Installing dry sheets may seem like a dry topic but it is essential to any roof system. This fist layer determines how the new roof, either a composition roof or a flat roof, will perform against wind and breakage, and how it looks.
If the felt of a composition roof or the base sheet of a flat roof system like a built up (BUR) hot or cold, or even an SBS self adhered system is not flat, the material over it will not be just unsightly, it will be susceptible to breakage over time, breakage under foot, and can act as a place for wind to grab. Yes, wrinkled roofs blow off more than flat ones.
To keep the dry sheet flat the roofer needs to think like a carpet layer but on an incline. The roll of material is rolled out and nailed next to the roll on the high side. This is because gravity is pulling on the felts and if you nail it on the low side it will be loose. The roofer on the other end, where they started the roll, kicks the felt tight in the direction of the roll. Then it is nailed according to specified nailing patterns. If the felt or base sheet is left overnight it probably will be wrinkled. The roofer can wait until the sun flattens it out but if he left a flat roof open over night he would not be on my roofs anymore.
Thirty pound felt is more likely to wrinkle, sometimes even after the roof is installed. If you are going to pay the extra for thirty pound then you might as well buy a hybrid flat laying felt. These are strong like 30 lb. but lay flat like 15lb. Shinglemate by GAF, Gorilla by Atlas (boo hiss) and Roofer's Select by Certainteed are prime examples.
Self adhered base sheets are very flat laying but if there is a controlled environment underneath then moisture migration will be impaired. We roofers know not to mess with Mother Nature. Just use a nail-able base and an inter or mid ply sheet and you'll have a great system.
Anyway, if your roofer can't take the time to lay a flat felt then he just doesn't care.
go outside around dusk and look at your roof. If you see snake like bulges in your composition roof then the felt is wrinkled and the roof might blow off because it has something to grab.
Here in Dallas the weather can change on a dime. I've seen a warm day turn into a cold dark windy day in thirty minutes. Felts not installed according to the nailing pattern will wrinkle under these situations and can effect adversely the entire system.
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