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Can you install foam insulation boards after framing a basement?

thegiz | Posted in General Questions on

Hi hope everyone is doing well. I have been driving myself crazy with trying to figure out how I’m going to insulate and frame my basement walls. I have some pex plumbing and electrical attached directly to 2 of my concrete foundation walls.  I want to hire an electrician and plumber to rewire basement and place pex through a framed wall I’m going to build in front of the foundation wall. Problem right now is that in order to get insulation board attached directly to wall I would have to remove all the wiring and plumbing. Is it possible to frame walls, have the electrician and plumber do their work and then slide the insulation boards behind the framing? Or do I have to move plumbing and wiring, then have them come back and do it again when I finish framing?


  1. Expert Member
    BILL WICHERS | | #1

    Yes, it's possible to do this, but it's a lot more work than putting up the foam first, before framing the wall. You will need to have a sufficiently large gap between the studs and the foundation wall for the foam to fit too, and you need a bit more than just the width of the foam to make sure you can slide it in (don't leave a 2" gap for 2" foam, for example, the gap needs to be a little bigger than the foam).

    What you might be able to do is to remove one or two studs and slide several layers of 1/2" XPS behind the remaining studs. The reason for XPS in this case is that you need something both durable and flexible enough that it can be bent into a bit of a curve as it's sliding in. Polyiso is probably too stiff for this, and most EPS is too brittle. You still have the issue of needing a gap behind the studs though for the insulation to fit into.

    It sounds like your main concern is that you have some existing plumbing and electrical runs strapped directly to the wall, and you need those removed prior to framing the new wall. What I would do is to arrange for the plumber and electrician to come out, remove the existing plumbing and electrical, then insulate the foundation wall in the usual way, frame the wall next, then have the plumber and electrician return to replumb and rewire the space. If those services are required to be functional while you're working, have the plumber and electrician temp things in after removing the existing runs so that you maintain service but don't have things in your way. This is really the best option, and will be less overall work for you in the long run and will also allow you to do a better job with the insulating work.


  2. Expert Member
    Akos | | #2

    If your plumbing is pex, one option would be to remove all clamps holidng the wire and piping from the wall, install the foam behind than notch the back of the studs where the wires and pipes need to go and install them that way. The studs you are putting in are non-load bearing, you can cut them a fair bit and still have no problems holding up drywall. After the studs are up have the electrician come out and staple all the wires and mount the device boxes.

    This would be a bit more work on your end but avoids having trades out twice.

  3. Expert Member
    NICK KEENAN | | #3

    I'd be inclined to go the route Akos recommends, and I'm not sure I'd even have the trades out to re-attach everything, I guess it depends on the circumstances.

    A trick that sometimes works if the plumbing and wiring is attached to the wall with concrete screws: Take the screws out and put a longer screw in the hole. Push the wire or pipe out of the way and push a piece of foam over the screw. Then unscrew the screw and reattach the pipe or wire through the hole you just made in the foam.

    If things are attached to a piece of board which is attached to the wall, I'd leave the board and notch the foam over it, then re-attach everything with screws through the foam into the board.

    The one thing you don't want to do is insulate over a water pipe, especially if you live where it gets cold. The pipe can freeze if it's outside the insulated part of the house.

  4. thegiz | | #4

    Thanks for all the advice. Easiest solution would be to have trades come twice but if I can avoid that, it would be cheaper. My electrical is so old I can’t reuse it. Added a picture just to show you where I’m at. It is mostly pex tubing with one copper connection. I also have my main water line and shut off coming out of the wall. Water lines are shoved behind a drain pipe. I could cut all the lines, use some temporary shark bite push to connect so I can move everything out front (never did this, I’m assuming this is easy and would leave temp until plumber could use better connections). Any opinion on if these connections could be left, I heard hit or miss for durability. There is a gap behind drain pipe and wall so I could slide 1/2 inch foam board behind it after I move water lines.

  5. Expert Member
    NICK KEENAN | | #5

    In a renovation it's really, really normal to frame around the existing work rather than move it.

    What you're talking about with the sharkbite would work. They are very easy to use. Three tips: use a proper cutter (copper tubing cutter for the copper, pex cutter for the pex) so you have a nice clean cut, the connectors work better with a clean cut. In order for the sharkbite to go on there has to be an open valve somewhere in the pipe so pressure doesn't build up. On copper, make sure the outside of the pipe is shiny clean, use emery cloth.

    If it's just the one outlet box I wouldn't bother with an electrician to disconnect it. Turn off the power, open the box, it's probably held to the wall with a screw. Unscrew the screw, then screw it to the ceiling to get it out of the way until you're ready to have the electrician come and make it right.

    I would say your biggest issue is going to be those drain pipes. I think you're going to end up attaching the studs to the wall to frame around them. The clean-out is going to have to remain accessible through a panel.

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