Insulate on top of Rolled Blanket insulation in the basement ?

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Posted by: from Hamilton
3/23/2020 at 9:59:46 PM

I live in Hamilton Ontario, my Semi-detached is 7 years old. My basement is insulated with an R12 Insulation blanket over almost the entire wall, there is only 7 inches left at the bottom.

My question is, can I insulate over what's there?

My concern is the vapor barrier.

What I find strange is that my neighbor did his basement and the city inspector told him it was OK to put Roxul on top of the Blanket insulation without dealing with the vapor barrior. I don't think that is right.

I was thinking of scoring the existing vapor barrier as much as I can, insulate on top, and re add a vapor barrier on top of my framed walls.

I tried my best to search online but there are no real answer to be found, or non for our climate.

If that makes any difference, I have almost no exposed foundation on the outside. First , I have 3 walls only (it's a semi), and the side and the backyard have a cement pad/sidewalk that goes almost all the way up to the brick, I would say maybe 6 inches exposed.

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Date/Time3/23/2020 at 11:23:41 PM

The vapor barrier is to keep condensation out of the insulation.

Roxul can be added on top, but it must have another vapor barrier.

Removing the exiting vapor barrier prior to adding the Roxul will do nothing.

Just insulate over top, apply new vapor barrier.

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Date/Time3/23/2020 at 11:32:16 PM

Hi Stephen. I have run into this several times in my 30 years especially the last 10 since they're rapping basement instead of framing them. You need to remove the existing 6 mil Vapor Barrier and much as possible if not cut openings in it everywhere and anywhere then leave the insulation and put your framing in front of it one in away from any concrete wall is minimum for air Space by code. Once you've done all your framing you can insulate all the walls with R12 and then install 6 mil vapour barrier over the two by four walls always keep Vapor Barrier on the warm side of drywall. If you did not remove or at least cut open the existing Vapor Barrier you would have major condensation and mold issues.

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Date/Time3/24/2020 at 1:50:50 PM

Your suggestion sounds practical.



Partex Design Build Ltd.

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Date/Time3/27/2020 at 2:37:10 PM

In my opinion the inspector gave incorrect advice if this is true. The Code requires vapor barriers to be on the warm side of the insulation in Canada. There is also a rule of thumb that allows it to be placed partially within the insulated wall provided there is no likelihood of condensation occurring (if the dew point occurs beyond the vapor barrier). You can find information on this online if you Google dew point in walls; calculations involve use of the psychrometric chart (it depends on humidity). In Alberta insulation is permitted to be placed in contact with a concrete wall however it's a good idea to leave a little space for drying. Current Energy Code requirements are R-20 for basement walls however there's an exemption for existing homes. Recommend spacing studs at 24" o/c to minimize thermal bridging and also recommend Roxul insulation which has a higher R-vale.

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