Replies

1. 
   creativedestruction | Nov 04, 2020 07:20am | #1

   Frame the rough opening a little bigger for more shim space if you're concerned. The primary air seal doesn't have to be deep in the cavity, it just needs to make full contact with the interior of the rough opening. Use the right size backer rod at a consistent depth for a nice 'hourglass' shaped caulk bead. Or use low-expansion canned foam. I'm not as seasoned with acrylic tape installation but there again the seal occurs all the way to the interior however you can make good contact between the frame (or jamb extensions) and the rough opening. Make sure the jamb extensions are airtight to the window frame before installing the window.

2. 
   smac355 | Nov 04, 2020 08:48am | #2

   Thanks Jason - good point on the jamb extensions being airtight, since could be difficult to get the seal directly against the window frame and rough opening if the jamb extension is leaky i would still have issues. May just be more prudent to have our builder install after the fact, but the efficiency is obviously preferred. It would seem like low expansion foam may be best since can get a smaller needle into the opening and closest to the window frame.

1. 
   jberks | Nov 04, 2020 01:52pm | #3

   Hi Sean,

   I'm not sure I understand your method, thus not sure where the concern is. I don't see how caulking and taking is any different with jamb extensions or not.

   My process:
   Usually you slope the sill. water proof/integrate the rough opening to the WRB with acrylic tape. Caulk the 3 sides of the flange if you have them (not the bottom). Install the window (with extensions or not), level & plumb with shims. Screw in place. tape the 3 sides of the flange to the WRB (not the bottom), then airseal the gap from the inside between the window and rough opening with foam. I like canned foam vs backer rod just cause nothing's perfect and don't want to keep all sorts of backer rod around. I try not to overfill the joint so I can later use the expanded and cured foam as a backer rod and then I use a poly urethane sealant to backdam. A Bit overkill with backdamming, but it's not that much work so I do it anyway.

   Jason had an interesting point about airsealing the jamb extension joint..if you get them installed at the factory, you can wrap tape around the outside of the joint before installing the window if you really want. I would just fill the whole joint with canned foam. If you install the jambs in situ, just ensure the carpenters are liberal with the wood glue to form a good seal.

   Hope I'm making sense here,

   Jamie