What is the best way to do a cottage reno adding an insulation blanket?

Depending on how much insulation you add, and the type, you could leave the exterior walls intact, but I wouldn’t do that with just 2 inches of rigid foam insulation. 2 inches of EPS rigid foam would be a vapor barrier, but it’s not thick enough to protect your wall properly.

Have you ever heard of the 2/3rds rule? That refers to keeping at least 2/3rds of your insulation outside of your vapor barrier, so given that it’s a 2x4 stud wall with fiberglass you are looking at about R15 at best. And 2 inches of foam will be between R8 and R10, so the interior surface of foam would be cold and at risk of developing condensation. Here is our building science video that explains it best –

Building science made easy – video

So my two cents would be – yes on theWRB weather barrier membrane on sheathingas you will then be airtight, and if you add 6 inches of rigid foam insulation you would have R24 and a warmer ‘vapor barrier’ surface of the interior foam. That would be a super insulated, airtight and durable wall. It may be more than you planned, but this way you save all the labor and cost of removing sheathing and insulation.

Alternatively – you could do the same thing (leave the sheathing and add a WRB) then add 2 inches ofrigid mineral wool / Rockwool insulation因为它不会留住水分。这是一种更安全的方式。在这方面，矿棉是一种“万无一失”的绝缘材料，因为水分会穿过它，不会造成伤害。2 inches of Rockwool you could attach with strapping, and if you wanted to go the thicker foam route then |I’d look atThermalwall exterior wall foam insulation panels. They are easy to attach, are perfect for insulation as well as vapor protection.

And you canread here to find out how to choose the right rigid foam insulation用对了，墙壁就会变干。

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