Backer rod & spray foam – windows
I’m struggling to get a decent seal with spray foam around our windows without completely filling the rough opening. We want to leave a small path for water to exit (our sills are sloped toward the exterior).Â
It’s most likely user error, but our contractor has been no help here. I’ve tried OSI Quad and Great Stuff Pro Window & Door.
Is putting backer rod in before spray foaming to control the depth a decent solution to this?
We were wanting to use backer rod and caulk after spray foaming, so we would most likely do that as well. So it would be backer rod, spray foam, more backer rod, and caulk. Other than having to double up on backer rod cost, is there any reason why doing this would be a bad idea?
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You could try backer rod, it will probably work. Another option is to put something in to act as a sort of form to keep the spray foam out, then remove the form later. What I've sometimes done is to wrap small pieces of wood dowel or other scrap with saran wrap (very thin plastic wrap), then apply the foam. After the foam has cured fully (I usually wait until the next day), I can remove the scrap wood piece and just leave the saran wrap glued to the foam. Sometimes a utility knife is needed to cut the form out, but the saran wrap acts as a sort of "release" layer in that it lets you remove the rigid form without having to cut through all of the foam.
Bill
If I go with backer rod, do I need to remove it once the foam is cured? Or can I leave it and just have a spray foam sandwich in the rough opening (backer rod, foam, backer road & caulk)?
I don't see any issues with leaving the backer rod.
Ok, great! Another question - When it comes to caulking the inner-most backer rod, does the caulk need to be applied to the jamb flashing tape and the window? Or does it need to have contact with the wood window jamb? The guy who flashed our sill and jambs wrapped the flashing tape around to the interior, but I'm not sure if this is the best for ensuring a continuous air barrier. Would love to hear everyone's thoughts!
Can you clarify what you mean when you write: "The guy who flashed our sill and jambs wrapped the flashing tape around to the interior" . Does that mean that self-adhering flashing tape was installed as a sill pan over the rough opening sill and tape was also applied over the sides of the rough opening from the sill pan up to the header? And that the flashing tape extends all the way from the exterior sheathing to the inside face of the rough sill at the bottom and jack studs on the inside?
If the tape is indeed bonded to the exterior sheathing and the entire face of the framing then the caulking can be applied between the flashing tape and the frame of the window for an effective air barrier. Since you are intending the taped OSB to be your primary air barrier layer then the jamb and sill tape are the continuation of the air barrier from the sheathing to the inside edge of the window frame. And then the caulking bridging the gap beween the tape and the perimeter of the window frame continues the air seal.
Alternatively, if there were no self-adhering flashing tape bonded to the rough opening framing then the lumber itself can continue the air barrier. In that case, the OSB sheathing must be sealed to the lumber. Often this is done by applying caulking to the outside edge of the lumber before the OSB sheathing is applied. Then the caulking can be run between the rough opening frame and the window frame to make the seal.
Did the guy who flashed rough openings apply self-adhering flashing up the sides of the rough openings from the sill pan at the bottom to the top at the header? If so, did the tape extend onto the face of the OSB?
Reason I'm asking is you asked the question "does the caulk need to be applied to the jamb flashing tape and the window? Or does it need to have contact with the wood window jamb?"
The answer depends. If there is self-adhering tape and it's sealed to your primary air barrier (the taped OSB) then the jamb tape needs to be sealed to the OSB in order to complete the air barrier to the inside face of the window frame where the caulking joins the tape to the window.
Yes, the jamb tape was adhered to the OSB. He only did the jambs and sill, not the header. The sill tape was integrated with the WRB.
Based on that info, what do you think?
Stone wool or slag wool insulation from the back of the nail fin to about 1 in. before the inside edges of the window frame. Backer rod pressed in 1/2 in. back from the inside edges of the window frame. Sealant bead about 1/4 in. deep. Then apply the extension jamb. Fill the space with fiber insulation. Pretty much what Michael Maines suggested.
The jamb extensions are factory applied, so attaching them after air sealing is unfortunately not an option.
They're making it difficult to reach back to the window frame in some areas where the gap is pretty narrow, so the caulk would likely just be globbed on (idk if I can get a tool back there to smooth it out). Will that be an issue?
I can see where the frame and the extension join. I was able to use a flat spatula to get some sealant on that joint to help air seal that seam. It's not perfect, but it's better than nothing.
From where I see the seam, that only leaves about 1 & 5/8 inch of the frame visible. I can't tell if the window frame is deeper than what I can see. So the insulation layer would be very shallow.
Thoughts?
Just bubbling up my previous question. Would love some clarity here!
