Basement Insulation (I can't use XPS)

AllGoNoShow

Hi there,

I live in upstate NY and have a unique basement insulation. I am going to be finishing the basement. I have read the building science websites about the best way is to use XPS against the foundation wall then build your framed wall in front, but I have had to have the foundation repaired from a local foundation company (the wall had a horizontal crack from some grading/water issues from a terrible gutter design that has since been addressed).

Well the foundation repaired consisted of a number of carbon fiber strips and wall anchors. Not only to these make attaching XPS to the wall extremely difficult, I do not want to cover the wall up because I am certain when I sell my house in the future the buyer is going to want to inspect the repair and ensure the foundation is in good repair (due to the design I can put a couple access panels in the closets to see the foundation wall).

I have an interior weeping system which consists of a one inch gap between the basement wall and floor slab and the previous owners had someone drill weeping holes through the bottom of the basement cement block to direct any water into the weeping tile (since fixing the gutters I have never seen a drop of water in the basement). I have drylocked the wall.

What is the best way to insulate without using XPS? I have seen using poly is now frowned upon. Should I use paper faced fiberglass or something like an unfaced Roxul? Would it be worth putting just a small piece of (say 2 foot) XPS along the wall on the bottom to prevent any moisture from the holes that were drilled in the block from escaping? I appreciate any help!

Windows on Wash

You can still use XPS but putting it tight to the wall is largely infeasible.

If you are stick framing it, Roxul or high density batts and standard construction with air tight drywall details is okay.

Make sure you seal up all the band joists and insulate them prior to closing up the wall.

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AllGoNoShow

So roxul over faced fiberglass? Then drywall directly over, no vapor barriers? Done! I do plan on building a 2x4 wall out about an inch from the concrete wall (I've read about how not to leave this gap but I have to because the slab has a 1 inch gap/trough in it for the interior weeping system.

As far as getting the drywall air tight, I figure you are talking about some type of adhesive applied on the studs...what kind do you recommend? Thanks.

Nick

AllGoNoShow

I came to a conclusion today I can actually get it done using XPS against the conrete wall I just have to get creative.

Does the fact I have an interior weeping/sump system affect anything with these design? Or do I just put the XPS all the way to the slab like normal? I was considering leaving a small space in case water ever gets behind the wall (basement floods or something) it can get into the drain tile. What do you think?

Windows on Wash

Make sure you don't glue it horizontally where you could interrupt the ability to weep down to the internal drain.

Best bet would probably be to rip strips of the foam as stand offs from the wall and install it that way but as long as you don't block the drainage, you are fine.

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AllGoNoShow

The gap for the weeping tile is right at 1 inch so the 2 inch foam won't go in the gap. The previous owner had relief holes drilled every few blocks as low as they could get them on the wall so that any water in the cement block will drain out there and go into the weeping tile.

I think I am going to just have to back cut the bottom of the foam board so as to not block those relief holes, but should I install the foam directly against the slab floor or just I leave say a half an inch in case I ever get water in the basement (not from outside but from an internal failure like a plumbing line bursts) it can find its way into the weeping tile. Or is having the foam board installed and sealed on all the wall, tight to the floor, a big element in the proper design/insulation.

AllGoNoShow

Well I started putting up the 2" DOW blue board, one question...do I Tyvek tape the seam where the XPS meets the cement floor (I installed it tight to the floor but I dunno if I should tape it too)?

Windows on Wash

Sealant/caulk will work better. Tyvek tape won't stick to concrete.

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