There are several good articles on this application.

You can reinforce the buck and make your own extension of the rough opening.

That is how I prefer to do it.

I like the idea of the window sitting near flush with the exterior and also the deeper jamb/sill.

Feel free to email me and I can walk you through how we approach it.

Here is a link that might be useful: Innie vs. Outie

I like to detail them as WW explained. The easiest is to build the RO out, however some argue this does not give you a good thermal break. For 3", you could treat it similar to 2" details I use. One 2", I have them build the RO out with 1" material around the opening and butt the foam into that. then install strips of 1" foam on top of the RO and then install the window, caulking and taping between each layer. 3" could be similar and simply install a 2x on the flat, install 1.5" of xps over that and then your window. Or the simplest was is to just install 2 2x on the flat to equal 3" thickness and butt the foam into that, caulking and taping the joints. I like to caulk the 2x to the sheathing and then install 6" tape flashing (such as DuPont All Weather...great tape) from the sheathing and lap it up over the furred RO to prevent any water from getting behind it. Then install the window to the extended RO. I too do not like innie windows. My walls are 11" thick, with the windows set to the outside so I have about a 7" sill. Love the deep sills to set stuff on. I used pieces of our strand bamboo flooring to build the sills out of.

That's great advice, thanks. Love the idea of using the flooring to match the windows.

I read that article and a could points elude me.
In the outies portion:
5. Windows are installed in the plywood frames; they are attached to the studs (through the plywood) with metal masonry clips (masonry brackets).

I don't understand where they want the masonry clips, the picture does not help.

7. Plastic housewrap is installed over the foam. The housewrap laps over the peel-and-stick flashing. Under the windows, peel-and-stick flashing laps over the housewrap.

My inspector said if i wrap the foam he will not pass me. How necessary is wrap for outies? (climate zone 7 if that helps)

On the innies section:
Should brick molds be removed for innies?

6. The exposed foam under the window sill is cut at a slope and protected with copper flashing.

Copper is the best option or the only one?

7. The exterior of the window is trimmed out with water-resistant jamb extensions made of cedar or cellular PVC.

On person mentions hardiboard for this trim...should work?

Later in the article one expert says "IâÂÂve observed that in extremely cold weather �" when itâÂÂs 25ðF below zero, for example �" frost tends to form inside windows installed at the face of the wall, whereas frost rarely occurs on inset windows."

It gets -40ðC here, maybe i should go innies or halfies.

Full disclosure: My walls are 2x4 studs so with 1/2 gypsum, 1inch shiplap, 2 x 1.4 foam, 1/2(3/4 ?) furring and siding my wall will be somewhere near 10".

Why won't he pass you if you wrap the foam?

In that wall assembly, I would look at a higher than triple pane krypton window.

Have you looked at some of the 5 layer systems?

A triple pane krypton window is going to be a huge hole (regardless of set type) in the thermal assembly.

At -40, you are going to get some frost regardless of window type and set.

any reason why you are going with the wall make up you are? have you started construction yet?

If not, you could simplify your system, most likely reduce cost, and have a higher r assembly if you eliminate the foam and move to a double stud wall assembly. You already have the inner 2x4 wall, and the outer 2x4 wall will cost a lot less then 3" of XPS would. Increase your thickness to about 10 to 12" out to out of the 2x4, fill with cellulose or blown fiberglass, and you have a strong r40+ wall compared to the R25 average wall you are proposing. Then you instll the windows as normal onto the exterior sheathing plane. I highly recommend using Huber ZIP sheathing as well and eliminating the Tyvek or whatever wrap you are using. Double stud walls are very easy to build and eliminate the detailing and drainage headaches of thick foam. I have found once you hit 2" of XPS, the cost of construction sways to be more cost effective per R with double studs.

I think triple pane glazing is a great start (I have it in my own home) and shoot for u around .17 or better. I am still not convinced thicker layer systems (suspended films or more glass) are there yet and the cost/ benefit is scewed. Even upping it to an R7 to 9 super expensive window compared to a r5 triple pane is a massive hole in an r40 wall. Tune the windows for solar gains and high SHGC (the highest I got out of my triples was SHGC of .40 and U of .21) and then your windows could become a net heat gain instead of loss.

