Is your roof to flat for shingles
Too Flat For Shingles? Blog # 14
Tuesday, September 18, 2012
Too Flat For Shingles?
Q: I currently have a low sloped roof that has a rolled roofing surface. Can I re-roof it with composition shingles?
A: You have touched on a question which is near and dear to many homeowners.
Thousands of homes were built over the years with low sloped roofs. They were covered either by rolled roofing, or gravel surfaces.
Because lots of homeowners did not like the appearance of these products, manufacturers of composition shingles wrote specifications to allow their use, within certain, strict, guidelines, the first of which is the degree of slope.
The normal minimum slope for a shingle application is described as being 4 in 12. This means that for every 12 inches of run, a 4" rise is required, to assure proper drainage. (The steeper the pitch, the faster the runoff will occur).
This is important to understand, because on a lower slope, water will run off more slowly, giving it a greater chance to blow backward or sideways, finally finding an entry point (leak).
The manufacturers, to combat this problem, came up with a brilliant solution. Instead of a single layer of felt underlayment, which would be found on a normal slope, they require a second layer of underlayment, which is staggered, thereby preventing the intrusion of water, even when it is slowed down by lack of slope. Remember 1 layer of 30# astm felt is not the same as 2 layers of 15# felt. The important thing is the number of layers not the weight of felt.
The limit however, is an absolute minimum of 2 in 12, or 2" of rise for every 12" of run.
For slopes below the minimum, shingles may not be used, under any circumstances.
In addition to the slope requirement, the shingles must also be installed to a "double coverage" application.
Although it can seem confusing, the manufacturers specs have been the product of experience and evolution. It is crucial to follow them to protect both your home, and your warranty.
Hiring Raneri and Long, of course will assure that all is done properly, and that you can rest comfortably during any inclement weather.