Wind rating is not a wind speed you have survived
A 140 mph rating means the structure, anchored per spec, is engineered to resist the uplift and lateral load produced by a 3-second gust at 140 mph at standard exposure. It is a calculation, not a field test.
The critical phrase is anchored per spec. A 140 mph building on four undersized ground anchors is not a 140 mph building. Anchoring is where wind ratings are won and lost, which is why we include it in every build rather than selling it as an upgrade.
Exposure category matters more than people think
- Exposure B: suburban, wooded, sheltered. Lowest effective load.
- Exposure C: open terrain, scattered obstructions. Most rural sites.
- Exposure D: flat unobstructed terrain or within one mile of open water. Highest load.
- A building on an open mesa in Exposure D sees substantially more force than the same building behind a treeline in Exposure B at the same wind speed.
Snow load in pounds per square foot
| Ground snow load | Where it applies | Recommended spec |
|---|---|---|
| 5 to 10 psf | Gulf Coast, south Georgia, Louisiana | 14GA framing, any roof style |
| 10 to 20 psf | Oklahoma, Arkansas, Tennessee valleys | 14GA framing, vertical roof |
| 20 to 30 psf | Kentucky, east Tennessee ridges, NC mountains | 12GA framing, vertical roof |
| 30 to 40 psf | Western Virginia, high elevation NC | 12GA framing, vertical roof, reduced bay spacing |
Why ice is worse than snow
Fresh snow weighs roughly 7 pounds per cubic foot. Ice weighs about 57. An inch of ice accumulation loads a roof harder than most of the snow that falls all winter.
In Kentucky and Tennessee the design case is almost always an ice storm, not a snowfall. That is why we push 12GA framing there even when the published snow load looks modest.
How roof style changes the load
A vertical roof sheds snow and water down the panel ribs to the eave. A regular or horizontal roof runs water the length of the building along the panel seams, which means snow sits longer and water finds fasteners.
This is the entire argument for vertical roofs in any region with meaningful precipitation. It is not cosmetic.