I like double stud walls as well.

Just not that many guys doing them or doing them well.

Google Robert Riversong. He has been doing that for years and is really good at it.

I agree with you about the additional investment potentially not paying it self back but with such a high efficiency envelope, every bit counts.

Based on the an average split between Walls and Windows being 80% clear walls and 20% windows:

An R-40 wall with a U-Factor 0.17 windows equals a total wall average of R-18.5. Crazy how much it cuts it down.

An R-40 wall with a U-Factor 0.12 window equals a total wall average of R-23. Raises it nearly 5 points.

Maybe as an alternative you not look at the 5-layer glass windows but perhaps something with an interior storm application that can be easily removed.

BTW, there are some new windows coming out with triple pane argon numbers in the 0.13 - 0.15 range.

Obviously I understand and agree with your point, but dollars need to come from somewhere. Throwing it into an energy modeling project you are playing with dollars saved a year difference in heating costs. Pay offs can be very high in high performance wall assemblies after you hit a tipping point. At this point, more focus needs to be placed on the design, placement and sizing of the glass in relation to the building design, spaces, elevations and overhangs. I also find 20% glazing in a climate like this is way way too high. But yes, valid point to quickly show the dirty secret of windows.

what are the VT numbers on that glass? Has to be very low.

I was told the foam is my wrap, aditional wrap will cause moisture issues.

Stud walls would be a ton of permits as my house would increase size, also i live on an avenue and my home can not be to close to the curb.

On my dieing phone, just touching base. Thanks for all the info.

The perm rating of 3" of XPS will force inward drying of any interior created moisture as its vapor impermeable so you need to omit the moisture barrier on the interior of the stud (if its still a "code" requirement) as well as use low perm paints, and certainly no vinyl wall coverings. Your dew point is in the foam, so you will have very low inward drive from the exterior anyway. However house wraps on the exterior will not affect the vapor drive. Most house wraps are high perm to allow inward or outward drying but shed bulk water which makes it useful in flashing for thick foam assemblies. You can then rely on gravity to help shed water verses tapes, foams, and caulks to keep water out (which would be the case in detailing your foam sheathing as the drainage plane). It can work, have done it, but still prefer build wraps of some kind to flash above the windows at least.

So i should talk to the inspector.

There are plenty of resources online to prove perm ratings of foam, vapor drives, and perm ratings of buiding wraps. Should not be hard to argue the case.

I argue the case all the time with local builders and inspectors. Some of them can be stubborn, but usually when I say "would you be willing to sign a paper that states, if we do it your way, and mold developes, you will mitigate it".
In your case, a building wrap or not will not affect you either way on that front, however if you include an internal vapor barrier (plastic on your open studs under the drywall) then you could be in for trouble.

VT number on that triple pane window is no worse than standard triple pane and it actually uses the higher SHGC range glass from Guardian or Cardinal.

VTs are in the low to mid 40s.

It is more about getting the larger air space in the IGU that nets the better performance out of the standard triple pane window with the cheaper argon fill.

Your inspector is incorrect. Wrapping the home with Tyvek is not going to create a vapor trap as it is tremendously vapor open. Is it an absolute necessity...no. Is it a cheap extra layer that takes some of the seams out of the clad exterior, yes.

lzerarc has got you squared on everything else.

You are absolutely correct that more attention should be paid to orientation and placement. That can have as much to do with performance as quantity.

Good info above. Your inspector is wrong... and btw, that does not mean that he is wrong in terms of code, or what what used to be thought of as correct, but for the reasons very well articulated above, he is wrong in telling you not to use a wrb. It would be beneficial.

This post was edited by HomeSealed on Thu, Aug 29, 13 at 13:29

OK thanks guys! I will try to persuade him otherwise.

Anyone know a good article about the subject in climate zone 7? in the mean time I will head over to building science for a look.

Edit: you guys think this link will be enough for the inspector?

If he can't be persuaded then what?

Here is a link that might be useful: Rigid foam as a water resistive barrier

This post was edited by Noctua on Sat, Aug 31, 13 at 5:54

The foam will work fine as your WRB.

I would still prefer to have some sort of housewrap at the end of the day. Just another layer of insurance and a cheap one at that.