Doors and Windows - Siding foam & window flashing integration

Changing out all windows. First time DIY. Will re-side after that to cover my tracks :mask:

Contractor will install commercial grade vinyl over 3/4" XPS over existing, freshly primed T1-11 which will perform the sheathing / OSB funciton in the new wall.

For the windows I am using Joseph Stiburek's "WINDOW WITH BUILDING PAPER ON OSB OVER WOOD FRAME WALL" as a general model:

http://www.josephlstiburek.com/resources/windows/Window_OSB_building_paper.pdf

I plan to deviate from this model at Step 9 by not putting up any building paper all around the walls. I expect to hand over to the contractor who will put up the insulation board underlayment and the siding.

SPECIFIC QUESTION: I will be installing a building paper apron at the bottom of the window. The contractor can drape this apron over the insulation board (at the bottom) or can tack the board on over the apron. Which should they do?

If they drape the apron over the board then the bottom window flange is only covered by coil stock or whatever trim they use. Does this cause an air freeway since I will be leaving 1/4" under the vinyl windows for expanstion / contraciton and drainage or is there some other thermal penalty? Is there really any benefit in doing this? It's a bit of mixing of drainage plans although the current arrangement is very "pot luck"!

If they just go over the apron that I left them then, theoretically, any fluid that does penetrate the window area and drains down would run behind the foam at that point although foam over T1-11 suggests that this will be happening all over the place so any issues with foam preventing drying would be across the structure.

Am I getting too detailed? As I mentioned, this is trully a first go for me and I'm feeling the tension :coffee:

I would recommend that the windows be installed on top of the 3/4 XPS foam. If that is not possible due to the fact that YOU are installing the windows and a CONTRACTOR is installing the foam, then I would suggest that once the windows are torn out (before step 3) you install some strips of 3/4" plywood that are roughly 3" or 4" wide- installing them around the perimeter of the rough opening like a frame. This will shim the windows out to the same level as the 3/4" foam (that will eventually butt up next to it) and would give you something solid to nail the windows to. An added benefit is the solid nailing area it would provide around each window... nice if you plan on installing any wood trim around the windows.

I skip Step 6 on your PDF. I feel it's pointless to caulk (as shown on step 7) on top of paper that air could get behind. Additonally, I feel that air can possibly follow the building paper into the home when that technique is used. When that technique is used, insulation is sandwiched between the window and the building paper. But if air comes behind the building paper, and the edge of the building paper happens to be beyond the insulation, air will bypass it. It's been my experience that this is the case. Additionally, I don't like their steps 10-12. IMO, self-adhesive membranes should be installed directly from the nailing fin onto the building paper. But since your contractor will be putting on XPS foam, you won't be following those steps anyway, the way it sounds. Normally the building paper is installed prior to the window installation, making steps 10-12 irrelevant and backwards.

You mentioned a 1/4" gap behind the window. I have NEVER left a vinyl window loose, I have always caulked them in and screwed them snug. You obviously don't need a fastener in EVERY hole that they have provided. If you are planning for drainage out the bottom of the rough opening with a sill pan, you could caulk the top and sides but leave the bottom uncaulked... or perhaps just leave a couple spots uncaulked. In reality, the caulking is also a mute point if a self-adhesive membrane is installed over the nailing flanges.

Once the foam is installed around the windows (that you have installed on top of those 3" or 4" wide strips of 3/4 plywood), I install a self-adhesive membrane down the sides and across the top where it calls for "flashing" in step 8 of your .pdf. The peel and stick membrane would seal the nailing flange of the window to the foam, making it air and water-tight. This of course is provided the seams of your foam are sealed with tape, and that no water ever leaks behind the foam from above.

Back to your specific question, I think it's irrelevant if you build the window out 3/4" to be level with the foam, as I suggested above. If it was me, I would not use building paper on step 3. Unless you are covering all the foam with building paper, I would instead use a strip of self-adhesive membrane there. I would only remove the paper backing on the top 2", and leave the paper on the rest of the membrane. This way you can wait to peel it off until the foam is installed behind it, and when you do peel it off, it will stick to the foam sheathing. If you decide to use building paper, I'm sure it will work fine.

Just a note, if you are going to use any self-adhesive membranes, be sure you do not use tar paper for any of these steps. They do not stick to the tar paper for long before letting go. (usually less than 24 hours.) Sorry this is so long. Something got into me. :mask:

First let me say: WOW. The true voice of experience. Thank you.

