- #Home designer architectural 2017 drawing insulation install#
- #Home designer architectural 2017 drawing insulation upgrade#
- #Home designer architectural 2017 drawing insulation windows#
While it’s true that actual whole-wall R-values will usually be higher than the values shown in the table (due to the R-values of the sheathing, drywall, and air-barrier membranes), both types of wall (open-cell and closed-cell) benefit equally from these additional R-values.
#Home designer architectural 2017 drawing insulation upgrade#
It demonstrates the calculation method and does a good job of estimating the incremental R-value attributable to an upgrade from open-cell to closed-cell foam. Moreover, the table doesn’t reflect the entire range of framing factors of different buildings. I haven’t included the R-value of the exterior OSB sheathing, the interior drywall, or the associated air films. I’m aware that the whole-wall R-value calculations in the table are simplified versions of actual whole-wall R-value calculations. It’s also worth considering an even more important issue: Most brands of closed-cell spray foam are more injurious to the atmosphere than open-cell spray foams, since most closed-cell spray foam is manufactured with a blowing agent that has a high global-warming potential. There are more cost-effective energy upgrades, such as exterior rigid foam or mineral-wool insulation, as I point out below. Closed-cell spray foam is expensive, and the incremental cost is mostly money down the drain.
#Home designer architectural 2017 drawing insulation install#
As a result, the heat loss due to thermal bridging through the framing is greater in a wall with closed-cell foam than it would be in a wall with open-cell foam.Ĭonsequently, if you install a closed-cell foam insulation with a high R-value per inch between your studs, you don’t really get the full value of your investment. (because the exposed portions of the studs are basically “indoors” and not part of the insulated wall assembly). of closed-cell foam insulation, the R-value of the studs is based on a stud depth of 3 in., not 3-1⁄2 in. When stud bays are partially filled with closed-cell spray foam, the exposed portion of the studs reduces their R-value in comparison to a wall that is totally filled with open-cell spray foam.
#Home designer architectural 2017 drawing insulation windows#
(U-factor is the reciprocal of R-value: U=1/R.) Let’s call the U-factor of the insulation “UI,” and the U-factor of the framing “UF.” Here’s how we calculate whole-wall U-factor for a wall without any windows or doors: To calculate whole-wall R-value, you first need to calculate the whole-wall U-factor. The remaining 75% of the wall consists of either stud bays filled with insulation or openings for windows or doors.
That means that about 25% of the wall area consists of studs, plates, and headers. A typical wood-framed wall has a “framing factor” of 25%. For example, a 2×4 wall without any windows can be divided into two areas: insulated stud bays and wood framing.
To calculate the whole-wall R-value of a wall, we have to divide it into areas, each with distinct R-values. Once cured, the soft foam is easily trimmed flush with the studs. Installers of open-cell spray foam will fill a 3-1⁄2-in.-deep cavity completely, allowing the foam to expand until it is proud of the studs. Open-cell spray foam isn’t as dense, so it’s easy to trim. This leaves the typically bumpy surface of cured foam and about a 1⁄2-in. To avoid having to trim closed-cell foam in a 2×4 wall, the installer will usually stop at a maximum depth of about 3 in., instead of the full 3-1⁄2 in. Closed-cell foam is so dense that it is difficult to trim. To understand why, we need to start by understanding the “trimmability” of cured foam. There isn’t much difference in the whole-wall R-value between a wall insulated with open-cell spray foam and one insulated with closed-cell spray foam.
What really matters is the R-value of the whole wall, not just that of the insulation. Both walls are affected by thermal bridging - the loss of heat through the wood framing - but there’s more to it than that. If you want to install spray foam in a stud wall, and price is no object, then it would seem to make sense to specify closed-cell spray foam, right? Well, not necessarily.
Open-cell spray foam has an R-value of about R-3.7 per inch, while closed-cell spray foam has an R-value that may be as high as R-6.5 per inch.
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