Backer rods – GreenBuildingAdvisor

Most backer rods are essentially the same..

You might get higher quality from a glazing supply store compared to the local hardware store but they essentially do the same thing: stuff the gap so you can caulk on top of it.

I usually avoid it all together and just use spray foam as the backer rod. Fill the top and sides with ¾-⅞ of the depth and after it cures, use sealant to make it water and vapour tight.

You can use backer rod and sealant at the bottom, to leave space for water to gather and flow out (hopefully you’ve sloped your sill).

Or you can use spray foam as the backer rod if you’re careful enough not to fill the entirety of the gap but spray just a bit in a zig-zag pattern to keep it near the inside of the sill, which replicates a backer rod.

Hope this helps,

Jamie