Roofing/new roof



I have to replace a shingles roof plus part of the rood is flat,  here in Northern  AZ. where it is hot in summer and very cold in winter.  I got some quotes, some have more details than others..
What kind of vents should I insist upon?  Currently not much as it is an old house...  
Any other must requirement I should ask for?  For me it is much money to invest...

Thank you very much.  Gabe

Shingle roof: due to the warm summer climate I would suggest choosing a light colored shingle or even an EnergyStar rated shingle, white in color from Certainteed, GAF-Elk and Owens-Corning. Verify if there is an erebate program for your state for use of these products on your roof.

If it is an old house and there are no soffits where vents can be installed, the only other approach maybe to place roof vents in the lower part of the roof for air intake and vents in the high point or a ridge vent for air to escape.

If you have gable vents then do not install a ridge or roofvents.
Venting requirements usually follow this rule of thumb:
one square foot of venting for every 300 square feet of floor space below roof. This one square foot is then split between the soffit and the roof. If the ceiling is a cathedral ceiling the value changes to 1:150.

ex: 1200 sqaure foot of floor space at 1:300 ratio is 4 square feet of venting, equals to two square feet in the soffit and the same in the roof. An average roof vent is 50 square inches so two sqaure feet would be 5.76 roof vents (144 sqaure inches x 2) or 6 roof vents. check your local building code requirements.

Roof vents would be more durable if made out of metal but they are more costly them plastic.

Your flat roof could be covered by an Energystar rated modified membrane from Siplast, or Firestone. A cheaper approach if no foot traffic occurs would be GAF's |Extreme TPO membrane.

All the best.


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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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