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What the Derecho Taught Us About Iowa Roofs
Ironbridge Roofing Co. ·
At a Glance
- A derecho is a long lived straight line windstorm, not a tornado
- It hit a wide corridor across Iowa on 10 August 2020
- Wind failures start at edges, ridges and broken seal strips
- Nail pattern and wind rating are chosen once, at install
What a Derecho Is
A derecho is a fast moving line of thunderstorms that produces damaging straight line winds over a very long distance. Not a rotating storm. A wall of wind pushing in one direction for hours across hundreds of miles.
On 10 August 2020 one crossed Iowa and did catastrophic damage, particularly through the center of the state. Eastern Iowa felt it too, and it reset a lot of assumptions about what our weather is capable of.
What Straight Line Wind Does to a Roof
It does not lift a roof off in one piece, which is what people picture. It works on edges.
- Wind gets under a rake edge or an eave where the drip edge is loose
- It lifts the first course and breaks the seal strips along it
- The shingle drops back down, looking normal, no longer attached
- The next course is now exposed and the process walks up the slope
- Ridge caps, which sit highest and are fastened least, go first and fly furthest
That is why wind damage is so often invisible from the ground. The shingles are all still there. They are simply no longer stuck down. See Lesson 10.
The Three Decisions That Actually Matter
All three are made on install day and none of them can be added afterward.
- The wind rating of the shingle itself, which is stated by the manufacturer
- The nail pattern. Six nails per shingle instead of the minimum four, which is a small labor cost
- The edge detail. Proper drip edge at eaves and rakes, and a starter course with its own adhesive strip, which is where wind gets its grip
None of these is expensive at the time. All of them are impossible later. This is the part of a roofing estimate worth reading closely, and it is covered in Lesson 14.
After the Next One
There will be another. When it comes, the order is the same. Get everybody safe, stop the water, photograph everything before anything is covered, then deal with the claim.
And be careful about who knocks on the door in the week afterward. Lesson 18 is eight free checks that take fifteen minutes and rule out most of the ways this goes badly.
Want Somebody to Look at Yours
No sales call. A roofer looks at the roof and tells you what it needs.