D3161 Class A, D, and F correspond to 60, 90, and 110 mph of fan-driven flow, and that those speeds "relate to the wind speed flowing up the roof – not wind loads". Both D3161 and D7158 "evaluate new products and do not account for the effects of weathering, temperature, aging, or similar factors".
- Deck fastening — the cheap link
- Ring-shank nails, to a schedule FEMA now points at rather than printsThe second edition of FEMA P-804 (April 2023) no longer publishes its own nailing table. It requires the deck to be "inspected and renailed (if required) in accordance with Section 4.3 of the 2020 FORTIFIED Home Standard", caps that prescriptive route at a Basic Wind Speed of 130 mph and Exposure Category C, and adds one FEMA grant condition of its own: where sheathing is thicker than 15/32 in, the supplemental fasteners must be ASTM F1667 RSRS-03 ring-shank nails, 2½ in × 0.131 in.
- Sealed roof deck — the backup
- Up to 95% less water entry than a bare deckIBHS's own figure from its sealed-roof-deck testing. IBHS also states that the FORTIFIED Home programme "essentially assumes that a roof cover will be lost in a significant high-wind event" and that the sealed deck is the back-up plan for when that happens.
- Tornado vs straight-line, on the ground
- Inflow leaves debris at angles; outflow leaves it parallelThe National Weather Service office in Northern Indiana: all wind flows into a tornado, so debris lies at angles from the curving inflow; all wind flows out from a downburst, so debris lies in straight lines parallel to the outward flow. Twisted trees are not proof of a tornado.
This page's advice — buy attachment, not a rating — and the cases where that advice is wrongSection link
The position here is that money spent on how the roof is fastened outperforms money spent on a number printed on a shingle wrapper, and that the moment to spend it is while the deck is exposed. There are real situations where that is not the right call.
Best when
- A re-roof is already happening or is due within a couple of years, so the deck will be exposed and the nailing schedule, the edge metal, and the underlayment are all in scope at once.
- The house is in a derecho or severe-thunderstorm corridor, where the design case is a 60–90 mph gust event that arrives several times a decade rather than a once-in-a-lifetime tornado.
- The existing deck was fastened with staples or short smooth-shank nails — the condition a re-nailing schedule exists for, and the one an evaluator is looking for when the covering comes off.
- There are gable ends, deep rake overhangs, or a complicated roof with several edges and corners, because that is where suction is largest and where FEMA singles out both the gable end walls and their overhangs as particularly vulnerable.
- The soffits are coming off anyway. FEMA suggests retrofitting the roof-to-wall connections during soffit work or a roof-covering replacement, while those connections are more easily accessible; otherwise they are buried.
- An insurer or a state programme recognises a verified roof standard such as IBHS FORTIFIED, so the work is documented by someone other than the contractor who did it.
Think twice if
- The roof is sound and years from replacement. Tearing off a healthy roof to improve its nailing is rarely the best use of the same money — and the deck-fastening work FEMA describes is written for the moment the covering is off anyway.
- The real exposure is a violent tornado and the goal is occupant safety. Then the money belongs in an ICC 500 storm shelter or a FEMA safe room, not in the roof. FEMA says so directly.
- The openings are the weak point. The Building America Solution Center notes that failure of a window or door can allow high winds to enter and overpressurise the home, causing roofs and/or walls to fail — a perfectly nailed deck does not help if the front door lets the storm inside.
- Nobody has looked at the structure. FEMA puts developing a continuous load path in its most invasive tier and requires an engineered solution by a registered design professional wherever site conditions exceed its prescriptive limits. Re-nailing a deck onto framing that is not tied to the walls moves the failure down one link, it does not remove it.
- The house predates 1990 and the work would disturb old shingles, felts, or mastics, which may contain asbestos. The EPA says you generally cannot tell by looking, that a home should be inspected by a trained and accredited asbestos professional before remodelling that could disturb building materials, and that taking samples yourself is not recommended. Inspection comes before disturbance.
- A door-knocker is quoting it three days after a storm. The NWS's own after-the-storm guidance tells people to be aware of insurance scammers if their property has been damaged; urgency about a mitigation upgrade is a sales technique, not a weather fact.
What changes the answer
- The site: basic wind speed, exposure category, building height, roof geometry, enclosure classification, and risk category all feed the design pressures, and none of them is on a product label.
- Which pressure zone a given part of the roof is in. Field, perimeter, and corner see different suction, which is why fastening schedules change within a few feet of an edge.
- What is under the covering already — plank decking, thin sheathing, staples, or a deck that has been re-covered twice.
- Roof shape. FEMA identifies gable end walls as particularly vulnerable to out-of-plane wind loads, and treats a gable end overhang longer than nine inches as its own retrofit item.
- When in the year the roof goes on. IBHS records that manufacturers recommend 70–80°F for shingles to seal and warn that below 40°F they may not seal properly; an unsealed shingle is a loose shingle until spring.
- Whether the attic vents are wind-and-rain rated. A roof that stays on can still deliver water to the ceiling through a ridge vent in a horizontally driven rain.
- Your insurer, your state, and your policy. Credits, deductibles, and what counts as a covered loss are decided by that document and that jurisdiction, not by this page.
- Whether you are staying. Attachment upgrades pay off over decades of storms; they do not show up in a listing photograph.
Two mechanisms, one chainSection link
Wind damages a roof two ways that have almost nothing in common: it pulls, and it throws things. The first is a chain of connections and is genuinely improvable. The second is largely luck.
Wind does not push a roof off a house. It flows over it, separates at the edges, and produces suction — negative pressure — on the outside of the covering. The Building America Solution Center puts the consequence in one sentence: “Uplift forces acting on the roof are met with roof-wall connections that distribute the forces down the walls and into the foundation along the continuous load path.” Every one of those connections is a link, and a chain parts at the weakest one.
That is why the useful question about a roof in high wind is never “what is it made of.” It is “what is it attached with, and what is that attached to.”
1 · Covering to deck
An asphalt shingle is held down twice: by the nails driven through its nailing zone, and by the sealant strip — a heat-activated adhesive applied at the factory that bonds each course to the one below it once the roof warms up. IBHS describes the wind resistance of asphalt shingles as “directly related to the ability of the sealed shingle to resist the force of the wind acting to lift it from the shingle below,” and warns that “until shingles are fully sealed, wind and rain pose a risk to the roof.”
This is the link most often broken by the calendar rather than by the storm. IBHS records that in summer warmth a roof may seal in one to two weeks, but under less-than-optimal conditions it can take one to two months or more, that manufacturers recommend 70–80 °F, and that temperatures below 40 °F may not allow shingles to seal properly. A November roof in Kansas can go into March as a stack of loose tabs held only by nails.
2 and 3 · The deck, and the deck to the framing
The roof deck is the structural skin. If the covering blows off, the house gets wet. If the deck blows off, the house is open. The fastener that changes that link is the ring-shank nail, which resists being pulled back out in a way a smooth shank does not.
