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Seal and insulate before considering venting?

Towsonite | Posted in Energy Efficiency and Durability on

If you have an older cape and it has both heat and moisture issues on the upper floor and in the attic and you have limited time and resources, would you first do your best at air sealing and insulating the house, and then evaluate whether those problems go away before considering venting the house?

I have a cape that’s ridiculously leaky (but I’m working on it) and virtually non-existent insulation (but I’m working on it). The heat upstairs makes the rooms non-useable during the summer. I still have lots of work to do, including a room by room gutting of the upstairs rooms. Once I get to the room by room gutting, I would leave sufficient spacing on the angled sections of the walls to allow a venting channel if I choose to do so in the future. But after reading the “All About Attic Venting” article from 2013, I may decide to forgo attempting to vent until I see whether my air sealing and insulation work (Plan A) solves the problems. If not, then I’ll go with Plan B of adding venting.

Somewhat related but not a problem I want to solve at this time is that I foresee issues with properly venting this house. So, even if I attempt to vent, which I don’t at this time, I may never get it to perform properly. The home is a “T” shaped cape and, as a result, I’d say at least 33% of the roof that could never be properly vented, meaning I can leave those angled walls open to the upper, central attic, but those rafter cavities dead end before reaching the lower, side attics. Also, because of exterior features and an addition on the first floor, soffit vents for intake will be limited.

Does that sound like a good plan of focusing on air sealing and maximum insulation, evaluating, and then and only then deciding whether or not to vent a home that has never been vented?

Thanks for your help!

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Jeff,
    You need to vent an insulated sloped roof assembly (cathedral ceiling) if you are installing certain types of insulation (fiberglass, cellulose, and mineral wool). The purpose of the vent channel is to reduce moisture buildup in the roof sheathing. This type of venting is required by building codes.

    The venting I have just described has absolutely nothing to do with lowering the temperature of your second floor during hot weather.

    So if you want to lower the temperature of your second floor during hot weather, concentrate on air sealing work and improving the R-value of the insulation.

    That said, certain insulation strategies require a ventilation channel between the insulation and the roof sheathing. That ventilation channel won't lower your second-floor temperatures -- but it will save your sheathing from disaster.

    Finally, if you prefer to insulate your sloped roof assemblies using an unvented strategy, you can. But if you are working from indoors, this method requires the use of closed-cell spray foam.

  2. GBA Editor
    Martin Holladay | | #2

    Jeff,
    For more information on these issues, see the following articles:

    How to Build an Insulated Cathedral Ceiling

    Insulating a Cape Cod House

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