Spray foaming around windows
randygiles
| Posted in Energy Efficiency and Durability on
When you spray foam (interior) around a window, is it best to try and not fill the area were the nailing flange hits the WRB? Wouldn’t this be true because if the window ever did leak the water would have some place to go? An example is a youtube video I saw were they fully spay foam the four corners with Pur Black – but if water gets in were will it go – it will sit on top of the pur balck – unable to escape.
So it seems to me that I should only spray foam only about half way into the rough opening – thus leaving an escape path for any water intrusion if that were to occur.
Am I thinking correctly here?
Thanks for any comments
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Replies
Randy,
Before you install your window, you need to flash your rough opening. The required flashing includes a sill pan on the rough sill. This sill pan needs to be designed to drain to the exterior.
When windows leak, the water accumulates at the two lower corners of the window, on the rough sill. So that's why is it essential that there be a path for drainage at the rough sill.
The purpose of the canned spray foam is to provide an air barrier. Canned spray foam works, but not quite as well as a good European tape. Either approach can work.
It's OK to fill the space around the window at the jambs and head with canned spray foam, but at the rough sill you need to be careful. That's where you need a light touch with your spray foam can, so that you don't block the drainage path.
Needless to say, you should never install caulk under the window flange at the bottom of the window. The other three flanges can be caulked.