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rickcet 10-13-2011 08:28 AM

Putting Up XPS On Basement Walls
I am in the phase of putting up 1" XPS on my poured concrete basement walls but not sure on what way to do this. Do I just use adhesive such as PL-300 or do I use just concrete screws or do I use a combo of screws and furring strips? Since the board is tongue and groove do I still need to tape the seams with Tuck/Tyvek tape? Do I need to spray foam the top and bottom still?

leungw 10-13-2011 10:57 AM

Glue alone is fine. If the wall is not perfectly flat, you can use something heavy to temporarily hold the xps in place until the glue dries (about a day). I used 2x4 and plywood.

I used 2" XPS and found that the tongue and groove do not line up most of the time. For those I ended up cutting the tongues and taping the seams. I did not tape the ones that fit well.

I put spray foam at the top and bottom to seal the gaps, after I put 2x4 frames about 0.5" in front of the xps.

If you plan to finish the basement, check with your town to see if you need fire blocks. If yes, I would suggest to put fire blocks at the top first before doing xps.

rickcet 10-13-2011 11:23 AM

Thanks for the reply. I have one other question: How much glue should go on the board? Assuming its a pretty smooth wall do you just dab a little in each corner and then the center or do you do long verticals layers? Also is buying the tubes of PL-300 at HD the way to go or is there better/cheaper route?

leungw 10-13-2011 11:42 AM

I had the same question on glue pattern when I did this. I looked on different forums but didn't find a definitive answer. I might have over-done it but it worked. I did two "S" on each 2x8 panel. If your walls are in good shape, I think you can get by with less. I was able to do about 4 panels for each 10oz PL-300 tube.

I bought the PL-300 from HD. I found some online sites that sell them either in bulk or in 28oz tubes, but after shipping they came out to about the same price.

rickcet 10-14-2011 08:41 AM

I am getting people from other sites saying concrete screws are the only way. Did you have any trouble at all glueing these boards to the walls? Any tips? Is your basement now finished?

leungw 10-14-2011 08:52 AM

No, no issue with mine. I did exactly what was posted before. Just make sure that the xps is touching the wall. If not, lean something heavy on it and allow the glue to dry for at least a day.

If screw is the only way to go, I would be reluctant to do xps because of the number of holes needed in the walls.

Basement is about 80% done.

leungw 10-14-2011 09:02 AM

2 Attachment(s)
Some old pictures.

rickcet 10-14-2011 09:23 AM

Looks great! Did you do the rim joists with XPS also? Is that pretreated wood for the bottom plate? Are you going to use fiberglass still?

leungw 10-14-2011 09:44 AM

Yes, I replaced all the fiberglass with xps at the rim joists, then put new fiberglass on the xps.

Yes, bottom plate is treated wood. It's required in my town. I have seen suggestions here saying that a foam sealer should be put under the bottom plate. But by the time I saw it I was already done with the bottom plates so I didn't do that.

Foam sealer (available in HD as well):

My original plan was to just leave it like that and then drywall. The inspector insisted that I fill the voids with fiberglass. He said that xps is highly combustible and requires a thermal barrier directly on top. Having drywall almost 4" away is not good enough. I didn't want to argue with him so I ended up filling all the voids with fiberglass.

rickcet 10-14-2011 09:58 AM

What part of the country are you in if I may ask? Have you been doing everything yourself- you do this for a living? What are you doing with the floor- plywood over XPS? What about heating- just opening up some returns/ducts?

leungw 10-14-2011 10:09 AM

I am in NJ. Yes, so far I am doing everything myself, and no I don't do this for a living. It has been a long project. I don't want the basement work to get in the way of my two little kids' activities. Being in IT doesn't really help either. :laughing:

For floor, I already put Delta-FL on the slab, then plywood. I plan to have someone come in to do carpet when I am done with everything else.

I don't know about heating yet. The basement is now the most comfortable place in my entire house, probably because of the XPS and fiberglass. I will most likely try an electric heater first if needed. If it's not enough, I will tap into the HVAC trunks.

rickcet 10-14-2011 10:34 AM

Why didnt you go with XPS on the floor? Is Delta-FL cheaper or better performance?

leungw 10-14-2011 11:40 AM

I have read suggestions to leave a small gap between the wood framing and the xps on the wall. Putting plywood directly on top of xps on the floor seems to go against the suggestions.

I special ordered Delta-FL at Lowes. I think it's about $160 for a roll that covers 320 sq ft. (Don't remember the exact numbers.)

Gary in WA 10-14-2011 10:02 PM

Check with your local AHJ. You may need fire-blocking every 10' lineally, against the concrete wall, not the foam board, as per code requirements.
The foam board may need to be positively attached (fasteners) to meet code, though local may accept wall touching foam.

The glue should stop any air movement behind the foam, no air gaps between insulation types- batt to foam;

The sill sealer is important if you have an older slab without plastic sheeting underneath to stop moisture wicking from the earth, through the p.t. plate, to your studs;

It also stops air getting to the air-permeable fiberglass insulation via under the plate to cause convective loops. You'll want to air seal the drywall- ADA;

It stops your warm wall from acting as a "heat sink" to the cold slab/earth below, saving energy.

leungw 10-18-2011 12:48 PM

1 Attachment(s)
I just saw GBR's comment and can't agree more. Make sure to check with your town to see if you need vertical fire block as well. It will be a pain to add later. The idea is to completely block off the wall cavities every 10ft.

This is what I did. If you look at the first picture I posted earlier, you will see a piece of wood stuck vertically between two pieces of xps. It has to go all the way to the concrete wall. Notch both the top and bottom just enough to install top/bottom plates. Then line up a stud in your wall framing to meet the one that's touching the concrete.

I used treated wood since it's touching concrete. Some had twisted a bit by the time I started framing. I used Great Stuff Fireblock to fill the small gaps.

Quick sketch of top view with Paint....

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