Windows for Double-Stud Walls
currently considering a 12″ double-stud-wall in cz-6 and noodling with window options.
one option would be an outie (flanged or euro), which would have the benefit of avoiding extension-jambs, but would have the drawback of lack of shelter from the elements, and being on the thermal-exterior.
another option would be a middie-euro which would have the benefit of some shelter from the elements and being in the thermal-middle of the wall, but require extension-jambs.
1. i know there is some religion, but always interesting to get a point-in-time informal survey on if the thermal placement of outies is enough downside to incur the fussiness (and even risk of not getting right) middie detailing.
2. assuming the middie route, with a 4″ setback, a 4″ thick window casing, and 4″ to interior, to account for a sloped-sill, should i be considering:
(a) an 8″ wide piece of beveled siding to cover the distance from the back of the casing to the sheathing, or
(b) try to slope the entire bottom 12″ rip, or
(c) other?
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Replies
One additional factor I consider when faced with this decision is whether I want the shadow line that recessed windows provide. Traditional architecture is full of shadow lines that bring a facade to life, whereas most (or at least much of) modern architecture is flat, planar and relatively lifeless.
Performance-wise, it requires a sophisticated modeling program like the ones used for Passive House to determine the energy impact of the built-in shading that recessed windows have, but in CZ6, I'd estimate the order-of-magnitude difference on an average project to be in $5 to $50 per year range for the entire house, or $0.10 to $2.50 per window per year. There is cost in creating exterior extension jambs and sills, which would likely never be fully recovered if you are thinking of it only in terms of energy savings.
Getting the detailing right for an outie is not as simple as you might think; you need a fully integrated buck, and to consider the depth of the rain screen you should be using, interior extension jambs and stool caps, exterior maintenance of an outie vs. an innie, etc.. I often end up going with innies (or in-betweenies) and using fin jambs on the exterior--extension jambs with no additional window trim, which looks modern and saves a little money.
Your second question depends on a few factors. Are you using flangeless windows? What do you want the sill extension to be made of, and how thick will it be? With double stud walls I always use 3/4" sheet goods to make bucks connecting the inner and outer stud walls, and I often use a 2X spacer below the window to get additional slope for the sill extension.
good points michael
1. i was trying to simplify the structure itself along the pretty-good-house principle, so the extra dimension of recessed windows could really help the aesthetic of the exterior.
2. i wasn't thinking so much of energy-cost, but steve baczek talk of micro-climates made me think it would cause window failure or something. if the downside is really only a few bucks in efficiency, then it's a non-issue.
3. i haven't decided on the windows yet, so trying to understand the implications of either flanged which would be outies (and i have a good handle on how that detail would go), or flangeless euro which i'm trying to grok the implication. are there techniques for euro windows mounted flush with the sheathing so they are like pseudo-outies not requiring extensions? i'm also going for low maintenance, so if i do end up recessing, would want exterior extension jambs to be made out of something like composite. would use sheet-goods for the internal bucks too. any links to relevant reference drawings would be helpful.
Lot of window manufacturers offer exterior extensions profiles that are longer. These are usually used for sills be can go all the way around as well. I would find out what you can get and design from there. Any exterior jamb that is not composite or metal will not hold up in the long run, I would avoid any design that uses anything wood that is painted. The lack of shelter on modern windows is much less of an issue than older wood windows. Plus having done exterior extensions, it is a lot of extra work.
I'm a big fan of outie windows as you get these great deep window sills, they make the windows feel larger on the inside and a great place for plants.
yes, akos, i've seen some manufacturer provided exterior extensions from companies like duxton which would be great. completely agree on the composite or metal, low-maintenance is high on my priority list.
good to know that shelter isn't as important as it used to be, and also that exterior extensions are significant effort. i imagine they would be times dozens of windows, it's definitely gonna add some labor. i'm ok with the labor cost, is long as there is a reasonable path to get it done in a failure free way.
i also like the idea of deep sills, so have to find some happy balance of all the things.
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I did some in-betweenies and while flangless windows don't need the 2x ring all the way around, I still placed my flangless on a 2x (placed on a tapered base) so that the sill extension could have enough slope (i was shooting for a more traditional 14 degree). With a plywood buck i sloped the buck a touch for drainage which gave the 2x slope as well. Extoseal encors for pan flashing, up onto the 2x. Boral extensions assembled as a frame as mentioned above. Attaching these was a bit finicky for sure and probably not the most robust thing in town. I like the depth Michael mentions, but one downside is that outside debris collects on the sill extensions and they never look clean.