Roofing/flat roof


I am having my roof redone. It involves complete tear off Inspect for dry rot and here is the question part, the contractor suggests, installing 2 inch iso board insulation to roof deck   clean out all drains and reseal then install #75 lbs.fiberglass "A" base sheet mechanically to roof deck then flood coat entire surface with heavy layer of hot asphalt at aprox. 25 lbs. per square at 450 degrees,install 2 layers of ply IV fiberglass class "A" ply sheet with continuous mopping of asphalt between plies. Then finish with a "brilliant white Enery Cap class"A" cap sheet imbedded into hot asphalt. I live in Orange County a 1924 house and don't plan on selling soon. and the energy bill in the summer is huge, you can also feel the heat radiating from the ceiling during very hot summer days. Is this the way to go ? thank you in advance

The two inches of polyiso will have an R-value of approximately 11.7 to the new LTTR values for 2014. This will stop about 84% of your heat gain. The white cap sheet will also contribute to reflection of the heat.

Check with your local codes to see what thermal values apply for your area. They may adhere to ASHRAE 90.1 or the ICC (International Code). Once you know the acceptable R-value change the quote to suit. Find out the SRI value for the cap sheet and find out if it is Energy Star Rated.

This system will have to be better that the existing roof system. A little homework on your part will assist you in making a valid decision. you can also contact local roofing material suppliers as they should be cognizant of the info I have asked you to source.
All the best.

I do not live in the U.S. so I am not cognizant of your local codes.


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D. John Henderson


My 33 years in the building science business has involved air barriers, waterproofing, and flat & steep slope roofing systems.


My roofing encompasses commercial systems (BUR, mod-bit, single-ply) and residential applications (asphalt shingles, cedar shingles, slate and metal. I am cognizant of code stipulations in regards to FM and UL for commercial roofs.

Attended numerous courses offerd by Roof Consultants Institute, Roofing Industry Educational Institute, Factory Mutual Research Corporation, University of Wisconsin, and BURSI. Lectured for RCI and mentored at a local university for a Building Science Certificate.

Past/Present Clients
Government, commercial businesses such as The GAP, hospitals, school boards as a roof designer.

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