Be careful where you get the schedule from. FEMA’s wind retrofit guide, FEMA P-804, is written for one- and two-family houses in hurricane-prone regions — FEMA’s own overview says much of it may also be applied to non-coastal areas subject to high winds, which is the basis on which it appears here. It was reissued in April 2023 as a second edition that replaces the 2010 first edition, and one of the things it changed is that it no longer prints a nailing table of its own. It now requires the deck to be “inspected and renailed (if required) in accordance with Section 4.3 of the 2020 FORTIFIED Home Standard”; it limits that prescriptive route to a Basic Wind Speed of 130 mph and Exposure Category C, above which the deck “is required to be attached to resist the site-specific design loads specified in ASCE 7-22 determined through an engineering analysis” by a registered design professional; and where FEMA money is involved and the sheathing is thicker than 15/32 in, it requires the supplemental fasteners to be ASTM F1667 RSRS-03 ring-shank nails at 2½ in × 0.131 in.
Two consequences follow for a homeowner. The first is that older write-ups of this subject — including a great many contractor pages, and the 2010 edition of the FEMA guide itself — quote an 8d ring-shank at 0.113 in × 2⅜ in on a four-foot edge-zone schedule. That was FEMA’s published table until 2023, and it is not the current requirement. The second is that the edge zone itself is not a fixed four feet. It is a pressure zone, and how wide it is depends on the building, which is why the diagram above draws it without a dimension.
IBHS makes the same move in plainer language for its FORTIFIED programme: ring-shank nails, more of them, in a tighter pattern. Its programme site says using them “nearly doubles the strength of your roof against the forces of winds” — read that as the programme’s own summary rather than a test result, because no test, load, or comparison is named beside it. The direction is not controversial. The multiplier is marketing copy.
4, 5 and 6 · Framing, wall, foundation
Below the deck the chain becomes structural, and it stops being a roofing decision. FEMA puts the boundary plainly: wherever site conditions exceed the limits of the prescriptive solutions in its guide, “an engineered solution by an RDP” — a registered design professional — “in accordance with ASCE 7-22 is required.” Developing a continuous load path is not in the basic package at all; it sits in the guide’s most invasive tier, aimed at houses being substantially renovated or rebuilt.
This matters at wind speeds well below a design event. FEMA rebuilt the guide around Hurricane Ida, which it records was “not a design wind event for residential buildings” and which still produced, in the words of the reconnaissance team it quotes, “light-framed wood metal plate trusses… lifted off exterior walls” in a way that “enabled gable end walls to collapse.” The same team concluded that the most catastrophic damage to many single-family houses “was preventable or could be mitigated by cost-effective retrofits.”
The one place this becomes affordable is the soffit. FEMA suggests retrofitting the roof-to-wall connections “when retrofitting the soffits or replacing the roof covering… while the connections are more easily accessible.” If soffits are already coming down, ask.
7 · The edge, which is where it usually starts
Suction is not uniform across a roof. It concentrates at edges and corners, which is exactly where the covering is a free edge with nothing lapped over it. Two details do the work there. The drip edge — the L-shaped edge metal along eaves and rakes — and the starter course, the first strip of material laid before the visible shingles. IBHS describes the starter strip as installed at both the eaves and the rake edges, where it “helps prevent water intrusion and protects against uplift from wind that can occur at the roof edges.” FORTIFIED goes further and requires a wider drip edge and a fully adhered starter strip. FEMA P-804 says a drip edge “should be installed at gable rakes and eaves,” and is specific about the sequence: it “is required to be installed over the underlayment to help secure the underlayment in place at the edges of the roof.” Do not take that to the roof as a universal rule. The Department of Energy’s Building America Solution Center records the disagreement plainly: other bodies recommend the underlayment overlap the drip edge at the eave, to keep water from getting behind it. Which way round it goes at the eave is a real question with two published answers, and the one that governs is your adopted code and the covering manufacturer’s instructions.
Get the edge wrong and the failure is progressive: wind gets under the first course, peels it, and each lost course exposes the nails of the next one. That is why a roof after a windstorm is so often intact in the middle and stripped in a fan shape from one corner.
The other mechanism: debris
Uplift is a chain. Debris impact is not. A section of someone else’s roof deck, a length of fence rail, or a limb arriving at storm speed does not care how the covering is fastened — it punches through, and the mitigation for it is not a better nail.
It is worth knowing what the tested debris threat actually covers, because it calibrates everything. The windborne-debris standard used in residential construction, ASTM E1996 tested per ASTM E1886, is a test for openings — windows, doors, shutters. FEMA P-804 requires windows and skylights to be impact-resistant or protected to “the Large Missile D from ASTM E1886 and ASTM E1996 and AAMA 506,” and it is blunt about how far that gets you: a standard missile “will breach the code-prescribed wood structural panel shutter,” which is why plywood over the windows is not eligible for a FEMA grant at any wind speed.
That is the tested threat, and it is a threat to glass. A violent tornado throws cars. There is no equivalent tested debris class for a roof covering at all, and nobody sells one.
So the two mechanisms split cleanly. Uplift is improvable, cheaply, at a known moment. Debris impact is a matter of what is upwind of you, and the honest mitigations are keeping trees maintained, protecting openings so the house does not pressurise from the inside, and — for people rather than property — a shelter.
What each standard and programme actually testsSection link
Six things get quoted at homeowners as though they were the same kind of claim. They are not. This table is the difference between them, built from the documents themselves.
| Standard or programme | What is physically tested | What the label means | What it cannot tell you |
|---|---|---|---|
| ASTM D3161 (shingles) | A shingle sample on a test deck in a fan-driven airstream, for two hours. | Class A, D and F correspond to 60, 90 and 110 mph of that airflow. | IBHS notes the speeds relate to the wind flowing up the roof, not to wind loads — and the sample is new. |
| ASTM D7158 (shingles) | Two parts: a 35 mph smooth-flow test measuring the suction peeling the shingle, then a machine pull on ten sealed samples. | Class D, G and H. IBHS tabulates them at 90/120/150 mph under the 2005 version and 115/150/190 mph under the 2016 version. | The same class letter carries a different mph figure depending on the edition, so a bare number without its standard and edition is not comparable to anything. |
| IBHS FORTIFIED Roof | Nothing is tested on your house. A prescriptive package — ring-shank nailing, sealed deck, wider drip edge, adhered starter, rain-resistant vents, rated cover — is verified by an independent evaluator. | That this specification was followed on this building. | It is not a code approval and not a promise. IBHS states the programme essentially assumes the roof cover will be lost in a significant high-wind event. |
| ASCE 7-22 Chapter 32 (tornado loads) | Nothing physical. It is a design calculation an engineer performs on a building. | Per the Florida Building Commission, it applies only to Risk Category III and IV buildings, at speeds corresponding to EF0–EF2 intensity. | A single-family house is in neither of those categories, so no tornado load requirement reaches it. The same fact sheet says the provisions do not come close to storm-shelter life-safety targets. |
| ICC 500 shelter / FEMA safe room | A separately designed and constructed room, to a life-safety standard. | Occupant protection. FEMA describes safe rooms as offering near-absolute protection. | It protects people, not the roof. FEMA says a safe room's protection is much greater than any level of protection detailed in its wind retrofit guide. |
| ASTM E1996 / E1886 (windborne debris) | A missile fired at a window, door or shutter assembly, plus cyclic pressure loading. | FEMA P-804 requires openings to meet 'the Large Missile D from ASTM E1886 and ASTM E1996 and AAMA 506'. | It is a test for openings. There is no equivalent tested debris class for a roof covering — and FEMA notes a standard missile will breach a plywood shutter. |
Read this table one item at a time
ASTM D3161 (shingles)
- What is physically tested
- A shingle sample on a test deck in a fan-driven airstream, for two hours.
