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311Hemi

Basement walls

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Starting to plan the next move for after the egress window is installed (going in in the next week or two). Currently thinking I will be using large sheets of rigid foam and possibly Z-channel, but some stuff I am read says the rigid insulation should be continuous, and then the framing is put on over that. A vapor semi-permeable rigid foam is recommended to allow inward drying. This is installed against the block wall from floor to the top of the wall, on top of the block wall, and up the rim joice. No interior vapor barrier is recommended, the exterior one is semi permeable (or impermeable) as I have mentioned. One just allows more inward drying from what I understand.

My basement has walls that I believe were painted with a sealant, I have never seen them leak. Drain tile was installed right before I bough the house (on the inside) and I have never seen water in the basement. I do have to empty my dehumidifier that's down there every week.

Anyone have any thoughts on this? The info I am reading is from buildingscience.com.

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Hi Hemi

I was on the same webiste and plan on doing the same thing to my basement very soon. Lets hope we are doing it right.

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FWIW - I had place built last year, with unfinished basement, and I trust the contractor. He put thermax (thermex?) 1" foil backed foam sheets, and EVERYTHING/SEAM was taped. Just like you said you read.

He told me when I frame, just put up studs inside of it, and do nothing else, no barrier, no insulation, just leave it like that - stud it and rock it and that is best. I did spray foam insulate the side plates (terminology?) above the block and framed walls of the basement. It is nice and tight, and no water issues, though we did make sure the drainage was well taken care of, and it is in sand area.

I did have some pics that I think I posted some time ago here. I can always repost them if you are interested.

Good luck!

edit - Found them, sorry for the size of them...

IMG_9027.JPG

IMG_9032.JPG

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Thanks BoxMN, that is kind of what I had in mind. I plan on use the 2 inch thick pink rigid foam, then use fir strips that screw into the block to suppor the sheetrock. Then probably overkill it and possibly do more 1/2 inch foam or the foil backed foam inbetween the fir strips. I am going to do a little more research before I move ahead.

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When building a new home, the contractor used foil faced thermax due to it having a fire rating. I believe state building code requires on new construction something fire-rated to be placed on the inside of foundation walls if they are going to be left unfinished. thermax when taped at the seams also counts as a vapor barrier, so an additional vapor barrier will be a waste.

if the basement is stud wall and batt insulation, and will be left unfinished then a fire-retardant poly is required. If its finished then the sheetrock counts as your fire-rated material, and a vapor barrier will be required behind it.

so if you foam it, then stud over the top i would put a poly for vapor barrier, if you use thermax and tape the seams, then you shouldnt need an additional vapor barrier.

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When building a new home, the contractor used foil faced thermax due to it having a fire rating. I believe state building code requires on new construction something fire-rated to be placed on the inside of foundation walls if they are going to be left unfinished. thermax when taped at the seams also counts as a vapor barrier, so an additional vapor barrier will be a waste.

if the basement is stud wall and batt insulation, and will be left unfinished then a fire-retardant poly is required. If its finished then the sheetrock counts as your fire-rated material, and a vapor barrier will be required behind it.

so if you foam it, then stud over the top i would put a poly for vapor barrier, if you use thermax and tape the seams, then you shouldnt need an additional vapor barrier.

What do you think about the info provided on the HSOforum I posted? Many things I have read pointed to this being a great source of info for when finishing a basement.

Are you saying putting a poly vapor barrier on the inside side of the wall, between sheetrock and studs? Wouldn't that allow moisture on the entire backside of it and not allow that moisture to dry out at all and form mold?

The link I provided says that the best insulation to use is a foam insulation that allows the foundation wall assembly to dry inwards. They recommend a foam that is vapor semi-impermeable or semi-permeable. Would the foil covered foam fit into one of these categories?

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i was just going by what was required by local building code at the time. what is required varies from location to location

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The best and suggested way to finish off your foundation walls is use drylock paint on the block for your moisture barrier, then use a closed foam insulation blue or pink(XPS) tape all your seams and then frame your stud wall in front of that. I would never frame or attach framing to the block wall and then fit in your insulation...you loose a inch and half of insulating properties behind framing members. Also you DO NOT need to install poly for use as a vapor barrier over the foam.

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The best and suggested way to finish off your foundation walls is use drylock paint on the block for your moisture barrier, then use a closed foam insulation blue or pink(XPS) tape all your seams and then frame your stud wall in front of that. I would never frame or attach framing to the block wall and then fit in your insulation...you loose a inch and half of insulating properties behind framing members. Also you DO NOT need to install poly for use as a vapor barrier over the foam.

Thanks for the info...this is what I am currently planning on!

Do you glue the XPS to the walls, or use a Hilti and some sort of fasteners right into the block wall?

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Use PL 300 for foam applications...it's about $1.29 per tube, DO NOT use PL 400 or other glues because you will burn/melt the foam....good luck

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Check with the building officials where you live and see what they expect. My bother in Lino did his earlier this summer and they had a sheet they gave out that indicated what they wanted. I am pretty sure that I learned that each city may have different requirements.

My research led me to think that the sprayed foam was the best solution over all but it got pricey.

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I priced out the spray insulation and most quotes I got were hovering around $2 a square foot while the 2 inch pink rigid foad was about .50 a square foot. I would have liked to do the spray foam but for that price its kind of a no brainer.

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