Add fan for circulation WITHIN attic?

Discussion in 'Home Repair' started by Nexus7, Oct 13, 2005.

  1. Nexus7

    Nexus7 Guest

    I've come across a situation that seems unlike any I've seen discussed
    here, but this is probably common in 30-40 year old houses. This is an
    approx 20x80 sq ft raised ranch (a basement and 1 floor of living
    space) with a hip roof. The attic has loose fill fiber, about 4", but
    it's pretty uneven and dusty (30 years will do that). In addition,
    insulation has settled deep into the bathroom and kitchen walls, so
    that if the vanity cabinet in the bathroom is removed, the bathroom
    wall is open to the attic. There's a ridge vent running along the
    middle 2/3 of the length of the ridge, and 3-4 passive vents halfway
    down the roof. While adding some batts seems an obvious way to increase
    the efficiency of the roof, there are two problems.
    - the hip roof overhangs about 3 ft in the front of the house, and this
    is the only place where there are 2 soffit vents
    - with the lack of soffit vents along the other 3 sides, air may short
    circuit between the ridge and passive vents

    I was wondering if, after adding another 8" of batts, it makes sense to
    have a small (6 or 8") fan going at low speed, at around half the
    height of the attic. This could circulate the air enough that moisture
    (and heat in the summer) would circulate with the outside air through
    the vents.

    Also wondering if laying some Tyvek before laying down the batts where
    the roof is open to the walls of the living space would be advisable.
    Nexus7, Oct 13, 2005
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  2. Nexus7

    SQLit Guest

    Google for R values for your area then you might be able to make some

    I just added R-30 of blown to a 1977 home. A/c bill dropped in half the
    next month.
    According to the FEDS, My home needs, either R-30, R-38 or R-43. I elected
    to go toward the top and not the bottom. New homes here come with R-30.

    Circulation of the air in the attic seems like a dumb idea to me. You have a
    ridge vent, so as long as you have enough sq inches of supply air the ridge
    vent should do the rest for ya.
    SQLit, Oct 13, 2005
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  3. Nexus7

    Bob Guest

    I suspect this would just kill any natural ventilation which would occur.
    Plastic maybe. Not Tyvek. Tyvek allows moisture to pass into the insulation.

    Bob, Oct 13, 2005
  4. Nexus7

    m Ransley Guest

    There are rigid foam baffles you staple to the roof deck at the
    overhang that are designed for adding more insulation without stoping
    the airflow in from the soffit vents, cheap and easy to instal.

    A fan will do nothing, forget it.

    R values are minimums for code. 4 of what you have + 8 will be apx R
    42. Optimal anywhere cooling or heating is needed as a major cost yearly
    is R 60+. Insulation settles, I put in R 100 a few years ago, now it is
    apx R-80. Once you are doing the work the exrtra insulation is cheap. I
    am zone 5 to - 20f.
    m Ransley, Oct 14, 2005
  5. Nexus7

    Nexus7 Guest

    Depending on the conditions and source, anywhere from R-38 to R-49.
    Seeing a show I have 4-5" of very old and patchy fill, adding R-25 or
    more would probably make a big difference; but the devil's in the
    Well, there are no soffit on 3 sides, so the fan was to utilize the
    combination of ridge and the 2 existing soffit vents better. However
    the roof has come through for two years as it is, so perhaps it is best
    to leave well alone.
    Nexus7, Oct 14, 2005
  6. Nexus7

    Nexus7 Guest

    Very little of the living space is open to the roof, so I could add
    plastic only there, and the rest of the space doesn't have any vapor
    barrier. Since it was finished 30-35 years ago, there are imperfections
    due to remodels, repairs in the intervening years, and so instead of
    sealing the interior, I was thinking of providing a way to escape for
    the moisture which will make it's way into the walls and roof.
    Nexus7, Oct 14, 2005
  7. Nexus7

    Nexus7 Guest

    The problem is that there are only 2 1x2 sq ft soffit vents in the
    front, and no vents on the other 3 sides. The roof has no overhang, so
    there isn't any space to retrofit soffit vents.
    Was this fiberglass or cellulose? I was thinking of batts, then after
    reading some, I was leaning towards cellulose and Home Depot's rental
    blower. Only worried that the moisture from cracks, etc. in the old
    walsl and ceiling would saturate the cellulose.
    Nexus7, Oct 14, 2005
  8. Nexus7

    Nexus7 Guest

    The roof has no overhang on 3 sides, so no soffit vents can be added. I
    can clear up the two at the front, but something else would be needed
    for the other 3 sides. On the other hand, the roof components are in
    good shape, so whatever is there isn't too bad to begin with. The
    suggestion fo the fan was to mitigate the short-circuiting of the ridge
    and passive vents.
    They're suggesting new batts all around and that's it. Given that the
    roof made it all these years, maybe that is the best course of action.
    Nexus7, Oct 14, 2005
  9. Nexus7

    Bob Guest

    I just added lots of fiberglass batts, and it made a huge difference in my house. The more the better, I'm sure. I did
    plug the tops of some walls that opened into the attic with plastic bags stuffed with scraps of insulation.

    I have thought about adding plastic or something to the underside of the rafters in my attic. It would go from low in
    the attic (but open at the bottom) to the top, thus forming a natural convection path to the ridge vent which would be
    fed by sun heat on the roof. There would be guaranteed air flow under the roof deck in the areas where this is done.


    Bob, Oct 14, 2005
  10. Nexus7

    Goedjn Guest

    If you can't conveniently vent the eaves/soffits (because there
    aren't any) and you're not willing to give up on vents entirely,
    which is what I'd do, then you do need to mechanically drive outside
    air into the the attic somewhere.

    Is there some reason why one can't lay PVC drain-tile around the
    perimeter, and use a high-volume fan to force air from any convenient
    source through it? Would one have to run a grounding-wire inside
    the pipe, or is that just when you're using it for dust-collection?
    Goedjn, Oct 14, 2005
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