- What the label means
- Class A, D and F correspond to 60, 90 and 110 mph of that airflow.
- What it cannot tell you
- IBHS notes the speeds relate to the wind flowing up the roof, not to wind loads — and the sample is new.
ASTM D7158 (shingles)
- What is physically tested
- Two parts: a 35 mph smooth-flow test measuring the suction peeling the shingle, then a machine pull on ten sealed samples.
- What the label means
- Class D, G and H. IBHS tabulates them at 90/120/150 mph under the 2005 version and 115/150/190 mph under the 2016 version.
- What it cannot tell you
- The same class letter carries a different mph figure depending on the edition, so a bare number without its standard and edition is not comparable to anything.
IBHS FORTIFIED Roof
- What is physically tested
- Nothing is tested on your house. A prescriptive package — ring-shank nailing, sealed deck, wider drip edge, adhered starter, rain-resistant vents, rated cover — is verified by an independent evaluator.
- What the label means
- That this specification was followed on this building.
- What it cannot tell you
- It is not a code approval and not a promise. IBHS states the programme essentially assumes the roof cover will be lost in a significant high-wind event.
ASCE 7-22 Chapter 32 (tornado loads)
- What is physically tested
- Nothing physical. It is a design calculation an engineer performs on a building.
- What the label means
- Per the Florida Building Commission, it applies only to Risk Category III and IV buildings, at speeds corresponding to EF0–EF2 intensity.
- What it cannot tell you
- A single-family house is in neither of those categories, so no tornado load requirement reaches it. The same fact sheet says the provisions do not come close to storm-shelter life-safety targets.
ICC 500 shelter / FEMA safe room
- What is physically tested
- A separately designed and constructed room, to a life-safety standard.
- What the label means
- Occupant protection. FEMA describes safe rooms as offering near-absolute protection.
- What it cannot tell you
- It protects people, not the roof. FEMA says a safe room's protection is much greater than any level of protection detailed in its wind retrofit guide.
ASTM E1996 / E1886 (windborne debris)
- What is physically tested
- A missile fired at a window, door or shutter assembly, plus cyclic pressure loading.
- What the label means
- FEMA P-804 requires openings to meet 'the Large Missile D from ASTM E1886 and ASTM E1996 and AAMA 506'.
- What it cannot tell you
- It is a test for openings. There is no equivalent tested debris class for a roof covering — and FEMA notes a standard missile will breach a plywood shutter.
None of these six is convertible into any of the others, and none of them is a statement about the wind at your address. That is a site-specific engineering calculation, and it belongs to a design professional.
Uplift and debris impact, side by sideSection link
“Wind damage” covers two mechanisms that share almost nothing — not the physics, not the mitigation, and not the honest expectation of what money can buy.
| Uplift failure | Debris impact | |
|---|---|---|
| The mechanism | Airflow separating over the roof creates suction on the outside of the covering. The force is carried down a chain of connections to the ground. | A solid object arrives at storm speed and punctures, tears, or shears whatever it hits. |
| Where it starts | At edges, corners, rakes and gable ends, where suction is highest and the covering has a free edge. | Anywhere. It is a function of what is upwind, not of how the roof is detailed. |
| How it progresses | Progressively. Each lost course exposes the fasteners of the next, so damage spreads uphill from one point. | It does not progress. There is a hole, and then water comes through the hole. |
| What genuinely changes it | Deck fastening, edge metal, starter course, correct nail placement, sealed shingles, roof-to-wall connections, protecting openings so the house does not pressurise. | Tree maintenance, what your neighbours' roofs are fastened with, and distance from loose material. Very little of it is on your roof. |
| What does not change it | A higher wind class on the wrapper, if the nailing schedule, the edge, and the deck below are unchanged. | Any roofing product sold as impact resistant. Those classifications are hail tests; the tested debris standard applies to openings. |
| The honest expectation | Meaningfully improvable, for a small fraction of the re-roof cost, at a known moment. | Not meaningfully improvable at the roof. If the concern is people rather than property, the answer is a shelter. |
Read this table one item at a time
The mechanism
- Uplift failure
- Airflow separating over the roof creates suction on the outside of the covering. The force is carried down a chain of connections to the ground.
- Debris impact
- A solid object arrives at storm speed and punctures, tears, or shears whatever it hits.
Where it starts
- Uplift failure
- At edges, corners, rakes and gable ends, where suction is highest and the covering has a free edge.
- Debris impact
- Anywhere. It is a function of what is upwind, not of how the roof is detailed.
How it progresses
- Uplift failure
- Progressively. Each lost course exposes the fasteners of the next, so damage spreads uphill from one point.
- Debris impact
- It does not progress. There is a hole, and then water comes through the hole.
What genuinely changes it
- Uplift failure
- Deck fastening, edge metal, starter course, correct nail placement, sealed shingles, roof-to-wall connections, protecting openings so the house does not pressurise.
- Debris impact
- Tree maintenance, what your neighbours' roofs are fastened with, and distance from loose material. Very little of it is on your roof.
What does not change it
- Uplift failure
- A higher wind class on the wrapper, if the nailing schedule, the edge, and the deck below are unchanged.
- Debris impact
- Any roofing product sold as impact resistant. Those classifications are hail tests; the tested debris standard applies to openings.
The honest expectation
- Uplift failure
- Meaningfully improvable, for a small fraction of the re-roof cost, at a known moment.
- Debris impact
- Not meaningfully improvable at the roof. If the concern is people rather than property, the answer is a shelter.
A single storm normally delivers both, which is why post-storm assessments so often produce two different-looking damage patterns on one roof.
What is cheap while the deck is open, and impossible once it is closedSection link
FEMA states the case for the timing directly: strengthening the connections from the roof sheathing to the roof framing members is “a cost-effective and critical retrofit to implement when the roof covering is being replaced.” That sentence is the whole argument of this section. Everything below is either free to specify now, or a second tear-off later.
