What works best under a foam exterior?
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| Posted in GBA Pro Help on
I’ve watched the videos on installing foam board on the exterior of a house but what does the foam sit on at the the sill plate? I’m leaning towards a metal drip edge but others use Azeck board.
The reason I ask is that the videos address the windows well but what about the doors. We are not planning on putting bucks at the rough openings of the doors, just the windows. Since the door frame will be hanging out over the foam I just wanted to know how to support it if I use a metal drip edge like in the videos.
I also need some advice on a bug screen, what should I use?
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Replies
John,
Under your doors you can install a solid piece of blocking (lumber) the same thickness as your foam.
To keep the insects out of your rainscreen cavities, use ordinary insect screening. Aluminum and fiberglass screening are the most common types, but you can order nylon, polyester, or bronze screening if you prefer.
Ok thanks Martin that helps me but now my contractor wants to leave out the foam board where the ledger board attaches to the house for the porch. The porch covers almost the entire one side of the house. I saw where building science attached the roof ledger board over the foam on the Habitat For Humanity Westford House video. Can I do that too with both ledgers or do I have to give up the foam board in both areas along the entire length of the house. On the inside I plan on open cell spray foam in the joist areas for first and second floors. The rest of the walls will be dense pack cellulose in Zone 5. I'm trying to learn because my builder has not done this foam board application before.
John,
There is a discussion of porch ledger and deck ledger attachment in foam-sheathed homes in the comment section on this page: How to Install Rigid Foam Sheathing.
I don't think that porch ledgers or deck ledgers should ever be attached to a building; instead, a porch or a deck should be supported on independent footings. It's not that hard.
If you insist on attaching the ledger through the foam, here is one detail (from a document published by the Cold Climate Housing Research Center, REMOTE: A Manual).
Click on the image to enlarge it.
Thanks Martin, I changed things for the porch so we don't have a ledger board and the porch sits independent from the house because I'm running the porch boards perpendicular to the house. My last question hopefully is how do I flash and vent the wall with foam insulation of a wall that runs down from a higher roof to a lower roof. The one video on foam installation shows that they run the foam board down the outside wall from the higher roof through the attic of the lower roof and ending at the top plate of the lower wall. Do I treat the venting with bug screen and metal drip cap the same as a wall at the bottom near the foundation and how do I flash the lower roof to the upper foam board wall? How do I make that all work? Thats something that hasn't been addressed in any posts or videos that I have seen. I hope the description makes sense to you and thank you for all the help.
John,
Either way will work, as long as your thermal barrier and air barrier are continuous. Hopefully, your designer can draw these details so that your builder doesn't have to make job-site decisions on the fly.