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Add ventilation to old attic?

Frost1 | Posted in General Questions on

Hi all,

I’ve read several of the blogs and articles regarding attic ventilation on this site and have searched through the Q&A section. I’ve learned quite a bit but am still a novice, and I haven’t quite found the answer to my specific question.

I purchased a 1912 Victorian about a year ago in southwest Ohio (climate zone 4A) and have slowly been making long-needed maintenance repairs and updates. Years ago the third floor attic was framed and converted to living space. There is zero insulation behind the knee walls, along the roofline, or in the ceiling steeple above – and no insulation I can see in the old attic floor (between he second and third stories). Additionally, there are no vents in place of any kind. Needless to say, the temperature up there quite mirrors outdoor temperatures despite meager attempts otherwise with baseboard heaters and window AC units.

We have no ductwork behind the knee walls, and while hot, the space feels dry and has not had any mold issues evident.

I found a reputable insulation contractor who will place fiberglass insulation and a radiant barrier along the knee walls and attic ceiling (and will blow fiberglass insulation along the roofline between) – at a seemingly appropriate R value for the climate.

My question relates to attic ventilation. He recommended talking with a roofer about adding some ventilation to the space – and that roofer recommended several box vents. I’m not in a financial position to re-do my roof yet (to add ridge and soffit ventilation if needed), though the roof is nearing the end of its life. From what I’ve read, I’m not sure box vents will do much, if at all. Nevertheless, should I add some ventilation to that space? Is there a risk to adding formal ventilation to a space that has been without for 106 years? Does adding insulation change the equation?

Thanks for reading and for any insight you can provide.

Best,
Andrew

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Andrew,
    When it comes to the sloped roof assemblies (cathedral ceilings), you can make these assemblies venter or unvented, as you choose, as long as you get the details right. For more information, see "How to Build an Insulated Cathedral Ceiling."

    For information on insulating behind your kneewalls, see “Two Ways to Insulate Attic Kneewalls.”

  2. Frost1 | | #2

    Hi Martin,

    Thanks so much for the quick reply and for the links - I had already had a chance to read those articles.

    Thinking about this some more, I guess my question relates to the impact of installing insulation against the knee walls and attic floor - that is excluding the attic from the thermal envelope - on temperatures in that space. Should I expect that the temperature and/or humidity will change (worsen) in the unconditioned attic as a result? I can't afford ideal ventilation solutions this year, so I'm wondering if I should expect problems if I just install insulation and don't address ventilation. Does that make sense?

    Thanks,
    Andrew

  3. GBA Editor
    Martin Holladay | | #3

    Andrew,
    Q. "My question relates to the impact of installing insulation against the kneewalls and attic floor - that is excluding the attic from the thermal envelope - on temperatures in that space. Should I expect that the temperature and/or humidity will change (worsen) in the unconditioned attic as a result?"

    A. First of all, there are two ways to insulate kneewalls and the attics behind kneewalls, as described in my article, “Two Ways to Insulate Attic Kneewalls.”

    But if your intention is to "exclude the attic from the thermal envelope" by installing insulation on your attic floor, you'll get these results: (a) You will save energy, because the insulation you installed will reduce heat loss through your home's thermal envelope, and (b) The attic will be colder in winter and hotter in summer than it was before you installed the insulation.

    If the work is performed properly, you won't have any moisture problems in your attic.

    For more information, see "How to Insulate an Attic Floor."

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