11/16/2023 0 Comments Flat roof house problems![]() With this combo, you can achieve a total r value of about 47. of the roof cavity with dense packed cellulose. of closed cell foam insulation and fill out the remaining 10 in. Some pros may suggest it to a homeowner looking for alternative insulation materials that are inexpensive.įirst, install sloped decking as described in the first option. Mistake # 3: Yet another wrong way to raise the R value at a low cost If you can actually get into the crawl space, its much more effective to install blown in cellulose or fiberglass insulation. Once again, increasing the thickness of ISO will give you a higher r value at a much lower total cost. If on top of this you have to hire a spray foam specialist to install only 2 inches of foam, your costs will skyrocket. Our Take: The extra labor required to get inside a typically inaccessible crawl spaces under a flat roof will more than negate potential savings of using 30-R fiberglass batts. This option can give you a total r value of about 62. Then, R-30 batts can be added for additional efficiency at a lower price. of closed cell foam under it, as an air barrier. If someone wants to get a very high r value without breaking the bank, some contractors may propose this: Mistake # 2: Combining different types of insulation to increase R value We recommend having at least 20 r value worth of material for optimal energy efficiency. for a 1 inch board (equivalent of 6 r value). It is top quality and the most cost effective product for your flat roof. While expensive, the best insulation is PolyISO rigid foam. If moisture is a major concern, you can also install XPS rigid insulation, which offers superior moisture resistance. However, PolyISO absorbs considerably less water, therefore if it gets wet, it looses only a small fraction of its insulating properties. These problems typically come out when its too late to fix the roof, and complete replacement is in order. The worst part about this: you will not even know its happening. ![]() ![]() Moreover, you are also risking that underneath this wet insulation, you roof sheathing and deck will start to rot. Also, if a roof leaks and fiberglass insulation gets wet, it will loose most of its insulating properties. Our Take: Framing this out and buying 30-R fiberglass insulation will cost you about 50% more than just buying 5 inches of PolyISO (equivalent of 30-R).īecause it will take a lot of time to actually install all of this, you are risking major leaks, if it starts to rain before everything is complete. Then, install R-30 fiberglass batts between the rafters. It should be installed on tapered 2x furring strips, in order to slope the surface of the roof toward drains. When a homeowner really needs to cut down on costs, some contractors may suggest the following:Īdd an additional layer of OSB over the sheathing. Mistake # 1: Save money by installing Fiberglass Insulation, and framing out roof slope using OSB board substrate Some so called “experts” online may recommend the following, claiming to achieve a greater r value at a lower cost. Standing Seam Materials & Cost Calculator.
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