What happens if you use two layers of Tyvek on new construction instead of the customary one layer?
I use 2 layers of TG2 underlayment for most of my roofs, sometimes Polyglass depending on application. Most of my roofs requiring underlayment are concrete tile. We also have low slope roofs under 4/12 pitch that, without a question, we install a minimum of 2 layers of underlayment. In order of quality from low to high 1 layer of tarpaper 2 layers of tarpaper 1 layer of TG2 2 layers of TG2 Polyglass I don’t care if people say if you have one layer installed right you are paying extra for materials that are worthless. They obviously have not lived in Arizona where temperatures can reach 120 degrees. With that kind of extreme heat, tarpaper has a tendency to fail prematurely. The second layer adds another layer of protection. Our 25 year 3-tab shingles last about 7 years and our 30 year 3-tab shingles last about 10 years because of the extreme heat. Guarantee periods from roofers increase with the ‘better’ layers of protection for nominal fees.
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