Window flange + EDPM gasket
Watching the Feb 25 BS*+Beer show with Peter Yost discussing applying car gasket technology to window sealing, got me thinking about using EDPM D-shaped sealing gasket as the seal under the window flange. Peter did some wing-nut testing of a mocked up window frame pushed against exterior trim, sealed between with edpm gaskets. He mentioned the Pella steady set system in regards to window manufacturers taking more ownership of window installation systems, but not how the Pella system could take advantage of EDPM seals.
So i wanted to get anyone else’s thoughts on using edpm gaskets in place of caulk under the window flanges.
I am thinking using something like:
https://www.trimlok.com/rubber-extrusion/epdm-seal/d-profile/119-series
Since the flanges on the steady set windows are not nailed through, they seem like a good match to using gaskets. The flanges would still be flash taped back to integrate with the WRB as normal. And spray foam would still be applied between the window and interior framing.
A couple of advantages i can think of:
The edpm gasket should maintain a good seal over time, even with seasonal wood movement. As a side note, i have wondered how a blower door test would fare over time as things move, and maybe some sealants open up.
I feel like a gasket seal would be less prone to imperfections in that seal than applying caulk.
The edpm could be adhered before the wall is stood up, reducing the labor done on a ladder (applying sealant) during window install.
Easier window replacement in the future, and less likely to damage the flashing tape.
Cons:
Caulk (around $.30 per foot) would be a little less cost for material, compared to edpm gasket (around $.50 per foot). Much less wasted packaging and less mess with EDPM. I feel like caulking would be more labor time.
This doesn’t strictly adhere to Pella’s installation instructions.
Some things i’m still working out:
Top corners : Trying to turn the edpm around the top corners would likely pucker too much. Maybe it’s ok to have a separate length across the top, and just butt the side pieces up tight to the top piece. Another option would be to v-notch the gasket at the top corner, but this seems a bit fussy, and may not provide any better result.
Bottom of window : Use a thicker gasket along the bottom of the window (towards the inside of the window frame) as a back dam. Would have to contend with the shims under the window. I would sill slope the sill to the outside. If i do this, should there be any attempt to integrate the bottom seal with the side seals.
Tracy
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Replies
Tracy,
I like the idea a lot. It's already something many people do with skylight curbs - but I have to confess I'm not entirely convinced either sealant or gaskets adds much to a window installation.
How you detail it depends on the goal - which I've never been entirely sure of. If the barrier between the flange and whatever wraps the RO is primarily to stop air movement, then continuity between the jambs and sill becomes important - and I'm not sure how you make an effective transition from the exterior inwards there. If it's to resist water intrusion, the laps at the intersection of the head and jambs should be designed to shed water laterally.
I do feel like sealant under the flange is a hold over from when 'best practice' window installation was to caulk behind the flange area, nail through the flange, and call it a day. But i can see a redundancy added by sealing behind the flange in case any water that gets past the flashing at the top or sides of the windows might be diverted to the sloped, flashed sill.
There is a lot of energy devoted to sealing a home, and then the bottom flange of a window is left unsealed (with good reason), relying on the spray foam, caulk and/or taping the inside of the windows to get an air seal at the window perimeter. It seems none of these methods are reliable for the long term.
So back to my real goal, which is to provide a reliable air seal around the window, without risking trapping water at sill. If i could get a reliable, repeatable method to provide that continuity from the jamb seal to the seal at the back dam, that would be good enough for now.
Someday, i could see window manufacturers adopting a modular window system (some thing Peter Yost alluded to should happen), where a bullet proof frame is installed in the rough opening, and the window is set and latched into the frame from the inside, sealing to the frame. The frames could be unique to specific wall assemblies - exterior insulation, rain screen, siding type, interior and exterior trim, etc. And the windows would be common, and replaceable/upgradable without disturbing the interior or exterior finishes. All while maintaining maximum opening (minimal rail and styles).
Tracy,
What you describe in your last paragraph would be fantastic. It brings to mind Ted Benson's work disentangling the various components of building to make replacement more logical.
warranty preservation aside, epdm gasket might be finicky to install. most windows require co-planar installation so you'd need to ensure that you got equal compression around the edges. otherwise you could warp the frame in the opening if you screw harder on one side than the other. with the redundancy of sealant behind the flange and tape over the flange onto the frame, it seems like the top and sides are sealed pretty well. there might be limited advantage to the bulb sealant [except for making the install a lot more pleasant and less nerve-wracking.]
getting good continuity from the sides to the bottom is really tough with a conventionally framed wood opening. there's not enough room at the bottom to do a good tie-in. if window manufactuers made the bottom flange 2" tall then there would be working room to reach in and tie into the back of the flange after install. as-is, it's a blind tie in.
The Pella steady set system does not use fasteners through the flange, which is why i think their windows would be better suited than nailed flange windows to sealing with a gasket. I am planning to use the steady set windows in my home build this summer, so may try to use gasket seals.