What FEMA pointedly does not publish is a single running order. Its retrofits “are not necessarily listed in the order in which they should be completed,” and the order “depends on the configuration of the house.” Two fixed points are worth holding a contractor to anyway: damaged framing gets repaired or replaced before anything is fastened to it, and before the deck is sealed it “should be dry and be broom-cleaned to ensure a smooth surface.” A sealed deck rolled over a wet or dirty deck is a sealed deck that will not stay sealed.
Available only while the covering is off
- Re-nailing the deck to the framing. Once the new covering is on, the fastener heads are buried under it and the only way back is another tear-off.
- Sealing the deck — taped joints or a full self-adhered membrane. This is not a product upgrade to the covering; it is a layer underneath it that only exists at this moment.
- Replacing or upgrading edge metal at both eaves and rakes, with the correct sequence relative to the underlayment.
- Seeing the deck. Delamination, previous water damage, undersized or gapped sheathing, and prior repairs are all visible for exactly one day.
- Photographing all of it. Documentation of what is under a roof is worth more than any adjective in a proposal, and it cannot be produced retrospectively.
Available while the soffits are off
- Roof-to-wall connections — the link FEMA suggests retrofitting during soffit work or a roof-covering replacement, while it is more easily accessible, and which is otherwise sealed inside the assembly.
- Gable-end overhangs. FEMA treats an overhang longer than nine inches as its own retrofit, to be rebuilt and connected as an outlooker.
- Confirming that intake ventilation at the eave is actually open, and that the soffit panels themselves are supported and fastened rather than friction-fitted.
Things that are not on this list, and why
Nothing here is a structural determination. FEMA puts a genuine continuous load path in its most invasive retrofit tier, and its prescriptive details stop at stated limits — deck attachment at a Basic Wind Speed of 130 mph and Exposure Category C, gable end overhangs at 180 mph and Exposure Category D — beyond which an engineered solution to ASCE 7-22 is required. A real building may not satisfy them. The purpose of this section is to make sure the questions get asked while asking them is still free — not to turn a re-roof into an engineering project by implication.
It is also worth naming what none of it buys. FEMA’s own summary of the limits applies to every item above: the occupant protection a safe room gives is “much greater than the protection provided by buildings that comply with the minimum requirements of most building codes or any level of protection detailed in this Guide.” A better-fastened roof is a property decision that pays off in the storms that happen most often. It is not a promise about the storm you are picturing.
What the classification tells you, and what it does notSection link
After a damaging wind event, two labels arrive: a National Weather Service determination of what the storm was, and a contractor’s account of what happened to your roof. They answer different questions and neither one settles the other.
The NWS determination comes from a damage survey. Its central clue is the direction of things: all wind flows into a tornado, so debris tends to lie at angles from the curving inflow; all wind flows out from a downburst, so debris tends to lie in straight lines parallel to the outward flow. The Northern Indiana forecast office also points out something that gets misread constantly — twisted trees are not proof of rotation, because structural asymmetries make a tree twist in straight-line wind the way a stop sign does.
That determination matters for the record, for warning verification, and sometimes for aid programmes. It does not tell you what wind hit your building. Enhanced Fujita ratings are, in the Storm Prediction Center’s own words, “a set of wind estimates (not measurements) based on damage” — and a rating describes the strongest damage anywhere along the path, not the wind at your address. A house near the edge of an EF3 path may have seen EF0 or EF1 winds.
The practical consequences are narrow and worth stating plainly:
- The storm’s classification does not change what your roof needs. A missing drip edge is a missing drip edge whether the wind rotated or not.
- It does not by itself determine coverage. Policy language, causation, and your deductible structure do that, and they vary by carrier and by state.
- It does change the story you will be told at the door. A tornado rating brings crews from out of state within days. The NWS’s own post-storm advice is to be aware of insurance scammers if your property has been damaged, and the contractor verification steps do not get suspended because the weather was dramatic.
- If water is coming in now, that is a different and more urgent page: what to do in the first hours of active intrusion, including where the stop-and-call-a-professional line sits.
What changes this on a real buildingSection link
- Wind
Wind performance is a property of a specific building on a specific site, not of a product. The design pressures on your roof depend on the basic wind speed mapped for the location, the exposure category around it, the mean roof height, the roof geometry, the enclosure classification, the risk category of the building, and which pressure zone — field, perimeter, or corner — a given square foot of it sits in. Change any one of those and the number changes.
This is why FEMA’s own prescriptive route stops where it does. Its deck-attachment solutions are “limited to a maximum Basic Wind Speed of 130 mph and Exposure Category C”; beyond that, the deck must be attached to resist site-specific design loads under ASCE 7-22, worked out by a registered design professional. A prescriptive schedule is not a determination for your house, and the same guide says so.
A marketing “130 mph roof” is not a code determination and never has been. Wind classifications are laboratory classifications of a product; design wind pressures are an engineering calculation for a building. Nobody can convert one into the other from a website.- Code and jurisdiction
There is no nationwide building code for site-built houses in the United States. States and local governments adopt and amend model codes, and the tornado provisions are a live example of how uneven that is: ASCE 7-22 introduced tornado loads, the Florida Building Commission’s June 2024 fact sheet on the change records that they apply only to Risk Category III and IV buildings, and whether that standard is referenced at all where you live depends on your jurisdiction’s adopted edition.
The same is true of everything else on this page. Whether a re-roof triggers deck-fastening upgrades, whether drip edge is required, what underlayment is required in a high-wind region, and whether a permit is needed at all are four separate local questions.
Record the jurisdiction, the adopted edition, the amendments, the effective date, and the official URL for any code claim, and confirm it with the authority having jurisdiction. Nothing here is a code determination for your building, and the Florida fact sheet cited above is Florida's law, not yours.- Structural weight
The links below the deck are structural engineering, not roofing. FEMA places developing a continuous load path in the most invasive of its three retrofit tiers, and requires an engineered solution by a registered design professional, to ASCE 7-22, wherever a building exceeds the limits of its prescriptive details. A roofer who offers to “strap the trusses” as a line item on a re-roof proposal is offering something outside the scope of a roofing contract, and the right response is to ask who designed it.
Do not treat any statement here as a structural determination. Uplift capacity, connection design, and load-path adequacy are answered by a licensed design professional looking at this building.- Moisture and ventilation
A roof can stay on and still let the storm in. Horizontally driven rain enters through ridge, off-ridge, gable and turbine vents, which is why FEMA P-804 treats attic ventilation openings as a retrofit item in their own right and why FORTIFIED requires attic vents that are wind and rain resistant. The water arrives on top of the ceiling insulation and shows up as a stain with no hole above it.
