I finishing a part of my basement and I want to put rigid insulation>studs>batt insulation in stud bay>drywall.

I have a wall that has copper pipes, pvc pipes, and gas pipes flush to the concrete wall. There is also a main clean out on the floor that's about 2 inches away from the concrete wall.

I'm thinking about moving the pipes off the concrete and putting rigid insulation on the wall. Then frame my wall in front of the main clean out.

Is it okay to have an air gap of about 4in from the rigid insulation to the studs? Also is there a better way to insulate this wall because it requires moving a lot pipes. enter image description here

  • 1
    Can you provide some pictures to help us visualize the space? May 25, 2018 at 14:38
  • I'm not a plumber/gasfitter, but when I've had problems with the gas pipes in my house, I found out that there are reasons (not sure if it is typical code or just local regulations - Maryland, USA) that you typically can't permanently box in gas pipes - i.e., they can be covered up but only in a way that allows easy access, such as removable ceiling tiles or access doors. That is different from copper or other water pipes which are routinely covered up, resulting in problems if there is a leak but no danger of a potentially explosive gas buildup. May 25, 2018 at 14:44
  • I have added a picture May 25, 2018 at 14:58
  • Why are you interested in such a high level of insulation? Is this partially above grade?
    – isherwood
    May 25, 2018 at 15:37
  • 1
    I read rigid insulation is recommended for basements. This all below grade May 25, 2018 at 15:40

1 Answer 1


It's fine to have a gap between the rigid insulation and the energy wall IF you don't allow airflow to occur between the gap and your conditioned space. If there's free flow of air from on space to the other, the insulation in your energy wall effectively does nothing as you've now basically placed the insulation in the middle of the room.

This means relying on your drywall, plus something at the top of the gap, to completely block airflow. For that reason it may prove too complex.

  • Thanks for the answer. When you say energy wall? You mean exterior wall right? I want to the rigid insulation on the concrete wall the gap is between the insulation and the stud wall. I have attached a picture May 25, 2018 at 15:03
  • 1
    Energy walls are the wood-framed walls inside the foundation.
    – isherwood
    May 25, 2018 at 15:36

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