We've been planning to renovate a large room in our basement, where there are three exterior wals. The house dates from the 1940s, and the walls are concrete blocks which were parged on the inside, and then covered with tar paper and strapped, with only thin wood panelling on top. (One wall has a brick finish which we'd like to leave alone.) Needless to say, the basement was very cold. I've removed all the panelling and strapping and paper and I've chipped away some of the parging to see what the condition of the blocks are like underneath. I had an engineer come out and there are no structural concerns with the foundation walls, so it's time to finish the basement.
What are my options in terms of finishing from the foundation wall outward? There is no obvious moisture coming in from the outside. Here are some of the ideas I had:
1. Remove remaining parging, point any loose mortar, paint with bitumen and then frame/insulate.
2. Re-parge, apply tar paper again, then frame/insulate.
3. Use some combination of spray foam and framing?
Any advice would be helpful, thanks!
If there are no moisture or structural problems, it sounds like you're ready to frame/insulate and finish! If parging is nicely done/not in the way of framing then don't go through the trouble of removing it. Spray foam insulation would be a plus.
If it were me, without a doubt I would .5 to 1 inch of space, frame, then spray foam. We have used the product multiple times. It is amazing how fast it makes that space very cozy. No moisture, no smell, bugs, just done. Run General plugs before or after spray is done, (preferably before). Highly recommended.
Hope this helps.
As others have correctly mentioned number 3 is the best option. Number 4 I would go as second best on your list.
Bitumen and tar paper are petroleum based products that are NOT intended for use in an interior of a home. Put that stuff in your home and you're filling it with VOCs.
Good luck with your project!
Hi Steve, just out of curiousity, if we went with Smartwalls, I believe insulation included wouldn't be up to code for basements. I'm told we can put a layer of XPS underneath. Would that mean that we'd have to re-parge first?
No need to re-parge. You are correct about needing more insulation. Smart walls are R16 and minimum code for basement walls is currently R20. If you use something like a rigid foam tape the seams with tuck tape. Another advantage of spray foam is spray foam also gets sprayed on the rim joists and that's a big area for heat loss. You will still have to insulate the rim joists with regular insulation methods using smart wall.
Another question -- the walls are dry now, but is it worth installing a waterproof membrane in the anticipation of potentially having moisture coming through in the future? I don't want to dig up the floor now for a perimeter drain system but I feel like this part would be easier to do in the future if the wall membrane is already in place (rather than having to rip up the walls in the future to start from scratch...)
If the walls are dry and there are no serious cracks, that's a positive. The best way to prevent water ingress is by managing water drainage outside the building. Minimizing the amount of water that gets to the concrete blocks in the first place will minimize how much water gets into the house, including evaporation from the concrete blocks themselves. Many people look at it from the point of view that as long as there is no visible water means no water is coming in, but water will evaporate from the concrete into the house. Ideally, prevent the concrete form getting wet is the best place to reduce water (in any form) from getting into the house.
Peace of mind is helpful too. If adding a membrane inside will do that, then by all means, find a product that is intended to do what you want it to do and is intended to be used internal to a house.
Spray or roll a waterproofing compound over all the exterior block and parging...then frame 2x4 walls 1" from the exterior walls...install insulation roxul best and then vapor barrier warm side of room...costs about $80/every 40 sqft. + labor...drywall then like any other reno.
If the parging is not loosening from the blocks it would seem there is no point in removing it. Interior dampproofing though not required by Code is probably a good idea as it may help reduce moisture passing through the wall - if dampproofing is applied it is required to terminate at grade level. Double check with your local municipal authority however in all likelihood you will need to insulate to minimum R-20 to meet current Energy Code requirements - possible solutions would be spray foam, 2" of rigid insulation plus R-12 - 14 batts or R-20 batts. (Smart walls probably not a good idea.) Brick wall unfortunately should be insulated as well if it is an exterior wall.
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