This is also where the sealed roof deck earns its keep. IBHS’s testing found that a sealed deck can reduce water entry by as much as 95% compared with a bare, unsealed deck — but note what that measures. It is a limit on the damage after the covering is gone, not a way of keeping the covering on.
Vented and correctly designed unvented assemblies are both legitimate, and this page does not tell you which one your house should have. Changing between them is a design decision with vapour-control, code, and warranty consequences.- Hail and impact
The storms that produce damaging straight-line wind frequently produce hail in the same hour, and an adjuster will look at both. They are separate mechanisms with separate tests and separate policy language — an impact classification is a hail test, not a debris test, and it says nothing about uplift. The hail page handles the impact ratings and their limits.
- Access and site conditions
Every assessment described here can be made without leaving the ground: lifted or missing tabs along a rake, a line of exposed nail heads, edge metal standing proud, granules in the gutters, a debris strike visible from an upstairs window, or a contractor’s photographs. If a roof needs to be walked, it is walked by someone insured to do it who has a reason to be there other than selling you something.
Do not go onto a storm-damaged roof and do not enter a damaged attic. The NWS's post-storm guidance is to stay out of damaged buildings and to contact local authorities about downed power lines.- Insurance and documentation
Coverage, deductibles, wind and hail deductible structures, depreciation, and what counts as a covered loss vary by carrier, by state, and by the facts of the claim. This page cannot tell you whether a specific loss is covered, whether a mitigation credit exists where you live, or what a verified roof designation is worth on a premium. What it can say is that documentation is free and retrospective documentation is not: have the deck photographed while it is open — by the crew that is already up there, not by you — keep the nailing schedule and the product data, and keep any third-party verification.
Nothing here is insurance advice or a statement about your policy. Coverage and claim outcomes are governed by your policy document and by the law of your state.
What a wind warranty actually promisesSection link
Wind is the clause where the gap between a marketing number and a contractual obligation is widest, and where the conditions attached to the promise do most of the work.
- The manufacturer's limited wind warranty
It is a warranty on the product, offered by the manufacturer, on the terms in that document. A wind-speed figure inside it is normally conditioned — on a specified fastener count and placement, on the manufacturer’s own starter and hip-and-ridge products being used, sometimes on enhanced application in high-wind regions, and on the shingles having sealed. Find the conditions before you find the number, because the conditions are what a claim turns on.
- The wind class on the wrapper
A classification under ASTM D3161 or ASTM D7158 is not a warranty at all. It is a laboratory result on new material. IBHS states that both standards “evaluate new products and do not account for the effects of weathering, temperature, aging, or similar factors.” Nothing about it is a promise to you.
- The installer's workmanship warranty
For wind, this is usually the document that matters, because most real wind failures trace to installation: nails outside the nailing zone, overdriven or underdriven fasteners, a missing or reversed starter course, drip edge sequenced wrongly relative to the underlayment. Read it for length, for whether a diagnostic visit is chargeable, for whether it transfers, and for what happens if the company stops trading. The warranty guide works through how these three documents interact.
- A verified roof designation
A programme such as IBHS FORTIFIED is neither a warranty nor a code approval. It is a prescriptive specification plus independent verification that it was followed on this building. Its value is that somebody other than the contractor confirmed the work — which is exactly what a photograph of an open deck cannot do on its own.
Repairability
Wind damage repairs badly. Individual blown-off shingles can be replaced, but the surrounding courses have to be broken free of their sealant to get at the nails, and the replacements have to seal into an aged roof — so a wind repair on a ten-year-old roof tends to create a small band of shingles that behave differently from everything around them. Colour matching is a secondary problem; the bond is the real one.
Creased shingles — bent at the nail line but still attached — are the awkward case. They are still on the roof, they are not a leak today, and their seal is broken. Whether they are treated as damage is a judgement call that different inspectors and adjusters make differently, and this page cannot make it for you. What it can say is that the question is about the seal, not about the appearance.
A warranty is a contract between a reader and whoever wrote it. What it covers, what voids it, whether it transfers, and how it is enforced are set by that document and by the law where the reader lives. Read the actual warranty for the product and the installer in front of you — not a summary of one, including this one.
Questions to ask an installerSection link
These are the questions that separate a proposal that improves wind performance from one that simply replaces a roof with the same roof.
While the deck is exposed, are you re-nailing it — and with what nail, at what spacing, and what does that add as a separate line?
The answer you want names a fastener, a written schedule it comes from, and two spacings — one for the field and a tighter one near the edges. FEMA’s current guide does not print that schedule itself; it sends you to Section 4.3 of the 2020 FORTIFIED Home Standard, and adds that where FEMA money is involved and the sheathing is thicker than 15/32 in the supplemental fasteners must be ASTM F1667 RSRS-03 ring-shank nails, 2½ in × 0.131 in. A contractor quoting a four-foot edge zone and an 8d ring-shank at 2⅜ in is quoting the 2010 edition. “We’ll nail off anything loose” is not an answer at all.
What is going on the deck before the covering — plain felt, synthetic, taped joints, or a full self-adhered membrane?
This is the sealed-deck question. FEMA P-804 requires the deck to be sealed in accordance with Section 4.4 of the 2020 FORTIFIED Home Standard rather than specifying a build-up itself; the Department of Energy’s Building America Solution Center summarises FORTIFIED’s three permitted methods as a full self-adhering polymer-modified bitumen membrane, taped sheathing joints with an underlayment over the whole deck, or two layers of underlayment in shingle fashion. Which one is being priced should be in writing.
What wind classification does the covering carry, under which standard, and under which edition of that standard?
IBHS tabulates ASTM D7158 Classes D, G and H at 90, 120 and 150 mph under the 2005 version of the standard and at 115, 150 and 190 mph under the 2016 version. The same class letter carries a different figure depending on which edition assigned it, so a bare mph number in a proposal is not a comparable quantity. Ask for the class and the standard.
Show me your eave and rake detail: drip edge gauge, where it sits relative to the underlayment, and what the starter course is.
The edge is where progressive failure starts. A specific answer names a metal thickness, a sequence, and a starter product rather than a cut-down shingle. FORTIFIED requires a wider drip edge and a fully adhered starter strip, which is a useful benchmark even if you are not pursuing the designation.
It is late in the season. Will these shingles seal before spring, and what will you do if they do not?
IBHS records that manufacturers recommend 70–80 °F and warn that below 40 °F shingles may not seal properly, and that sealing can take one to two months or more in poor conditions. Someone who has thought about this will have an answer about timing or hand-sealing. Someone who has not will tell you it doesn’t matter.
Are the attic vents you are installing rated for wind-driven rain?
A roof that survives the wind can still put water on the ceiling through a ridge vent. FEMA P-804 treats ventilation openings as a retrofit item; FORTIFIED requires wind- and rain-resistant vents. If the answer is the same vent that was there before, that is a choice being made silently.
