Air Sealing exterior of historic home
1869farmhouse
| Posted in General Questions on
I’ve done my fair share of air sealing – both interior and exterior. But the most recent home I’m working on has the most egregious leakage I’ve seen. In the exterior, under the soffits, there is a solid 1” gap that leads to the interior wall cavity. I’ve used spray foam to seal from the interior, but I questions it’s use outside. What would you all recommend in this situation?
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Replies
Do you have a description of the wall assembly? That could help provide a better recommendation.
It’s a typical stud wall, true 2x4 with rockwool batts and 1/2 Sheetrock on the interior. I can peer into this gap from the outside and see the top of the rockwool batts inside. I’ve just never had to seal such a large gap from outside before. Not sure how well great stuff works from the exterior and it’s way too large for caulk or even acoustic sealant.
I would expect that this was to allow the walls to dry. We now have rain screens designed to let the sheeting dry.
When retrofitting older homes, we need to be careful because we are changing the air flow through the assembly and the ability for the assembly to dry.
I’ve seen some videos on Matt Risinger where he added dimple mat (used on foundation) on the interior sheeting of the exterior wall. He created venting to get air between the sheeting and the dimple mat. The air was made to come from the basement and exit through the top plate.
In your case, you have a vent at the top of the wall on the exterior.
If you have not closed up the exterior wall, you could create a channel between the outside sheeting and the insulation. You would connect and seal the channel to the gap at the top of the wall you could cover the gap on the outside with a metal trim that has holes (vented) to let air out. You would need to figure a way to introduce air into the gap from the bottom and should be doable unless there is brick at the bottom of wall. This is the same idea as a vented cathedral roof.
If this all sounds crazy to you, then maybe cover the gap with a piece of wood or pvc trim and move on. Sometimes we don’t have any other choice because of where we are with insulation and drywall on the inside.
I think this bypass is not uncommon in balloon framing.
If you’ve got clear access to the cavity from outside, a quality tape like zip or siga might work. If not then foam is probably the best option. Maybe a larger frothpak type kit might be in order.
I dealt with this scenario in my own house when I dense packed the walls with cellulose. It was painful work stuffing fg wads in those bypasses in every cavity to keep the cellulose from filling up the soffit and piling into the attic.
A gap that large seems to call for a piece of trim. Would that work?
I’m going to use a combination of the above advice. Little foam, then a piece of trim, then some quality caulk. Hopefully it does the job, because right now the thermal cam is blowing up!
Just as an update for anyone in a similar quandary, I didn’t end up using trim. It was going to conflict with the siding, so I filled the gap with Great Stuff, then cut the excess foam flush, then applied butyl flashing tape. It ended up working really well.