I am in the planning phase trying to decide the cost of finishing a basement. I'm trying to visualize what needs to be built and how.
My problem is that the basement has a 3" pvc sewer/drain pipe running around the perimeter on a slight decline. On the longest wall, the pipe drops maybe 2' vertical over 30' horizontal, with some vertical drains from upper floors meeting in a a few places.
I'm trying to determine how to frame this wall. If I build a 2x4 partition wall in front of the pipes (leaving access for cleanouts), I end up with a good 3-4" airgap between the back of the new wall and the foundation. Is that going to lead to problems? The basement is dry with very low humidity 3 years after construction, and there are french drains & a sump pump as well. I was going to seal the cement and then glue foam insulation to the exterior walls, but perhaps I should seal the wall and put 7" (gap + stud) of fiberglass in there instead? Or do I frame directly against the wall and build out a box around the pipe (which would look odd when finished)?
I helped my neighbor (a builder) frame his basement, and had the same exact situation. He framed the outside wall 6-8" inches out from the foundation wall (leaving soil pipe behind it, and access to cleanouts).
He then insulated it with normal batt insulation with a moisture barrier to the inside living space. (normal in this part of the country. check how they do it where you live) He did nothing to insulate the outside foundation wall, because he said you could actually "trap" moisture between the 2 walls, causing problems down the road.
I found your post and I am wondering what did you end up doing? I have a similar pipe and am trying to figure out what to do.
Quick answer: I framed in front of the pipe and left an air gap.
The pipe was 4" PVC and mounted to the wall with metal straps. I ended up building a partition wall in front of the pipe, with the back edge of the 2x4's against the pipe. I was thinking about building a horizontal box around the pipe, but then I thought about the effort required and the benefit to be gained. Building the wall in front of the pipe puts the drywall 7" from the concrete, and the loss is 4" around the perimeter of the room. To look at it the other way, it takes a lot of framing effort to box around the pipe, and you only gain 4". I'm not a pro, so the chances of me getting that box straight, level, and plumb all the way around the room were slim.
One note if you take this approach - when installing insulation, you'll have a problem getting the roll to stay between the 2x4s because of the air-gap behind. I ended up stapling some cheap deer net to the back size to keep everything in place.
The good news is that this approach makes running electric is very easy.
Also, I had three clean-outs in the sewer pipe. For each, I framed a 10"x10" box around the access cap (like framing a small window). I then marked the drywall where the cleanouts are. This way, if I ever need to use the clean outs, I have a nice framed box to secure the replacement drywall patch. I thought about building access panels for them, but why ruin a clean wall? I've never had to use them. And if I do, then I'll worry about patching it then.
Hope this helps.
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