Hello! I am renovating, and after removing the plaster and lathe in my kitchen I discovered that someone had poured concrete down the stud bays of all the exterior walls on the first floor. No idea why, (Misguided insulation? Racking support? DIY bulletproofing?) but it's there and I don't want to remove it in case the house has settled onto it and it is now a structural component. Also it's a few tons of rubble I'd rather not tangle with without cause.

My current plan is to create a false wall of 2x4's laid flat and screwed into the old studs to run electrical and some insulation. I'm hoping I can insulate with some foil faced EPS I have on hand to at least get some kind of R value. Anybody have any experience with this, or ever heard of it being done? I'm reluctant to lay the 2x4's longways as the kitchen is rather tight already.

pic of the concrete, the new studs are my addition https://imgur.com/a/OvLcHTt

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Wonderful_Promise_69 OP t1_jdtmtt1 wrote on March 27, 2023 at 2:26 AM

#2,382,945

The false wall is also what I'm going to use to hang drywall, shelving and cabinets.

Inshpincter_Gadget t1_jdtych4 wrote on March 27, 2023 at 4:11 AM

#2,384,567

Holy shit that's crazy bro.

Foil-faced insulation, I think, is completely vapor impermeable. If so, then you have to be ultra careful where you use it. Last thing you want to do is trap moisture inside your walls and end up with 50 tons of moldy stinky concrete wall filler.

In my climate zone vapor barriers are not really needed, so I avoid using them.

In cold zones you want the vapor barrier towards the warm in winter side of the wall, so that the steam from your hot cocoa does not condense into water droplets inside your wall.

If condesation is a concern then use the Rockwool product -- I forget the name.

Gosh, fucking concrete in the walls. Unbelievable.

Man, if you're brave enough to get rid of that shit... I wonder if closed-cell spray foam would replace some of that stiffness you are afraid of losing. (That would also be a vapor barrier, though).

If the studs are in good shape then I think the concrete isn't really doing much. There's that gap at the top of the walls. There's nothing sitting on top of the concrete, so I don't think it's really holding up anything.

I guess I'm just getting stuck on the idea of having such terrible wall insulation for the sake of keeping such a bunch of garbage inside the walls where the insulation should be.

MrMonopolysBrokeSon t1_jdv53tg wrote on March 27, 2023 at 12:58 PM

#2,390,017

Take lots of pictures, you'll (hopefully) never see that again!

Your plan seems solid to me, except you'd get better insulation value out of your eps by putting it on the wall first then adding your 2x4 furring over top. The new studs would be anchored to the old ones with long screws through the insulation.

aenorton t1_jdwbmmi wrote on March 27, 2023 at 5:48 PM

#2,396,387

Could this have been someone's attempt at making a tornado shelter?

Wonderful_Promise_69 OP t1_je2bcqx wrote on March 28, 2023 at 10:05 PM

#2,429,754

Replying to aenorton (#2,396,387)

Possibly! I'm in the northeast coastal US, so probably not?

Wonderful_Promise_69 OP t1_je2d1o5 wrote on March 28, 2023 at 10:17 PM

#2,430,034

Replying to Inshpincter_Gadget (#2,384,567)

I'm more worried about the lateral racking support as opposed to vertical loading, its old balloon framing. Spray foam and the dumpster fees are wildly outside my budget right now unfortunately. Would the foil facing inside the house create condensation between drywall and insulation? I guess it's better to get moisture in the new stuff than the structural stuff, if I had to choose. Thanks for your response!