Insulation retrofit: what options should be considered?
I have a 2-story home built in the early 90s in Georgia, climate zone 3. It is oriented so the front of the house faces East. For a few reasons, I will be completely removing the front of the house down to the 2×4 studs, replacing existing single-pane windows with double-pane LoE glass, front door, and more.
My question… While I have this side down to the studs, what should I do to better insulate the home? Currently, R13 fiberglass insulation is in the walls + 3/4″ styrofoam board (backing for stucco). Is there another product to up the R-value in-between the studs? How about rigid-foam board (R-5) on the outside of the sheathing to remove the thermal bridge?
Certainly those would be an improvement, but is it worth it? Understandably somewhat of a subjective question. Looking for some feedback and other items I should consider when weighing my options.
Thanks!
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Hi Fulton,
My guess is that your building inspector probably calls for R13 in walls in your area, but the 2018 IECC calls for R20. That's what I'd shoot for, which would require a combination of cavity insulation and exterior rigid foam. Whether to replace the existing fiberglass is a question worth considering. The first thing you could do is inspect the installation. Fiberglass is notoriously difficult to install in a way that it will perform up to its stated R-value. Check out this post: https://www.greenbuildingadvisor.com/article/installing-fiberglass-right
If you decide to upgrade, you can search this site for info on all of the options. And keep in mind that air sealing is super important. If you are installing structural sheathing, you could do your air sealing then or you can use the rigid foam for your air barrier (or both, if you would consider ZIP R). Here's some info on exterior air barriers: https://www.greenbuildingadvisor.com/article/airtight-wall-and-roof-sheathing
Is it worth it? Well, if you are asking from an economic perspective, that answer would require energy modeling. From a comfort and durability perspective (and perhaps a conscious perspective), yes, it's worth it.
Fulton,
Putting extra insulation between the studs does little to increase the overall R value of the wall. You can fill the wall with R21 spray foam and still only end up with an R10 wall (vs R8.5 with batts).
The existing 3/4 of foam is pretty good, if you want more there is nothing wrong with bumping that up to 1.5".
In zone 3 I doubt it would make enough of a difference to be worth it. Even up here in zone 5 something like a front wall with a lot of openings (doors/windows), the R value of the whole wall assembly is more effected by the window choice than the insulation.
The more important part is to do a decent job with air sealing your new windows and taping the seams on the existing sheathing.
Thanks for the feedback! I've contacted a local insulation company that will perform an energy audit on my current system and make recommendations on how it can be enhanced. My exterior contractor will be installing the the Zip R system (R-6) instead of OSB + housewrap. This + the new windows, we would expect some worthwhile performance gains.
Something to consider:
In terms of thermal comfort and energy efficiency: depending on how much and what orientation your glazing is throughout your home, in your climate exterior adjustable shading can be a good direction.
Peter