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How important is basement ceiling insulation?

Hammer 🔨 | Posted in General Questions on

So I plan on insulating my basement walls.  I also plan to insulate and carpet the floor but I wanted to paint my exposed ceiling and not finish it.  Will it just be freezing when I try to heat the basement because warm air rises?  Will you hear every footstep or hear every sound coming from the basement?  On the first floor I have laminate flooring so I’m thinking that will give some insulation.  I mean can I put foam board and attach it to bottom of first floor in between joists and paint that?  Is there a cheap alternative to somewhat insulate it but not completely finish it?  Basically in terms of heat loss how important is insulating a ceiling compared to floors and walls?

Joe

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Replies

  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Joe.

    There is no need to insulate the basement ceiling in your situation. Focus on doing a good job insulating the floor and walls (particularly good at the rim joist).

  2. Expert Member
    Dana Dorsett | | #2

    >" Will it just be freezing when I try to heat the basement because warm air rises?"

    No- it'll be fine- the uninsulated ceiling above behaves a bit like a radiant-ceiling. Unless you have a lot of air leakage or basement windows, with insulated walls & floor the basement temp will probably stay above 60F even without actively heating it, higher if you have standby losses of ducts/pipes/ water heater down there.

    >" Will you hear every footstep or hear every sound coming from the basement?"

    With a carpeted basement floor the footsteps in the basement would be inaudible from the first floor.

    >"On the first floor I have laminate flooring so I’m thinking that will give some insulation."

    From the basement you'll be able to hear footsteps on the first floor through laminate floor on 3/4" subfloor, unless there was some dampening layer. But unless you're having a dozen 200lbs Czechs dancing a polka or somebody practicing in their tap shoes, it'll be fine.

    >" I mean can I put foam board and attach it to bottom of first floor in between joists and paint that?"

    Only if the foam is a fire-rated polyiso. Everything else would need a code compliant thermal barrier against ignition.

    >"Is there a cheap alternative to somewhat insulate it but not completely finish it? Basically in terms of heat loss how important is insulating a ceiling compared to floors and walls?"

    In terms of heat loss it's NOT AT ALL important to insulate the ceiling, since the ceiling layer is between two insulated conditioned spaces. Is it important to insulate the partition walls between rooms on the same floor? Same thing. The temperature differences between adjacent rooms, or between an insulated basement and the first floor is always small compared to the indoors to outdoors temperature differences, even if one of the spaces isn't being fully heated.

    1. Hammer 🔨 | | #4

      Dana,
      So you mentioned the difference between outdoor to indoor temperatures being greater. Now if my foundation concrete walls connect and form dividers between interior rooms. Basically I have concrete walls that are interior walls. Will I have to insulate those walls as I would exterior concrete walls? The concrete is basically continuous from exterior wall.

      Joe

      1. Expert Member
        Dana Dorsett | | #5

        The thermally bridging concrete partition wall is break in the insulation, but it's not a lot of total exterior area. All total an intersecting a partition wall that Tees into an insulated exterior foundation walls adds up to about the same heat loss as a 5-8 square foot U0.5 basement window. You can wrap the partition wall in an inch of insulation if you like, but it's not really "necessary" unless you have an unusually stringent energy use target or something.

  3. Hammer 🔨 | | #3

    Thanks Brian, my rim joists and beams sit on concrete. Do I insulate the top of foundation wall with foam board as well?

    1. Expert Member
      Dana Dorsett | | #6

      >"Thanks Brian, my rim joists and beams sit on concrete. Do I insulate the top of foundation wall with foam board as well?"

      Yes- both the top of the foundation, the foundation sill, and the band joist all need to be AIR SEALED and insulated. Only foam board insulation should be in direct contact with the concrete, but in not-too-cold climates insulating the band joist and the top of the foundation sill can be insulated with high density batts:

      https://s3.amazonaws.com/finehomebuilding.s3.tauntoncloud.com/app/uploads/2016/04/09112254/021236092-insulation-main.jpg

  4. Expert Member
    Zephyr7 | | #7

    If you’re making something in the basement like a playroom or theater, and you really want to keep things quiet on the upper levels, a 5/8” drywall ceiling in the basement will help a lot. If you need more sound isolation, hang the drywall on resilient channel (make sure to use resilient channel rated for ceilings). A double layer of 5/8” drywall will help even more.

    Thermal insulation isn’t needed at all in the ceiling of the basement if you are insulating the walls and floor of the basement.

    Bill

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