question for installers - sill plate membrane/sill pan

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Will91
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question for installers - sill plate membrane/sill pan

#1 Post by Will91 »

Hello:

I have 2x4 wall construction and interior "drywall returns", ie no interior wood trim other than the wood window sill and apron.

I'm having siding and trim removed and new housewrap integrated with my new Simonton windows with integral nail fin flange.

The Tyvek book I saw shows using membrane such as DuPont StraightFlash (or Protecto Wrap) placed horizontally on the sill and wrapped up a bit each vertical side. Is this what most of the pros are using here or are you using some sort of premade sill pan such as the Dow sill pan or JamSill products - or a combination of both? I think just a quality sill "pan" made of membrane flashing is fine, but the only thing I don't like is that it doesn't have the rear up-turned "dam" like some of the plastic prefabricated sill pans.

Any input appreciated.

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Delaware Mike
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Re: question for installers - sill plate membrane/sill pan

#2 Post by Delaware Mike »

That's where the low-expansion spray foam comes into play under the new window. The window should sit up on top of several shims. I really like Dupont's flex wrap for the sills. You can see videos on Youtube on the correct application just by searching.

Will91
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Re: question for installers - sill plate membrane/sill pan

#3 Post by Will91 »

Thanks Delaware Mike:

I'm going DuPont products all the way - including their Weatherization Sealant Caulk, just to be sure everything is compatible.

I don't think the low expansion spray foam will be possible without removing the nail fin (which I don't want to do) or removing the intact drywall returns. From what I understand, and I hope I have this right, water infiltration is addressed by nail fin caulk and membrane flashing, and the foam acts more for air infiltration/insulation that true water protection. IF I have the windows cased out with wood, this would be the only way to get the foam in and I think I will leave the drywall returns as is - to maintain a more contemporary look of the home.

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Windows on Washington
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Re: question for installers - sill plate membrane/sill pan

#4 Post by Windows on Washington »

Flex wrap on the sills, straight flash on the jambs and head and you can inject the foam just prior to pushing the window all the way back.

Will91
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Re: question for installers - sill plate membrane/sill pan

#5 Post by Will91 »

Thanks.

WOW, when you say to inject the foam before pushing the window all the way back, do you mean foam can be injected with a nail fin flange window from the exterior of the home? I thought the only way to do this was to install the window (with caulk on the backside of the fin flange) and then foam from inside the house (provided that that drywall etc. is already not installed). Since my drywall returns are already in place, I had thought I would have to forego foam insulation but wasn't too concerned since I knew the window would be well sealed by the caulk, membrane flashing, and integration with new Tyvek. Also, do you ever use anything like the JambSill or Dow Sill Pan product along with the membrane (I would think the membrane could go on the sill first, and then a product like this. ) ?? It seems like the upturned feature on these products creates a nice "dam" feature against water.

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Windows on Washington
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Re: question for installers - sill plate membrane/sill pan

#6 Post by Windows on Washington »

I was suggesting that you foam it from the inside prior to the drywall returns fitting over the drywall.

Will91
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Re: question for installers - sill plate membrane/sill pan

#7 Post by Will91 »

Thanks WOW. Any comments/opinions about using something like JamSill or Dow sill pans in addition to DuPont membrane flashing for the sill plate?

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Windows on Washington
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Re: question for installers - sill plate membrane/sill pan

#8 Post by Windows on Washington »

Probably overkill but they are not expensive and you might as well go full bore and do it once.

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