Are the soffits coming off? If so, can the roof-to-wall connections be looked at while they are open?
FEMA suggests retrofitting roof-to-wall connections during soffit work or a roof-covering replacement, while those connections are more easily accessible. The honest answer from a roofing contractor may be “that is an engineer’s job” — which is correct, and is still worth knowing before the soffits go back up.
Require these in writing
- Deck fastener: type, shank, diameter, length, head style, and spacing — stated separately for the field and for the edge zone
- Whether the existing deck is being re-nailed, and the unit price if additional sheathing is required
- Underlayment or sealed-deck method, named by ASTM designation, and how it is fastened
- Drip edge material and thickness, at eaves and at rakes, and its sequence relative to the underlayment
- Starter course product at both eaves and rakes — not shingles cut down on site
- Covering wind classification, the standard, and the edition of the standard
- Fasteners per shingle and their placement relative to the nailing zone, including any enhanced high-wind pattern the manufacturer requires
- Attic ventilation products by model, with their wind-driven-rain performance
- Photographic documentation of the open deck and the completed nailing, delivered to you as files
Misconceptions and failure modesSection link
Common misconceptions
Common belief
These shingles are rated for 130 mph, so my roof is good to 130 mph.
What is actually true
Two different things are being conflated. A shingle classification is a laboratory result on new material under a defined airflow — IBHS notes that ASTM D3161’s speeds “relate to the wind speed flowing up the roof – not wind loads.” The wind your roof actually has to resist is a pressure calculated from the mapped basic wind speed, exposure, height, geometry, enclosure, risk category, and pressure zone for your building. A product class is an input to that calculation, not the result of it, and it says nothing about the deck, the framing, or the connections below the covering.
Common belief
A stronger roof would have saved that house in the tornado footage.
What is actually true
Not in the core of a violent one. NIST’s investigation of the 2011 Joplin EF-5 found that “virtually all of the buildings in which people died were affected by wind speeds equivalent to an EF-3 tornado or higher,” that the majority of deaths — 135, or 83.8 percent — were caused by impacts associated with building failure, and that regardless of construction type, buildings did not adequately protect occupants. Its key recommendation was for new performance-based standards for tornado-resistant design, which is a statement that they did not exist. What roof attachment changes is the much larger area around the core, and the far more common storms that never make the footage.
Common belief
Straight-line wind is the minor version of a tornado.
What is actually true
It is the common version, and it does more damage in aggregate. NOAA’s National Severe Storms Laboratory states that damage from severe thunderstorm winds “account for half of all severe reports in the lower 48 states and is more common than damage from tornadoes,” that speeds can reach 100 mph, and that a single event can produce a damage path extending for hundreds of miles. A derecho, under SPC’s criteria, is a damage swath at least 250 miles long with 58 mph gusts along its length. That is the storm the attachment details on this page are actually written for.
Common belief
Metal roofs don't blow off.
What is actually true
Metal is a covering material, not an attachment schedule. FEMA P-804 gives asphalt shingles and tile their own sections and puts everything else — metal included — under “All Other Roof Coverings,” where the test is documentary, not material: you obtain from the manufacturer “documentation showing that the roof covering and attachments were designed or tested for the applicable component and cladding wind pressures,” and all coverings “regardless of type” are installed to the manufacturer’s instructions for the design wind speed. Steel earns no exemption from that. An exposed-fastener panel with elongated screw holes and a free edge at the eave is not more wind-resistant than a well-nailed shingle roof because it is made of steel. Compare the two systems properly rather than by material folklore.
Common belief
The shingles are all still there, so the roof is fine.
What is actually true
A shingle can be creased at the nail line, or have its sealant bond broken, and stay in place until the next storm. Since the sealed bond is what IBHS identifies as the thing resisting uplift, a broken seal is a real change in the roof’s wind performance that is invisible from the street. The inspection question is about the bond, not about the count.
Common belief
Impact-resistant shingles will handle flying debris.
What is actually true
Impact classifications for roof coverings are hail tests. The windborne-debris standard used in residential construction, ASTM E1996 tested per ASTM E1886, applies to openings: FEMA P-804 requires windows and skylights to resist “the Large Missile D from ASTM E1886 and ASTM E1996 and AAMA 506” — a test for glass, not for a roof. No tested debris class exists for a roof covering.
How it actually fails
- Shingles that never sealed
- A roof installed in cold weather, in shade, or late in the season may not activate its sealant strip. IBHS records the manufacturers’ own numbers: 70–80 °F recommended, below 40 °F may not seal properly, one to two months or more to seal in poor conditions.What you can see: Tabs that lift and flutter in ordinary wind; a roof that loses shingles in its first spring at speeds it should have shrugged off; lifted courses visible along a rake from the ground.
- Progressive peel from an edge
- Wind gets under the first course at an eave or rake — usually because the starter course is missing, reversed, or a cut-down shingle without a sealant strip in the right place — and each lost course exposes the fasteners of the next one.What you can see: A fan- or wedge-shaped bare area spreading uphill from one corner, with the field of the roof untouched. Exposed nail heads along the leading edge of the loss.
- Deck panel loss in the edge zone
- Sheathing fastened with staples or short smooth-shank nails withdraws under repeated suction cycles. Re-nailing schedules exist precisely for that existing condition, and their tightest spacing is reserved for the edge zone, where suction is largest.What you can see: Not subtle from inside: daylight, and the storm in the attic. From outside, a rectangular hole the size of a sheet of plywood rather than a ragged patch.
- Internal pressurisation after an opening fails
- The Building America Solution Center: “Failure of a window or door can allow high winds to enter and overpressurise the home, causing roofs and/or walls to fail.” The roof is then being pushed from below and pulled from above at the same time.What you can see: A broken window or a failed garage door on the windward side, with roof damage that looks disproportionate to the wind speed recorded nearby.
- Wind-driven rain through vents
- Ridge, off-ridge, gable and turbine vents that are not rated for horizontally driven rain admit water while the roof is otherwise intact. FEMA P-804 treats them as a retrofit item; FORTIFIED requires wind- and rain-resistant vents.What you can see: Wet insulation in a band under the ridge with no damaged covering above it; ceiling staining that appears after a windy rain but never after a still one.
- Gable end and rake overhang failure
- FEMA states that gable end walls are particularly vulnerable to failure from out-of-plane wind loads, and treats the overhang as a separate problem: an overhang longer than nine inches “must be retrofitted to be constructed and connected as an outlooker.”What you can see: The rake overhang gone while the rest of the roof is intact, or the whole gable triangle displaced inward or outward.
Sources and further readingSection link
Understanding Roofing / Published
Scope and limitations
- It cannot tell you what wind your roof has to resist.
- That is a calculation from the mapped basic wind speed, exposure category, building height, geometry, enclosure, and risk category for your building, and it is made by a design professional, not by a website.
