Flat roof — sloping and insulation
I own a custom 2-3 story hillside 3300 square foot island home in Gig Harbor, WA (Climate Zone 4C) that was built in 1972. I am the second owner and purchased the home in 1986. The house roofing consists of 80% metal on a 6:12 pitch and a 20% flat roof (~560 square feet) over the bedroom wing with eight ceiling can lights adjoining clerestory windows. The house plans specify R-19 fiberglass batt insulation. The flat roof was replaced in 2001 with a ridge vent and torch down installed. This flat roof suffered a leak about three weeks ago and a few soft spots are apparent when walking on it. I am pressed to get this repaired before the fall and winter rains arrive. My inspection in 2001 revealed 2×10 joists on 16 inch centers. My goal is three-fold: put a slope on the roof, increase the insulation R-value to current code, and replace the roof membrane. I am 73 years old and in excellent health and planning to remain in the home.
I have been frustrated by the absence of a clearly defined solution. I have been in consultation with three roofers and two insulation companies and only now beginning to arrive at reasonable options.
To meet these goals two roofers have recommended the installation of an ISO board tapered system that would provide the slope and increase the R-value to an average of about 43 (31-65) and either a TPO (20 year warranty) or PVC (lifetime warranty) membrane covering. The irregular perimeter of this flat roof and one window would necessitate the tapered system to have a couple of peaks and valleys to direct water toward the roof scuppers. Each company has gone to roofing supply companies for computer generated plans for the tapering design which are not yet finalized.
The insulation companies are recommending somewhat differing solutions. One being a fully open-foam fill of the 2×10 joists across the flat roof. The other recommends a mix of Ram Board & 6” Closed Cell Spray Foam plus R-15 Fiberglass Insulation. Both of these applications would be made from the roof side before the final membrane was installed by the roofer. Of course, this would necessitate all the plywood sheeting being removed and the original fiberglass removed. Also, this does not answer the slope goal which would still have to be answered.
All agree to remove the ridge vent.
My questions are:
1) Regarding the tapered ISO board solution, should the original R-19 fiberglass batt insulation be removed to create a clean “warm” roof or can it remain in place which would save some costs?
2) Which membrane is recommended for this application; TPO or PVC?
3) After reading a number of posts on the subject I am tending towards a dark colored roof to minimize the interior moisture draw? Do you agree?
Thank you for your timely response.
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