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Community and Q&A

Air intake for a 70 year old Cape Cod with knee walls

MptjgNPKTm | Posted in GBA Pro Help on

I have a 70 year old Cape Cod with a finished upstairs. A few years ago a steel roof was applied over the existing roof. The contractor put in a ridge vent but I have no air intake. I have 2*4 framing with 1″ insulation. What suggestions do you have for getting some air intake into this space ? Gable vents ?

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  1. GBA Editor
    Martin Holladay | | #1

    It isn't clear that you need soffit vents. If it's true that your roof has only 1 inch of insulation, you have many issues to address before you have to worry about ventilating your rafter cavities.

    If you are interested in improving the thermal performance of your house, and if you have some money to invest, I advise you to hire a home performance contractor to provide an energy audit. A contractor should be able to advise you of the best way to add more insulation (and perhaps to seal air leaks) in your home.

    Good luck.

  2. MptjgNPKTm | | #2

    Thanks for responding. My finances are limited. Let me clarify this I have 1" of insulation behind the slope of the knee wall. It appears to be wool between black tar paper. I have 4" of insulation on the floor of my attic and want to add more. But before I add more insulation I was going to address the issue of ventilation so that I can be certain that insulation won't be blocking my intake vents. I was considering putting round vent inserts in the soffits but from what I have been reading this will cause the insulation to absorb moisture and the use of baffles were recommended. The problem with 2*4 construction I don't have the space to slide baffles behind the slopes. This is why I am looking for suggestions. Can I get away with using soffit vents without the use of baffles? My attic doesn't appear to have any rot or mold it is just that the 2nd floor bedrooms are hot. I know having a 70 year old house doesn't provide me with the greastest thermal performance but I am trying to make small improvements.
    Thanks Brenda

  3. GBA Editor
    Martin Holladay | | #3

    Adding soffit vents will not solve your hot-bedroom problem.

    Your bedrooms are hot because you have so little insulation in your house. To solve your comfort problem, you need to upgrade your insulation. You may also need to use fans or even an air conditioner during the summer, even after your insulation is improved.

  4. MptjgNPKTm | | #4

    So even though I have a ridge vent, do you recommend that I not worry about any air intake and increase the depth of insulation?

  5. GBA Editor
    Martin Holladay | | #5

    I recommend that you get an energy audit so that you can formulate a plan for increasing your insulation thickness. Before that happens, there is no need to worry about your soffit vents. After all, you told us, "My attic doesn't appear to have any rot or mold."

    If you can afford to improve the thickness of your insulation from its current level (probably about R-3.5 in the sloped area and R-14 on the attic floor) to something closer to R-38 or R-60, you'll need to decide whether to choose an unvented roof assembly or a vented roof assembly. Either approach can work fine. To learn more about different ways to insulate a sloped roof, see How to Build an Insulated Cathedral Ceiling.

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