- It cannot tell you whether your roof would survive any particular storm.
- Nobody can.
- The Storm Prediction Center's own position is that Enhanced Fujita ratings are wind estimates inferred from damage, not measurements, so even after the fact the wind speed at your address is an inference.
- It does not publish a cost figure.
- No transparent national dataset separates the incremental cost of ring-shank re-nailing, a sealed deck, or upgraded edge metal from the cost of the re-roof they happen during, and a made-up number would be worse than none.
- It cannot tell you whether an upgrade is required, permitted, or credited where you live.
- Adopted code editions, local amendments, re-roof triggers, and mitigation credit programmes are jurisdiction-specific.
- It cannot tell you whether your insurance responds, what your wind or hail deductible is, or whether a verified roof designation changes your premium.
- Those are governed by your policy and by your state's law.
- It is written around asphalt shingle roofs on wood-framed houses, because that is the case the cited IBHS material covers in detail.
- FEMA's guide also addresses tile and treats everything else as 'All Other Roof Coverings'; those assemblies share the load-path logic but not the covering-specific detail discussed here.
- It does not reproduce a nailing schedule.
- FEMA's current guide does not print one either — it points at Section 4.3 of IBHS's 2020 FORTIFIED Home Standard, a private specification this page has not read, and caps its own prescriptive route at a Basic Wind Speed of 130 mph and Exposure Category C.
- The schedule for your roof comes from that standard, from your adopted code, or from a design professional, not from here.
Wind Retrofit Guide for Residential Buildings in Hurricane-Prone Regions (FEMA P-804, Second Edition)
Federal Emergency Management Agency / April 2023
That strengthening roof sheathing-to-framing connections is 'a cost-effective and critical retrofit to implement when the roof covering is being replaced'; that the roof deck is required to be inspected and renailed in accordance with Section 4.3 of the 2020 FORTIFIED Home Standard, that this prescriptive route is limited to a Basic Wind Speed of 130 mph and Exposure Category C, and that beyond it an engineered solution to ASCE 7-22 by a registered design professional is required; the FEMA grant condition that supplemental fasteners be ASTM F1667 RSRS-03 (2½ in × 0.131 in) nails where sheathing exceeds 15/32 in; that the deck is required to be sealed per Section 4.4 of the 2020 FORTIFIED Home Standard and should be dry and broom-cleaned first; that a drip edge should be installed at gable rakes and eaves and over the underlayment; that the existing covering should be removed entirely rather than recovered, and that a new covering should be rated for the design wind speed for the location or meet the applicable design wind pressures and be installed per the manufacturer's high-wind instructions; that coverings other than asphalt shingles and tile fall under 'All Other Roof Coverings', for which manufacturer documentation of design or testing for the applicable component and cladding wind pressures should be obtained and all coverings 'regardless of type' installed to the manufacturer's instructions for the design wind speed; that attic vents are required to comply with Section 3.3 of the 2020 FORTIFIED Home Standard; that gable end walls are particularly vulnerable to out-of-plane wind loads and that overhangs longer than nine inches must be reconstructed as outlookers, with that prescriptive route limited to 180 mph and Exposure Category D; that roof-to-wall connections should be retrofitted during soffit work or a roof-covering replacement while more easily accessible; that developing a continuous load path sits in the Advanced Mitigation Package; that openings must meet 'the Large Missile D from ASTM E1886 and ASTM E1996 and AAMA 506', that a standard missile will breach a code-prescribed wood structural panel shutter, and that plywood is not permitted as opening protection at any basic wind speed; that the retrofits are not listed in the order they should be completed; the Hurricane Ida findings, including that it was not a design wind event for residential buildings; and that a safe room's occupant protection is much greater than any level of protection detailed in the Guide, safe rooms offering near-absolute protection.
This second edition explicitly replaces the December 2010 first edition, which is the version most secondary write-ups still quote; figures from the 2010 edition — an 8d ring-shank at 0.113 in × 2⅜ in, 6-inch and 4-inch schedules, a four-foot roof edge zone, and named ASTM D1970 and D226 underlayment build-ups — are no longer what FEMA publishes. It is best-practice guidance and FEMA grant criteria, not adopted law anywhere. It is written for one- and two-family dwellings in hurricane-prone regions, though FEMA's own overview says much of the guidance may also be applied to non-coastal areas subject to high winds. It leans heavily on IBHS's 2020 FORTIFIED Home Standard, which is a private specification this page has not read directly, so no nailing spacing is reproduced here. Read from a third-party mirror of FEMA's own PDF because fema.gov refuses automated requests; the URL given is FEMA's.
FEMA Advisory: Overview of FEMA P-804 (2023), Wind Retrofit Guide for Residential Buildings in Hurricane-Prone Regions
Federal Emergency Management Agency / July 2023
That FEMA released a second edition of FEMA P-804 in 2023, last published in 2010; that its Mitigation Packages now correspond closely to IBHS's 2020 FORTIFIED Home Standard; that it references ASCE/SEI 7-22, the 2024 ICC model building codes and ICC 600-2020; and that although written for hurricane-prone regions, much of the guidance may also be applied to non-coastal areas subject to high winds.
A six-page summary advisory, not the guide itself. It describes the second edition rather than setting requirements, and it does not reproduce any fastening schedule.
Roof 101
Insurance Institute for Business & Home Safety (IBHS)
That the wind resistance of asphalt shingles is directly related to the ability of the sealed shingle to resist the force of the wind lifting it from the shingle below, and that until shingles are fully sealed wind and rain pose a risk; the sealing timeline of one to two weeks in summer warmth and one to two months or more in less-than-optimal conditions; the manufacturers' recommended 70–80 °F and the warning that below 40 °F shingles may not seal properly; the ASTM D3161 classes A, D and F at 60, 90 and 110 mph and that those speeds relate to the wind speed flowing up the roof rather than to wind loads; the ASTM D7158 two-part test and its class table of D, G and H at 90/120/150 mph under the 2005 version and 115/150/190 mph under the 2016 version; that both standards evaluate new products and do not account for weathering, temperature or aging; that FORTIFIED requires ring-shank nails, more of them and in a tighter pattern; and that the starter strip is installed at eaves and rake edges and protects against uplift at the roof edges.
IBHS is an insurance-industry research organisation, not a standards body or a code authority. Its FORTIFIED requirements are a private specification, not law, and its summaries of ASTM test methods are summaries — the standards themselves are the authority on what they test.
FORTIFIED Roof
FORTIFIED — a programme of IBHS
That FORTIFIED requires a sealed roof deck, ring-shank nails installed in an enhanced pattern, a wider drip edge and a fully adhered starter strip, attic vents that are wind and rain resistant, and a roof cover meeting testing and rating requirements; and the programme's statement that using ring-shank nails nearly doubles the strength of a roof against the forces of wind.
