Innie or outie windows with exterior foam?
Svig
| Posted in Energy Efficiency and Durability on
CZ 7 Northern MN, 2×6 standard frame with 4″ exterior foam. Exterior foam is basically unknown here. My builder and the local lumber yard person think I should go with innies, because they both feel the windows would get too cold being on the outside of the wall. My windows will be Marvin double hung, fiberglass or aluminum out, wood in. I had thought I would go with outside windows because I thought it would be easier (cheaper) to extend the frame inside, than extend the trim outside, but I am not stuck on either one. Thoughts and comments appreciated.
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It's true that the thermal performance is best with the windows near the middle of the overall insulation depth. With a US window, installing it as an "innie" with your construction, the glass ends up roughly at the outside of the 2x6 wall, which is closer to the middle than it would be installed as an "outie".
But I think the most important factors are:
1) Getting the flashing and WRB integration details correct,
2) Getting the air sealing done well,
3) Doing all that without having the builder spend a week fussing with each window to figure it out and thus having the labor cost go through the roof.
All three are most likely optimized by going with what your builder is most comfortable with. But verifying all those details is important given that it's going to be new to them regardless.
My preference was to place the window in line with the air barrier/WRB.
In terms of energy efficiency, I suspect you would see a greater difference if you installed casement windows instead of double hung.
Steve,
There are benefits to each configuration. I agree with you. I think the outside windows look the best, and are probably the easiest to do for the inexperienced--just extend the window bucks, integrate the WRB and air seal like any other new window installation. With outside windows, it is also easy to use casement windows (See my article on this website under the Green Homes tab). A lot of people are stuck on double-hung windows, but casements seal better. they look great, and when it's time for opening them, they open big. On the inside, a wide sill is nice. In my case, that wide inside sill/casing works well for the installation of Comfortrak thermal shades.
The only benefit I know of for the mid-mounted windows may be a little better energy efficiency but I'm not sure that claim has been well substantiated. Even if it has been, I doubt if that mounting scheme does better than using good casements on the outside.
There is an article about this aspect of window placement somewhere on this website.
I would do "innie" Windows and integrate your window and flashing with the WRB. BUILD YOUR EXTERIOR EXTENSION JAMBS IN THE SHOP. Install as many of the same size Windows as possible to facilitate the ease of creating these exterior trim sets. Remember by doing this install, you need not build custom jambs, you can order your windows with factory interior jambs in 2x6 format. You get the ability to shelter your windows from the elements. Your exterior trim can be pre made and hung, perhaps even using some trim screws to hold them in, so to facilitate window replacement in the future should you get a broken or defective window. Remember that the job of the trim is not really keeping the water out completely because the WRB is beneath the foam and trim. I would also be inclined to (once you put your foam up) to do a second wrapping of house wrap over the foam, to tape and flash onto at the window openings under that trim. A little more money but a LOT of insurance.
If you like the look of double hung over casement, consider some of the different simulated divided light options. This pattern,
http://www.marvin.com/images/integrity/product/features/Integrity-Windows-Wood-Ultrex-Casement/Integrity_Casement_26.jpg
sometimes called "cottage," gives some of the look and feel of double-hung, while actually giving a clearer view. We did that and love the look and get compliments from visitors and neighbors alike, even though they don't know that it was originally motivated by energy efficiency. (Ours aren't from Marvin--that was just a convenient picture to link.)
Thanks for the advice everyone. I am still unsure how I will go. My carpenter and I are going to do a mock up of an innie to see how it goes. (when I get back to CZ 7, I am currently in Florida!) My better half is certain we are going with double hung,... so certain, I don't even bring it up any more.
I ordered the casements in the exact configuration that Charlie linked to, with triple glazing everywhere but the direct Southern exposure. The fiberglass Integrity line is very good.