Adding Exterior Insulation Without Replacing Windows
user-7392816
| Posted in General Questions on
We are embarking on adding a new addition to the home and decided this may be a good time to add exterior insulation since our home gets an enormous amount of direct sunlight translates to interior radiated heat since our walls are only 2×4 with R13 batts. All of the contractors we have contacted so far have only done this by installing new windows moving them to the outside of the insulation. While this makes perfect sense it is quite cost prohibitive and wanted to know if anyone else has tackled this without removing and re-installing windows?
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> We are embarking on adding a new addition to the home and decided this may be a good time to add exterior insulation since our home gets an enormous amount of direct sunlight translates to interior radiated heat since our walls are only 2×4 with R13 batts.
Exterior insulation would certainly be helpful, but if you think radiant heat is your concern, a lot of your cooling load could be coming via radiant heat through your windows.
Radiant energy won't get 'through' your walls. However, radiant energy will heat your exterior cladding which will then heat your house by conduction, but I expect this effect is much less than the radiant energy coming through your windows.
Knowing your climate zone, type of exterior cladding, and type of windows can help provide a 'gut check' on where your energy loads are. There are also tools like BEopt that can help model it with some accuracy.
> While this makes perfect sense it is quite cost prohibitive and wanted to know if anyone else has tackled this without removing and re-installing windows?
There's no doubt it can be done, but you have to have a clear and consistent idea of what your drainage plane is and detail it accordingly.
I think knowing whether or not it is radiant or conductive is key. Outside of the simulated Manual J load calc, are they any ways to empirically measure the two to see which one it is? I was thinking about picking a room and adding temporary insulation covering the window and then taking measurements throughout the day versus the samples already captured. But is there another way?
The ease of this will depend on how much foam you are looking to install. If you're talking just an inch or two (see the code requirements for exterior foam in your climate zone - let us know if that's a confusing statement) it's not a big deal. I've seen it a couple of times but couldn't drag up a detail quickly. Here's a video showing one approach - they are installing new windows but inside of the foam layer so it's still reasonably applicable to your situation.
https://www.protradecraft.com/exterior-foam-insulation-retrofit-how-install-polyiso-panels
It will require the replacement of your bulk water barrier, re-flashing windows/doors, etc.
I suppose you could essentially convert your windows to "innies" or "inbetweenies" while leaving them in place. Flashing and trim might get tricky, and obviously the thicker the foam, the trickier everything gets. The general rule is over 2" is "tricky", but in your case, trying to leave existing windows in place, my GUESS is that 1" or more starts to get "tricky". I can't claim to have ever tried this though, I would normally recommend just reinstalling the windows (or replacing them, depending on the scope of the project).
Since adding exterior rigid foam pretty much requires a reside anyway, how hard would it be to just do it the "right" way and build the windows out a bit on bucks while you're doing the rest? Hanging a window isn't usually a huge deal unless you have to reframe the opening to a different size.
Bill
If I were to do a reside I would redo the housewrap, which would mean redoing the flashing around the windows. I guess it depends on the window attachment style but I would think that if you're doing all of that it wouldn't be much more to remove the fasteners holding the window in place and slide it out a couple of inches.
I realize that you always want to manage "scope creep" and if you take the windows out you've gone from a project that is exterior-only to one that at a minimum involves removing the interior trim and then reinstalling it and repainting.
More detail about the window style and how they are attached would be helpful.
If you don't have modern windows with fancy coatings, that is the place to start. The low e coatings will cut the heat from the sun dramatically.
If your windows are already properly flashed, your WRB is in good shape and of good quality then you already have "innie" windows. Then you strip siding, add foam, furring and cladding. The finish trim requires jams to cover the depth/projection of the foam.
+1 for Tim R's suggestion. Decent low e windows made a huge difference in felt summer afternoon solar gain on the west end of my house.