A programme specification, not a code requirement and not a warranty. It does not state a wind speed the designation protects against, and this page does not imply one.
A Brief History of IBHS Sealed Roof Deck Research
Insurance Institute for Business & Home Safety (IBHS)
That IBHS's study found a sealed roof deck can reduce water entry into a home by as much as 95% compared to a bare, unsealed roof deck; and that the FORTIFIED Home programme essentially assumes that a roof cover will be lost in a significant high-wind event, with the sealed roof deck as the back-up plan.
The 95% figure comes from IBHS's own laboratory test chamber under defined wind and rain conditions, not from field loss data, and it measures water entry after the cover is gone rather than any reduction in the chance of losing the cover.
Facts about Derechos
NOAA Storm Prediction Center
The derecho criteria — a swath of wind damage at least 250 miles (about 400 kilometres) long, gusts of at least 58 mph along its length, several well-separated gusts of 75 mph or greater, radar features including bow echoes and rear-inflow jets, and a system moving faster than the mean wind; that more than 75% occur between April and August and that derechos are most common May through August; the two principal tracks, one paralleling the Corn Belt from the upper Mississippi Valley into the Ohio Valley and one from the southern Plains northeast into the mid-Mississippi Valley; and that the term was chosen to distinguish straight-line thunderstorm winds from the rotary winds of a tornado.
A climatological and definitional reference. It says nothing about building performance and is not a design document.
The Enhanced Fujita Scale (EF Scale)
NOAA Storm Prediction Center
That the Enhanced F-scale 'still is a set of wind estimates (not measurements) based on damage', judged against 28 damage indicators with 8 degrees of damage each; and the existence and ordering of the EF0 to EF5 categories used on this page.
The scale rates a tornado after the fact from the damage it caused. It is not a design wind speed, and a rating for a tornado is not the wind speed experienced at any particular building within it.
Severe Weather 101 — Damaging Winds Basics
NOAA National Severe Storms Laboratory
That damaging winds are often called straight-line winds to distinguish them from tornado damage; that damaging winds are classified as those exceeding 50–60 mph; that damage from severe thunderstorm winds accounts for half of all severe reports in the lower 48 states and is more common than damage from tornadoes; and that speeds can reach up to 100 mph and produce a damage path extending for hundreds of miles.
A public education page. The 'half of all severe reports' figure counts storm reports, which are a record of what was observed and reported, not a measure of dollars of damage.
Severe Weather 101 — Tornado Basics
NOAA National Severe Storms Laboratory
That tornado strength is determined after the fact by examining the damage and estimating wind speeds from it, rather than by measurement.
A public education page, not a design or building document. It says nothing about building performance. NSSL also records that tornadoes have been reported in all fifty states and calls the idea of a fixed 'tornado alley' misleading, which is worth knowing but is not a claim this page relies on.
Straight-Line Winds vs. Tornado: What's the Difference?
NOAA National Weather Service, Northern Indiana
That all wind flows into a tornado while all wind flows out from a downburst; that tornado debris is often left lying at angles because of the curving inflow while downburst debris lies in straight lines parallel to the outward flow; that twisted trees are not by themselves evidence of a tornado; and that NWS survey teams look for evidence of a circulation in debris fields to decide which occurred.
A local forecast office's public education page. Damage-pattern interpretation is complicated by terrain and by structure, and a survey uses radar, imagery, and eyewitness accounts alongside the debris field.
Tornado Loads — Impacts from ASCE 7-22
Florida Building Commission / June 2024
That the new tornado load design requirements in ASCE 7-22 apply only to Risk Category III and IV buildings; that the tornado speeds used correspond to EF0 to EF2 intensity, 'which are by far the most common tornadoes'; and that buildings designed to Chapter 32 'do not come close to meeting the more stringent life safety targets adopted for storm shelters', for which an ICC 500 consistent storm shelter would be needed.
A Florida document about the 8th Edition (2023) Florida Building Code. Its numeric tornado speeds are Florida-specific and are not used on this page. It carries its own disclaimer that it is general factual information and not a substitute for professional advice. Whether ASCE 7-22 applies where you live depends on your jurisdiction's adopted code edition.
NIST Investigation of Joplin, Mo., Tornado Details Proposed Measures for Saving Lives and Property
National Institute of Standards and Technology / November 2013
That the 22 May 2011 Joplin tornado was rated EF5; that virtually all of the buildings in which people died were affected by wind speeds equivalent to an EF-3 tornado or higher; that the majority of deaths — 135, or 83.8 percent — were caused by impacts associated with building failure; that regardless of construction type, buildings did not adequately protect occupants; and that NIST's key recommendation was the development and adoption of nationally accepted performance-based standards for the tornado-resistant design of buildings and infrastructure.
A news summary of NIST NCSTAR 3, published in 2013. It concerns one violent tornado and one community, and its recommendations are recommendations — they are not code anywhere by virtue of being made.
Hurricanes and High Winds Overview
U.S. Department of Energy, Building America Solution Center (PNNL)
That uplift forces acting on the roof are met with roof-wall connections that distribute the forces down the walls and into the foundation along the continuous load path; that failure of a window or door can allow high winds to enter and overpressurise the home, causing roofs and/or walls to fail; and its summary of the three roof-deck sealing methods permitted by IBHS FORTIFIED Roof — a full self-adhering polymer-modified bitumen membrane, taped sheathing joints with an underlayment over the entire deck, or two layers of underlayment in shingle fashion.
Best-practice guidance for builders and designers, not adopted law, and written primarily for the hurricane-prone region. Its own fastening figures are drawn from FEMA and IBHS documents cited above, and its account of the FORTIFIED sealing methods is a summary — the 2020 FORTIFIED Home Standard itself is the authority on what it requires. The continuous load path sentence quoted on this page appears there as a figure caption credited to FLASH.
Protect Your Family from Exposures to Asbestos
U.S. Environmental Protection Agency
That you generally cannot tell whether a material contains asbestos simply by looking at it unless it is labeled; that you may want your home inspected by a trained and accredited asbestos professional if you are planning to remodel, because remodeling can disturb building materials; and that a trained and accredited professional should take samples, with taking samples yourself not recommended.
General public guidance on asbestos in the home. It is not roofing-specific, and it does not establish which products in a particular roof contain asbestos. Abatement rules are federal, state, and local, and vary.
During a Tornado
NOAA National Weather Service
That in a tornado warning the NWS says to go to a basement, safe room, or an interior room away from windows; that a mobile home or a tent is not safe shelter; and its guidance about vehicles.
General public safety guidance. It is not building guidance and does not address roofs.
After a Thunderstorm
NOAA National Weather Service
That the NWS advises staying out of damaged buildings, contacting local authorities if you see power lines down, wearing long trousers, long sleeves and sturdy shoes when assessing damage, and being aware of insurance scammers if your property has been damaged.
General public safety guidance, not a structural assessment protocol.