Secondly: BUMMER. This massive DIY (in my view!) seems to have been snatched from my trembling, expectant hands at the very last moment! I was *really* pumped up to do this but I just got a final quote back from my siding guy and he pitched $100 / window. I was "afraid" it might come to this. That price is only *slightly* more than I could do it myself (+ windows, tools, flashing, etc.). I'd gotten quotes up to $1,000 per R.O.! Anyway, wifey is truly relieved. If the details check out with these guys then I will reluctantly set down the hammer on this job.

Thirdly: PHILOSOPHY. Your comments are interesting and clearly took some small bit of time to type out. In the end there is an outside chance that I may still do this job but I wanted to comment on your feedback in any case.

- Agree that windows should be on top of the 3/4 XPS. I was thinking of furring the RO under the flanges so am happy you made the suggestion. I like the nailing surface better and it's a much tighter integration.

- Step 6 / building paper on jambs - I also felt this was a bit weird. My only thought was that since the underlayment (T1-11 in this case) is so old that it provided a slightly improved surface but your point is taken. What is its intended purpose in the

- Step 7 / flange caulk - I assume if you didn’t paper the jambs then you would indeed caulk behind the flanges as a precaution. Again, point taken about creation of an airspace.

- Steps 10-12 / applying felt after windows - I obviously would prefer it another way around but since I was planning to have to do the windows myself I needed some kind of scheme to follow.

- 1/4" gap behind the window - I meant to say below the window, essentially the drip pan space. The rest of the window would be shimmed, caulked, foamed, fastened... just the drainage would be open.

- Flashing of foam to window - Even though the foam will be taped (I've seen their work and this is one of the reasons I am using them) I cant promise a complete barrier just based on the construction of the existing house so one can assume fluid moisture will get behind the foam. The lateral interface between foam and T1-11 should be rough enough, IMHO due to the pre-existing inconsistent surface of the siding, that it will stand off the foam enough to provide a plane. Maybe wishful thinking but this is what drives my thinking NOT to require the contractor to further flash the frame up against the foam, given that the rest of it is done right :o

- The actual question (draping the apron over the foam) - I'd take your word that it is irrelevant which is why I wanted to know. I'd "fur" the window by 3/4" to level it with the foam. Building paper wasn’t my first choice but I am not doing it over all of the foam. In using a self-adhesive membrane at the base what would the top 2" actually be flashed to? Under the flange or ? I just cant visualize this. Ultimately I also thought that there was no harm in using the building paper either.

- Tar paper / self-adhesive membranes interface - you say that these don’t stick together well. Isn’t building paper also called tar paper? Are you suggesting to just use strips from short rolls of Tyvek?

Thanks for everything again!

First, glad to try and help.
Second, maybe you can still work along with the guy, if nothing else, to gain a little experience and hands-on.
Third, thanks for the feedback. It's nice to know that the time we take to try and help is appreciated.

To answer your further question: The terms building paper and housewrap are thrown around quite a bit, and when you say "building paper" you might think of any of several products you could use to cover the building. In the olden days, it actually used to be made of paper. Some older houses have a sort of cardboard sheet that covers the sheathing to protect it. Others have felt or tar paper. Nowadays there are various types of "housewraps" that come in large rolls, and are viewed to be an improvement over the old standbys. When you use the term "housewrap", most people think of the newer products like Typar, Tyvek, and so on. Really they are all "building paper"... something that protects the sheathing in the event of leaks.

In most cases, if I'm only flashing around a window a little ways, I will use a small roll of Tyvek. Tyvek usually comes in 9' wide rolls. But when we have just a little bit left on the roll, I'll cut the entire roll on the radial arm saw to create little 12" long rolls, which work really nice for papering a rough opening.

Thanks again.

HD has some shorty roles of Tyvek which seem a lot easier to work with, your right. Would have went that route.

Working alongside the guy? I guess I'll throw it out there but I'd be surprised if he didnt charge extra! )

Ultimately I'm going to have to get my hands dirty anyway since I have to remove old storms (inside versions) across everything. They are VERY well sealing as the are patched right into the drywall returns. In fact they make up the corners of the interior jambs and head (caulked across the sill) so I'm going to have to cut 1/2"+ in from the corner to get them out then I'll remove the 2" remaining drywall between the storms and the old alumininum window frames which will expose the RO from the inside. Of course I'd have to get this out anyway so no extra work overall. Actually these storms are pretty neat and I'd like to try and sell / give them to a "good home" (I have a horrible green / recycle steak in me).

However, I think that I have milked this thread for all it is worht and want to thank you for your input. Will persue the last bit under a separate avenue.

- Jonathan