Sooner or later, every remodeler will be
asked to reroof over an existing asphalt
shingle roof. But before adding a third,
or even a second, layer of 300-poundper-
square shingles, you have to make
sure the roof structure can handle the
load. The chart presented here (facing
page) is designed to help you do just
that. The top section of the chart
applies to situations where you are
adding a second layer of shingles; the
bottom section is for three layers (in
those cases where code allows — and
the customer insists).
You may be surprised when you use
the chart, because many older buildings
were never built to comply with building
code guidelines in the first