The Secret to (Warm) Success: Insulating behind new Basement Walls

I did part of this insulation work a couple of weeks ago – to make step one before framing the walls for the new bathroom – and the rest is still on my agenda.  I’ll be insulating the south and east walls next.  First off, remember this:

Part of the reason I decided to entirely tear out the existing “finished basement” was aesthetic: it was incredibly dated with an unpleasant drop ceiling and an unfortunate layout.  I could have kept some parts of it however, if it hadn’t been totally un-insulated.  That fact made it worth while to rip off all the wall materials, 2×2 furring, tar paper  etc and bring it back to bare unfinished basement.  I can do SO MUCH BETTER than that.

From there I’ve been taking steps to warm it up before I dress it up.

  • My DRIcore subfloor tiles will give a small insulation improvement (R-4) and also just keep feet up off the hard, cold concrete.
  • The walls will get a double system – continuous 1″ closed cell rigid insulation applied directly to the concrete walls  and then batt insulation installed in the 2×4 furring walls.  That system will keep warm interior air away from the basement walls – preventing condensation –  maximize air flow behind the wall in the 1″ air gap – preventing secret mold – and also avoid thermal bridging through from the outside to interior spaces.  It also provides a normal framed wall to mount electrical outlet and switch boxes within.
  • The rim joist will get 4″ of rigid insulation (so that more is separating the inside of the house from the outside of the house on a below freezing winter night than a simple piece of 2×10 and some wood siding.

All those connections between one piece of rigid insulation and another have to be air sealed too.  I’m using cans of Great Stuff window and door spray sealant.  I don’t love the disposable cans but its in service of a much less energy wasteful future for the house.

In general the process is REALLY FUN and satisfying, although its decidedly slow to custom fit the right sized foam blocks into all odd sized joist openings and other areas of this basement.

Here’s the wall system insulated in total.

And here’s some of the process, with the 1″ rigid adhered against the walls:

Here I’ve been filling in the pockets of space between each joist in with a double layer of 2″ rigid insulation, and capping off the rest of the top of the concrete exterior wall with a sealed block of 2″ rigid:

And here’s the area of the new bathroom completely set on insulation (note: this pic was taken before the recent plumbing work.

Next step, framing up those walls.

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