Spray foaming around windows is common but high-performance builders and architects are changing to taping the interiors, with some fluffy insulation tucked into the installation gaps. There are a few reasons for the change but one is that the foam will hold water if there were a leak. Another is that thin foam is not a reliable air barrier.
Sealant with backer rod at the interior can also work. The backer rod should be placed so the sealant is roughly twice as wide as it is deep, or worst case no deeper than it is wide, near the interior.
When using a draining sill pan, the window exterior needs to complete the WRB (water control layer) and the window interior needs to complete the air control layer. If the WRB is being used as the primary air control membrane, then sealing to it is the right approach. If something else is your primary air control layer, the window needs to connect continuously with that.
Our main air barrier is our taped OSB seams. Our window was installed using the AAMA-B method, so the flanges were taped directly to the OSB, and the WRB was integrated to the flanges on top of that.
I'm having such a hard time with keeping the spray foam from filling the entire cavity (using it for air seal and insulation). The jamb extensions + uneven window opening = a headache for a DIY-er. I'm tempted to scrap it and use some rockwool in the cavities (leaving a drainage gap) like you mentioned and do a backer rod w/ caulk and Siga tape on the interior.
Or slide a backer rod past the jamb extensions and get it back to the window frame itself. Then do caulk at that level. Then I could foam from the caulk to the interior without having to worry about depth.
Thoughts?
I don't think you need both Siga tape and caulking. Caulking is likely less expensive but I think this is a good situation for tape. Rockwool is a good choice for the cavity.
So does the air barrier need to be back at the window frame itself or between the jamb extensions and the rough opening (at the inner most portion of the rough opening)?
Just had someone from Pella suggest using backer rod back at the window frame to ensure a drainage cavity is left, spray foam a little for air sealing (but only between the frame and opening (their instructions specifically say NOT to put it between the jamb extensions and opening).
They then said I could fill the empty void between the jamb extensions and opening with Rockwool and do a backer rod and caulk at the inner most part of the opening.
Any thoughts on this?
Your air seal (caulking or tape) should be between the inside edge of the window frame and the rough opening before the extension jambs are appliled. The main reason to seal here rather than at the inside of the extension jamb is that there will be a gap (small perhaps but still a gap) between the extension jamb and the window frame.
Regarding Pella's suggestion - Use the backer rod but don't use spray foam. I just removed a door In installed 27 years ago and used spray foam. The foam was not bonded well in spots so air was leaking.
Instead install a backer rod about pressed back from the inside edge of the window frame by about 1/4 to 1/2 inch. Then apply a bead of gunnable sealant (caulking ). The thickness (front to back) of the sealant bead should be half the width of the gap between the RO and the window frame. For instance, if the RO to frame gap is 1/4 in. wide then the bead should be about 1/8 in. deep. But if you go a little deeper it's not the end of the world.
Rockwool is a good material to fill the free space between the back of the window flange at the exterior and the back of the backer rod on the inside. And if you want to stuff some Rockwool between the RO and the extension jamb - it won't hurt anything. There's no need for a second layer of backer rod and sealant at the inside of the extension jamb if you do as I note above and make your seal at the window frame.
Replying to tjones1014 #15 comment: I guess since the extension jambs are already installed - and the windows are installed - you're limited to tucking in backer rod and applying sealant bertween the inside edge of the extension jambs and the rough opening. Hopefully the factory glued the extensions to the window frame so the joint doesn't leak.
Ideally with applied extensions you would apply self-adhering tape around the perimeter of the window/extension jamb joint to ensure it's sealed - before the windows are installed.
YOu can only do the best you can given the situation.
I was able to get a spatula in there and smear some Prosoco AirDam on the jamb extension seams. We're hoping that will help.
Is there any concern with trying to use backer rod and caulk back at the window frame AND at the inside edge of the jamb extensions (as a backup in case we aren't able to get a good seal at the window frame - or could use tape)?
So from the nail flange inward it would be rockwool, backer rod w/caulk, more rockwool, more backer rod w/ caulk (or tape)
There are probably other sources of air leaks in the house that are greater than leaks around the windows that will give you more bang for your attention than double sealing windows.
I would rockwool flange to the inside of the extension, backer rod and caulk one window. Then use a blower door or other exhaust fan to create negative pressure - then check that window for air leakage. If it's tight at the extension jamb to frame connection then do the rest of the windows that way.
Any other tips for creating negative pressure for a DIY-er? There aren't any exhaust fans in the home currently (down to the studs), and we don't have someone do the blower door test done that quickly. Thanks!
You can put a box or drum fan in a window or door opening and use cardboard to to fill in the gaps