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OT: Cooling your home with roof space / loft / attic ventilation.

Discussion in 'Electronic Design' started by Eeyore, May 24, 2007.

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  1. Eeyore

    Eeyore Guest

    I recall some of the US contributors here mentioning a way to help keep the
    house cool by actively ventilating the roof space.

    With my room temp here upstairs at the sunny front of the house currently @
    26.3C and outside air temp @ 25.4C (touched 30 yesterday) I'd like to do
    something along these lines to minimise using (with the associated electricity
    use) the a/c I have now.

    Can you point me in the direction of the stuff that's sold over your way to do
    this please ? I can't find anything in the UK but it would help if I knew what I
    was looking for !

  2. GregS

    GregS Guest

    If you have attic space, its easy. I have been insulating here and there. I'm even advertising
    here and there, but received no payments yet. I was using some aluminum backed polyethelene
    foam in the basement, because the foam insulation boards requred drywall protection
    due to fire issues. I used fiberglass in back of the stuff for better insulation on one side
    of the basement, and two layers of just the foam on the other side. The foam does not absorb
    moisture. On layer up against the brick and another layer spaced out about an inch. This
    eliminates any IR radiated heat flow. So, I bought some foil sheeting thats preforated for use
    in the garge. Under the roof spaced about 5 inches out on the supports, I stapled the foil covering
    the entire roof. You feel no radiated heat from the roof unlike what it used to be like.
    It even insulates a bit with just the airspace. This tough foil like product is preforated,
    and can be used on top of attic insulation to reflect any heat back onto the roof. It
    can make a big difference. The Prodex stuff probably has an R value of 1 to 2, but the IR
    factor adds a couple more. If used with air gaps, its a lot more. The thin foil I used does
    not tear, but is only a barrior except for the preforations.

    See my Goldstone page.....

  3. Noway2

    Noway2 Guest

    You are correct about ventilating the roof as having become a standard
    practice in the US. This was done as an upgrade in my first house,
    which was about 80 years old, and as part of the new construction of my
    current house.

    There are a few different options available that you could implement (or
    not). These include: a roof vent at the peek of the roof, which
    consists of a form of membrane that lets the air out, but is water tight
    and has a peak shield as part of the assembly, active fans that are
    thermostat controlled that will force the hot air out, and roof vents
    that are simply weather proof covers that you can put in the roof,
    similar to the fans but not as effective. My parents installed one of
    the thermostat controlled fans and noticed a definite cooling effect int
    heir house.

    Another factor to consider is that for proper cooling, you will need to
    get air into the attic space. This is done with a form of baffle that
    goes in the eaves to allow an air gap between the roof and the
    insulation. In older houses, it is also usually necessary to cut an
    opening in the eaves as they are more than likely solid. Newer siding,
    mostly vinyl, allows for the air flow.

    In any case, you will also want to make sure that you install proper
    flashing to prevent water leaks.
  4. There are electric ventilation fans with a built-in thermostat that
    turns them on above a certain temperature. Don't know the brands

    Best regards,
    Spehro Pefhany
  5. Mike Monett

    Mike Monett Guest

    Lots of houses here use wind-driven turbine ventilators. They seem to
    survive the harsh weather quite well:


    Mike Monett
  6. I have put a few of these in for friends and relatives. They start at
    about $50 US each for the horizontal axis models intended to mount
    behind a gable vent.

    Some years ago, I stuck a thermocouple in my attic, connected to a data
    recorder. On a sunny day in Seattle, with 75 °F outside, the attic could
    reach 130 °F. Even a good layer of insulation will only slow that down
    from heating up the living space.
  7. Search for attic fan, or PAV, or powered attic ventilator, or whole house

    See for some
  8. default

    default Guest

    New construction in my area uses a continuous perforated soffit along
    with a continuous roof peak vent (leaves an opening of ~2" along the
    whole of the peak. Strictly passive, effective, quiet and maintenance

    My house is older and has vents in the sides at the peak, but no
    soffit openings. Front and rear have inset doorways and I cut 2' X 4'
    holes in them and mounted some SS grills that came out of an
    industrial plant air intake. That lowered the heat 25 to 30 degrees F
    in summer.

    My wife went for a pair wind powered turbine vents on one roof slope.
    She has no soffit vents and it is not significantly cooler with just
    the turbines - needs a way for fresh air to get in - the vents only
    exhaust air.
  9. They are called "whirlybirds" in Australia and almost every Aussie
    home has a couple.
    Contrary to popular belief they are not "wind driven", they have very
    smooth bearings and the rising heat is enough to turn them, no need
    for any wind.

  10. John Ferrell

    John Ferrell Guest

    Home Improvement stores in the US carry the thermostat controlled fans
    for about $50. After the fan motor failed on the one I have in the
    garage I replaced the fan assembly with one from a replaced heat
    pump. I did not duct it tightly so there is a lot of air circulation
    in the attic area.

    John Ferrell W8CCW
    "Life is easier if you learn to
    plow around the stumps"
  11. If that were so they would not be needed as they impede airflow. It takes
    energy to move them.
  12. No icing in winter? With no soffit vents you are asking for ice dams in cold
  13. Eeyore

    Eeyore Guest

    I wondered about that. It makes sense.
    A little.

    The important thing is that they keep the rain and birds out. A hole in the roof

  14. Yes it does, and the energy comes from the rising heat.
    Wind does help in the efficiency, but is not required for them to
    They are needed because they are more efficient than a simple hole in
    your roof (due to vortex's and such) even with the extra energy
    required to drive them, while at the same time keeping out rain.
    I've seen simulation models of the airflows and some designs are very
    advanced in this respect, much research has gone into them.

  15. default

    default Guest

    Global warming? This past two years we haven't had real frost. Ice
    in winter? She has 4 chords of wood that are 10 years old.

    Used to be; the ground froze two feet deep in winter, and one spent a
    lot of quality time snuggling with the wife - we still open the
    windows and turn on the fans but it ain't the same somehow. I still
    want the wife and snuggling.

    But shouldn't complain - no mosquitoes, "no see ems" and it is late

    Perhaps if this continues for a few more years we can grow tomatoes
  16. Rich Grise

    Rich Grise Guest

    But when the wind _does_ blow, they turn into centrifugal turbines -
    almost like suction pumps.

  17. Eeyore

    Eeyore Guest

    Do they really ? I suppose they might do that

  18. Yes, and that's the real point.
  19. Eeyore

    Eeyore Guest

    So it's better to have electrically powered fans that only run when you need
    them then ?

  20. GregS

    GregS Guest

    I just installed another attic fan when I had the airconditioner installed
    in my new, old house. They are very handy for getting fresh air in and
    getting cooling when you don't have to use the air. I even use it to help
    clean the house. I turn the fan on high and get out my gasoline air
    blower and shower the house. I see cat hairs everywhere. The problem with attic fans,
    most I have seen are cheap and don't have much control of the speed. High sounds
    like a turbine. I install Green Plugs on them to slow them down a bit.

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