Design for 2 layers of asphalt shingles?
Design for 2 layers of asphalt shingles?
(OP)
Is there a code requirement that requires an asphalt shingle roof to be designed for 2 layers (original plus one overlay). I work in California which still uses the 1997 UBC.
Thanks
Thanks






RE: Design for 2 layers of asphalt shingles?
RE: Design for 2 layers of asphalt shingles?
DaveAtkins
RE: Design for 2 layers of asphalt shingles?
RE: Design for 2 layers of asphalt shingles?
You buy shingles by their weight - say 220 or 240 which means 220 or 240 lbs per square and a square is 100 sq ft. Theoretically - the heavier the longer they live......
Therefore - a typical roof has about 2.5 lbs psf for one layer of shingles and add some for felt - like .5 psf
In roof truss design - 10 psf for dead loads if very typical and allows for two layers of shingles.
RE: Design for 2 layers of asphalt shingles?
RE: Design for 2 layers of asphalt shingles?
I remember reading in one of the codes (can't remember which one) that they limit the number of "reroofs" to one. Therefore you have the original roof and a reroof. If the roof requires another reroof down the road, the two existing roofs must be removed prior to the reroof (at least according to code).
RE: Design for 2 layers of asphalt shingles?
I tend to agree in that I was talkling about what most truss guys use - 10 psf dead TOP chord (shingles, plywood, etc.) and 10 psf dead on BOTTOM chord (drywall, insulation, lights, etc.)UNLESS otherwise specified.
If I was doing simple rafters - I would use something in the 20 psf range.
RE: Design for 2 layers of asphalt shingles?
Don Phillips
http://worthingtonengineering.com
RE: Design for 2 layers of asphalt shingles?
DaveAtkins