I will be installing new wood double hung windows this spring. They are Wood frame with a cedar sill and five inch flat stock casing pre-attached. The jambs of the window extend past the bottom of the sill at its lowest point, so when they are sitting in the rough opening, there is about an inch or so of daylight between the lowest point of the cedar sill and the rough opening. The guy who sold me the windows says to install them like that, side it, and fill the cavity with foam. If I do that, why build a “sill pan’ with ice and water shield? Won’t the foam trap any water that gets back there? I’m thinking I should cut the jambs so the window sits lower and the low point of the sill is below the rough opening. What do you all think? Thanks for all the input.
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I would leave the jambs the way the seller recommended. Hacking those up may void the warranty.
If you have water getting behind the siding, you will have worse problems to worry about.
Woody, I think this is a great question and predit it will get a lot of responses. Almost any window will leak at some point in it's career. Most leak pretty regularly. Siding instalations leak too. Enough to create the recommendation that the water shielding methods be used. The latest issue of JLC has an article by Joe Lsiturbek about the subject. He has done a lot to educate this industry about drain planes in walls.
I use the foam in the location mentioned and would not recomend cutting off the toes of the jamb but the question raised is pertinent. I may have to rethink that procedure. The whole process of making the wall system to handle water is to provide a way for it to escape without finding a way to get deeper in the wall cavity or becoming trapped within. The foam under the sill could do just that.
The solution that comes to mind right now is to use scrap fibreglass like we used to do near the outer part of the wall and then put foam in. That would let moisture bleed through it to escape..
Excellence is its own reward!
Thanks for the responses so far.
Yeah Piffin, it doesn’t seem to make much sense. I am building the sill pan by ripping some cedar siding, nailing it to the rough sill, the cover with the ice and water shield. Not having installed new wood windows before, I assumed that the sill on the window would sit a lot closer to the rough sill. The fiberglass batting is a good idea, but are you saying to stuff it in for an inch or so then foam the rest of the way back?
Other people must run into this, what do YOU do? (or is everybody into vinyl these days?)
Thanks again
For the most part, vinyl is a four lettre word here.
But for curiousities sake, what brand of window do you have and why did you choose total wood instead of clad?.
Excellence is its own reward!
The windows are manufactured by Boston Sash and Mill. I went all wood to match the other windows on the house. And I like wood. They come factory primed, so with a coupla coats of good quality paint, I should be fine for many years.
Or not.
Pif, I agree that at some point, window (and door) protrusions will leak.
So lets take a close look.
Where do they seem to leak the most.
1) head trim (flashing)
2) siding seams at window trim
3) inside unit i/e sash/sill
4) any others?
Vinyl flange vs wood trim (I know how we all feel about vinyl, however the vinyl flange with good sealant seams like the best theory for keeping transient water at least o/s of the paper)
Thanks
When I say that windows leak, I really didn't mean the seams between window and siding or at the head flashing, but you really do have to include the whole system in the discussion because manufacturers always want to push blame for leaks on the installers and often rightly so but the windows themselves leak pretty regularly too. I think probably far more than half of window leaks are at flashings etc, from bad installations but with many clad windows having nailing flanges, the welded corners are not always perfect.
With wood windows, it is at the junction of sill and jamb and that is where you will find rot in as little as ten years on newer windows.
Part of the problem is that the wood that is grown and harvested today is not as good as what we had even twenty years ago, let alone a hundred years back. Another thing is that the govt made the manufacturers pay attention to VOCs in the factories and they all went to water based preservative/sealers for the wood they use now. Then, faster production rates demanded to keep up with the competition means that the pre applied primers needed to be latex instead of oil. It lays on top of the wood instead of penetrating.
Unless I am imitating and matching old windows in a house, I don't like wood windows anymore because of all the above. When we build custom wood windows to match, I really worek hard to find the right wood, and it isn't fingerjointed fresh grown pine..
Excellence is its own reward!
DO NOT CUT THE JAMBS. By keeping the sill off the base of the rough opening, any water which enters the wall (like piffin said, water will get in at some point)can't saturate and subsequently rot the sill. Plus the airspace formed allows any moisture to dry. If you are really worried about trapping water with the foam, there are two things you can do. One would be to put three rods along the base of the r.o. left, middle and right and then foam. As the foam hardens remove the rods...instant weepholes. Or, case out the inside of the window then foam from the outside with a polyurethane foam but only allow the EXPANDED foam to fill half the depth of the wall. The poly foams are waterproof so any moisture will run down the jamb sides, over the foam if necessary and out the front of the of the r.o. and the foam will seal to the casing to keep out the dreaded drafts. Good luck.
Richie