flashing windows with exter. insulation
Quick question – we’re using bitumous tape to flash our windows, and normally I understand how to lap the house wrap and all that to create a good seal – however we’re doing a house that has 1 inch exterior insulation over top of the house wrap and the windows (therefore) sit proud ~1 inch from the sheathing… so with the wall layers being sheathing, house-wrap, insulation (blocking around openings), and eventually siding, I have my first piece of flashing tape on the bottom of the window opening – should I wrap my flashing tape behind or in front of the insulation? I don’t know why this is confusing me, but it is… it seems to me any water that gets in behind the insulation is going to enter at the window openings because there isn’t a very good seal there at all, especially with the window sitting out the extra inch…
Replies
Just to be sure, you Blocked out you windows to accommodate the insulation thickness,so this means your house wrap was place behind the blocking or you manage to wrap some on top of blocking. If so use the tape from window flange to exterior side of insulation board. all water will then drain to exterior side of insulation, anything that can make it pass that layer will be directed down on house wrap.
Don't forget to have the drip cap flange placed BEHIND the house wrap.
Just to get you started thinking while others get ready to respond--whoever installed the housewrap should have cut "X's" over the windows and folded the housewrap in and sealed it with tape, so that should help some. I agree with you that you don't want water behind the insulation and I would do the flashing over the insulation.
You do know to work from sill, and sill corners, sides, then the header, right? Think like a drop of water--always being led to the outside and over the membrane below.
no - that's true. I guess there is the layer of housewrap helping to keep water out. And like the previous post mentioned, there is the flashing above the window that will be tucked behind the housewrap. That should protect it from above the opening and direct water out and away.
I understand the bottom, sides, top order of things - but my thinking was that presumably those layers need to be in the same plane in order to function properly and keep that water droplet out. If they are all sitting outside of the insulation layer, then water could get in behind - and if they are in different planes (i.e. some behind the insulation, some in front) - you don't have a continuous barrier either and opportunity for water to get in... Maybe I'm just overthinking this... in some ways it's just academic - the actual windows that spearked this thought are tucked under a 2ft roof overhang and won't see much wind-driven rain anyways. But for future projects I wanted to sort out the detail...
Cheers!