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Insulating a fully below-grade cellar with an uneven rubble foundation wall

Fi7df8CZ9x | Posted in GBA Pro Help on

Hi all!

I’ve read almost every article AND every comment/question & answer on this topic but haven’t yet seen anyone with this exact dilemma so I really hope you all can help advise: (You guys have been GREAT so far)

We are wanting to insulate the walls in our fully below grade cellar (with a poured-concrete floor and an uneven RUBBLE foundation wall.

While I fully appreciate the strategy of 2″ FoamBoard glued to the foundation wall, then a pressure-treated Bottom Plate (perhaps with some “sill-seal” tape on the bottom to avoid direct contact with the concrete floor), Framing (we’d use metal studs to avoid the risk of mold), batt insulation, polyethylene vapor barrier, and lastly finishing up with a dense-armor wall board.

BUT we live in a 140 year old town house (Northeast Tri-State area) built with a fully below-grade RUBBLE foundation wall. (Cellar height: approx 8 feet. Floor is poured concrete.) Since the foundation wall is made of large uneven rocks, boulders & mortar that protrude out at irregular intervals and depths, we have no flat, even surface and so are unable to glue up the 2″ foamboard.

Since this is the first step in the process, we got a prob’m, as they say…

How do you guys recommend that we insulate OUR unique situation?

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Replies

  1. jklingel | | #1

    A vapor barrier in a basement? I'm not a pro, but were it mine I'd take care of any exterior water issues, frame it w/ wood (treated bottom plate), use rock wool insulation, NO vapor barrier, and air seal. The space between the framing and the rubble foundation will lead to convective loops and some heat loss, I believe, but I'll let someone else comment on what to do there. Spray foam? buildingscience.com may have some info, too.

  2. GBA Editor
    Martin Holladay | | #2

    Michael,
    There's only one way to insulate basements like yours: closed-cell spray polyurethane foam. Call up a spray foam contractor; they are very familiar with this type of foundation and will be happy to help you.

  3. Foamer | | #3

    Michael,

    Think "closed cell spray foam". Then take a deep breath and think "closed cell spray foam" again, pick up your phone and call for help. John is right that you should deal with any water issues that you may have from the outside if that can be done, but as far as the inside work goes spray foam is your answer. Spray foam is what I do for a living and I am absolutely biased so for an independent opinion, check out these articles at buildingscience.com: Insight 045 - "Double Rubble Toil and Trouble" and Insight 041"Rubble Foundations".

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