Low-slope roof replacement questions
Thanks for this great resource! I am planning to replace a 30 year-old 3-tab shingled roof on a circa 1959 house with a low slope (~2/12) in zone 2A (Houston, TX). I have been reading through a number of the articles relating to cathedral ceilings and low-sloped roofs, but I still have some questions. More details on the roof:
- The roof has soffit venting but no ridge vents;
- The roof system consists of two gable-ended roofs (main house plus garage/utilty room) that meet in a dead valley over about a third of the length of the smaller roof;
- It does have a spinner vent in the attic space, but the attic only covers a small percentage of the house (only enough to contain the HVAC system and about half of the ducting, which was replaced in 2014 with R-8 flex duct);
- The rest of the ducting is an original box duct that is behind sheetrock (and which has retrofitted duct wrap insulation);
- The rest of the roof has original batting between the rafters and gypsum board ceiling attached to the rafters;
- The attic space has been retrofitted with fiberglass batting at some point in the past;
- The existing roof decking is ship-lapped boards;
- Given the dead valley, there is about 12 feet on one side of each roof that is non-ventilated currently.
I’m certainly not planning to replicate the existing 3-tab roof (amazing that it lasted this long given the slope). I’d like to improve the roof’s thermal characteristics, though I’m mainly concerned with cooling performance given my location.
Should I be converting this to a non-ventilated roof?
Should I be looking at rigid foam above the shiplap with air channels above that, before another layer of sheathing and whatever roof I end up installing (standing seam, SBS, etc.?)
What options do I have for improving the under-sheath insulation?
Again, thanks for such a great resource.
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