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Basement Insulatin 2” XPS

Posted: Sat Feb 16, 2019 12:07 am
by jackson54
Hi Shannon,
I am insulating my basement with 2” XPS, using adhesive to the poured concrete wall. My rim joist were previously sealed and insulated by the builder.

I have about 8 feet and 10 inches of concrete wall, The very top of the concrete doesn’t allow for a straight piece of xps, is it ok to XPS most of the way up the wall, (i have solid 8X4 XPS foam board then i rip smaller pieces down to 7”’s and lay them across the top) then cover the remaining 1-2”’s of concrete with spray foam? If this ain’t making sense i can send a picture.

Thanks! I appreciate all you do!

Re: Basement Insulatin 2” XPS

Posted: Sat Feb 16, 2019 7:55 am
by Shannon
That will be fine. I would seal the butt joints with spray foam.

Re: Basement Insulatin 2” XPS

Posted: Sat Feb 16, 2019 8:44 am
by jackson54
Is tape ok for the butt joints or must use foam? I used tape on the long verticle joints but can definitely re do them.

Re: Basement Insulatin 2” XPS

Posted: Sat Feb 16, 2019 4:51 pm
by Shannon
If they are lapping joints then they are fine but I would foam butt joints

Vapour barrier yes or no

Posted: Wed Feb 20, 2019 11:47 pm
by RScobs
Hi Shannon
In your basement insulating video you mentioned that putting EPS against the concrete wall provided some insulation and acted as a Vapour barrier. Why put poly on the inside of the insulation as well?


Re: Basement Insulatin 2” XPS

Posted: Thu Feb 21, 2019 10:40 am
by Shannon
No actually I said it adds insulation value and provides the moisture barrier you need against the concrete wall.
Moisture barrier and vapour barrier are two different items. Moisture barrier separates and protects the insulation and wall framing from moisture that comes through the concrete , Air/vapour barrier prevents the passage of warm moist air in the basement from passing through the wall and getting to the cold zone of the wall construction where it condensates and can start to cause mould issues with in the wall.

Re: Basement Insulatin 2” XPS

Posted: Mon Feb 25, 2019 9:42 pm
by WillLee
So let me know if I'm correct here regarding moisture and vapour barriers and rigid foam:

If I'm using 0.5", 1.0" or 1.5" rigid foam against the concrete wall, it is functioning as a moisture barrier only. Placing batts then a poly vapour barrier would be necessary here before drywalling.

If I'm using 2.0" rigid foam it is functioning as a moisture & vapour barrier. Placing batts and dryingwalling without vapour barrier would be the procedure here.

By the way Shannon, you mentionned that you now fasten the rigid foam with tapcons and roofing washers. What kind of roofing washers do you use? Do you have a picture or a link to the type that you're using?

Re: Basement Insulatin 2” XPS

Posted: Mon Feb 25, 2019 9:58 pm
by Shannon
In all cases the foam is still a moisture barrier and adds insulation value to the wall. In some areas 2” foam could also be the air vapour barrier. It’s kinda complicated.
Your local building permit office will have final say on what is allowed for your area.

Here is a similar washer : ... 42456.html