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No vapour barrier between foundation wall and mudsill

TG8 | Posted in Energy Efficiency and Durability on
I’m having a detached garage/workshop built in Ontario, Canada (Zone 6; in USDA terms Zone 5, as far as I can tell). 

After resolving the insulation issues around the concrete slab (, I have another issue I need some advice on.

The framers did not put any vapour barrier between the top of the foundation wall and the mudsill (2×6). I don’t know why. They did put BG73 from Conservation Technology (, which is 4″ wide, as an air barrier, which I asked for, so I supposed there’s partial protection there. Also, it seems like using PT wood for the mudsill isn’t a code requirement so it was not used. So I have two questions:

1. I was planning on using batt insulation and vapour barrier as insulation in the walls, but now I’m wondering if dampness in the mudsill will bring moisture into the wall cavity behind my vapour barrier. Should I use spray foam insulation instead? What other near term issues should I be concerned about?

2. What are the long terms implications and what can I do to mitigate any future damage? 

The building passed structural inspection from the city, so I’m not sure if he didn’t notice it, or it’s not a code requirement to have vapour barrier there. 

I’ve attached a photo of the workshop to show that the rear foundation is 2 feet higher than the front.

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  1. Jon_R | | #1

    My guess is that the EPDM gasket will provide enough separation/isolation to keep the wood and cavity dry. I don't think it is needed, but you could inject some sealant to fill the gap caused by using a 4" wide gasket with 2x6s.

    Do test your air sealing.

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