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Update on XPS Installation

Posted by the-tech-guy (My Page) on
Wed, Oct 12, 11 at 8:22

I read the countless XPS questions throughout this forum but was just wondering what the best/latest way of installing XPS on the concrete walls. I have 7.5 ft poured concrete walls and bought 1" XPS T&G foam board for them. I read to buy PL-300 for adhesives but thought that would be enough. After reading many posts, they say also to use fasteners/anchors/1x3s. Is this necessary? Also after watching Holmes on Holmes install XPS they seem to overkill it. Do I need to spray foam the whole perimeter of the XPS and then tuck tape it also? Does the XPS have to be lifted off the ground when installed? How much glue is needed on the back of the XPS? Do they sell PL-300 in gallons instead of buying the individual containers? Thats alot of XPS talk here. I appreciate any advice.

Follow-Up Postings:

RE: Update on XPS Installation

I have found adhesive useless on poured walls. The leakage at the forming joints creates ridges so the foam boards don't sit flat.

There are several alternative ways you can adhere the boards to a poured wall: you can use fender washers and concrete screws on each board or at the edges to catch two boards; or use 1x1" or 2" furring strips to run across a number of boards at once; and there is one brand of XPS that has indents on each board for dimensional lumber, which can later be used to support a finished surface.

If you use tongue and groove (aka shiplap) foam boards, the tape isn't necessary. But spray foam at the bottom is an effective finishing touch to conserve energy and prevent condensation on the concrete foundation walls. If you can find them--usually only from a commercial supplier--4'x4' sheets of foam board can save effort on long walls.

Depending on your climate, your electrical needs and local regulations, in addition to the foam board, you may want to add a traditional stud wall to the interior with batts in the bays. And don't forget the rim joist area. It can be packed with foam boards or sprayed with closed or open cell foam.

Here is a link that might be useful: Basement Insulation Systems

RE: Update on XPS Installation

So many of us would be clueless without your support- thanks again Worthy!

I have a few follow up questions:

When you say to spray foam the bottom, should I install the foam board a 1/2" off the ground and then spray underneath or do you just spray the outer edge and have the board sit on the cement?

Also I use Great Stuff that comes in many different variations - Should I use low expansion foam for this job?

Is the tuck tape needed at all if I have t&g boards?

Should I put down a little of the adhesive or do I not need it at all if I use the screws or strips?


RE: Update on XPS Installation

I've only sprayed at the bottom where irregular walls and floors prevent the foam from sitting tight to the wall. Low expansion foam is useful where excess application can push window frames and the like out of plumb; there's nothing delicate to harm here. Again, building tape isn't needed where you have shiplap/tongue and groove boards. Without a helper, I've found it easier to brace the sheets with a some 2x4s and a concrete block.

(You're welcome.)

RE: Update on XPS Installation

I just have one more question before I can stop bothering you ( until framing :) ). So you are saying if I go with the concrete screws I can just return all of the PL-300 I just bought or should I still put dabs on the back?

FYI: I come from the IT field and have little knowledge about this stuff but with this forum things have been going quite well. On a sad note I was planning to build my basement with my father who is like you but he has stage 4 gallbladder cancer.

thanks again

RE: Update on XPS Installation

So you are saying if I go with the concrete screws I can just return all of the PL-300 I just bought


(Sorry about your Dad. I'm a 42-month survivor of another form.)

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