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Community and Q&A

Can a partial insulation upgrade cause problems in an old house?

tstan42 | Posted in Energy Efficiency and Durability on

We are planning to upgrade the insulation in only the renovated areas of the house, with either foam or dense-packed cellulose. Will the increased air-tightness in those areas force warm/moist interior air to seek equilibrium by moving through exterior walls that have not been upgraded, dramatically increasing the amount of air moving through the poorly-insulated walls and causing cavity condensation?


  1. GBA Editor
    Martin Holladay | | #1


  2. tstan42 | | #2

    Martin, would you mind elaborating a bit? is it really that simple???

  3. homedesign | | #3

    Good question
    Todd, you may find this discussion interesting
    in particular
    Michael Blasnik (Comment #24)
    More or less agrees with Martin's "No"

  4. GBA Editor
    Martin Holladay | | #4

    As far as I know, it's pretty simple. If you have always had condensation problems in the older part of the house, you will continue to have them.

    If the older part of your house has always been problem-free, it will probably continue to be problem-free -- until some relevant component wears out, breaks, or is damaged.

  5. Perry525 | | #5

    We are taught that hot always moves to cold and water vapor always moves to cold and or areas of low pressure.
    If you continue to create the same amount of water vapor, then this has to go somewhere.
    Logic suggests that if the treated area is both insulated and water vapor proof, then failing any changes like open windows, holes or dehumidifiers, then the water vapor will move as nature dictates.

  6. BobHr | | #6


    In a poorly insulated and drafty house you would likely be using a humidifer to add mositure to the air. With less leakage then your humidifier would use less water to get to the same RH. You insulated walls would leak less heat and the furnace would produce less heat. So really the same amount of heat, air and moisture will pass through the walls that was not insulated.

    Many people feel that furnaces dry out the air in the home. In reality it is the dry cold air pulled in to the house to replace the heated moist air that leaked out that is the cause of dry winter air. If you seal up the home enough you will stop using a humidifer and may actually have to start venting overly mosit air.

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