OT - Need to ventilate an attic with hip roof - powered roof vent?
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  1. #1
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    Default OT - Need to ventilate an attic with hip roof - powered roof vent?

    Title says it - should I install a powered roof vent or is there another approach? If so - any quality products?

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    turbine ventilator no need to run a power line inside a 150 degree attic. the hotter it gets the better it works.
    For a hip roof the classic is a cupola with louvers on all four sides.
    Bill D

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    You'd also need a way to get air into the attic, like soffit vents.

    Not quite sure what you mean by hip roof, as it has different meanings in different parts of the country. In Indiana, it means a double pitched roof with no gables. In New England it often means a gambrel roof.

    Continuous soffit and ridge vents the best. May not be so easy to retrofit, though a lot less maintenance than anything with moving parts.

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    soffit vents are a given

    2nd the ridge vent if you can match the shingles

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    We had an attic exhaust fan. Failed after only a couple years. Not a fan (heh hee, sorry for the pun). We had the fan removed and the hole plugged and a new roof over the top of it, with ridge vents installed. With adequate soffit vents, this works great. If your situation allows this, I'd strongly recommend going with the passive ventilation.

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    Have to add another vote for ridge vent. I did ridge vent and continuous soffit vent to match years ago. I also put 1/2" foil faced rigid insulation a couple inches below the inside of the roof sheeting so any heat coming through the roof is trapped in the space there and directed out the ridge vent. In full sun in the 110º summer the attic is only a few degrees above ambient temp, maybe 115º. Before doing this attic temp would be 150-160º

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    Assuming you have vented soffits, the current wisdom is to use passive ventilation from the soffit up through a ridge vent. That is what I did and I have a typical gable roof with soffit in front and back. It is also advised to close off the gable end vents, as it messes with the flow of air from the soffit to the ridge.

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    Quote Originally Posted by Bill D View Post
    turbine ventilator no need to run a power line inside a 150 degree attic. the hotter it gets the better it works.
    For a hip roof the classic is a cupola with louvers on all four sides.
    Bill D
    Turbine ventilator? I take it you either have a dozen of them or never go in the attic, those things are next to useless.

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    Hip roof is a four sided roof that comes to a point. Ridge vents on that type, not so good. I'm ready to install
    a small dormer on my garage to provide ventilation at the top. Summertime you can practically smelt iron up there...

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    Quote Originally Posted by Dualkit View Post
    Turbine ventilator? I take it you either have a dozen of them or never go in the attic, those things are next to useless.
    14" is rated at around 700 CFM. I have three on my house. they do vent more then a 14" hole since the fan acts as a pump. Even in still air it will rotate if there is enough heat difference inside/outside.
    Bil lD

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    Quote Originally Posted by Bill D View Post
    14" is rated at around 700 CFM. I have three on my house. they do vent more then a 14" hole since the fan acts as a pump. Even in still air it will rotate if there is enough heat difference inside/outside.
    Bil lD
    I am guessing that is three 14" turbines in not a very big attic. Even if it worked I would rather run wires to a couple gable fans using existing gable vents than cut 3 more holes in a roof that can lead to leaks. What is the trouble with putting a couple more wires in an attic? You don't wait till high noon in the middle of July to put them in. My job is going to be way faster and easier than yours.

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    You asked for alternatives so here goes.

    When I was growing up in New Orleans (heat, humidity to the max), before air conditioning, we had a whole house ventilation fan installed in a central hall. It blew air into the attic and then outdoors from a large vent on the porch. That cooled both the house and the attic.

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    They make solar powered ventilators (14") that need no AC wiring to work.

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    Quote Originally Posted by EPAIII View Post
    You asked for alternatives so here goes.

    When I was growing up in New Orleans (heat, humidity to the max), before air conditioning, we had a whole house ventilation fan installed in a central hall. It blew air into the attic and then outdoors from a large vent on the porch. That cooled both the house and the attic.
    Yup, my grand dad had one of those. It was a big fan in a small house. When it was on it was hard to open the front door if a window was not opened first---a fact he enjoyed demonstrating even though the whole idea was, obviously, to have the windows open for maximum draft. It was very effective. I have a 110 powered gable fan that makes a huge difference. It is thermostatically conrolled. (Unfortunately it does not affect opening the front door! ) Seeing what that fan did for my house, my neighbor recently added one to his.

    Denis

    Added: Oh yah, my entire hose is solar powered, not just the fan.

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    Quote Originally Posted by dgfoster View Post
    Yup, my grand dad had one of those. It was a big fan in a small house. When it was on it was hard to open the front door if a window was not opened first---a fact he enjoyed demonstrating even though the whole idea was, obviously, to have the windows open for maximum draft. It was very effective. I have a 110 powered gable fan that makes a huge difference. It is thermostatically conrolled. (Unfortunately it does not affect opening the front door! ) Seeing what that fan did for my house, my neighbor recently added one to his.

    Denis

    Added: Oh yah, my entire hose is solar powered, not just the fan.
    Worked well in Pennsylvania and Virginia, too. Quite common until central air became pretty much standard.

    Grainger & c. still sell them, and with fusible-link louvers so they (are meant to) seal-off draft if there is a fire.

    Most I've used were belt-drive, so their motors can be chosen for whatever your solar system offers.

    The end-gable-types and through-roof types? Mixed reviews. I inherited three, seldom use them, still need something better, myself.

    Same age and type overheated its motor, set fire to a house just four doors up the street, took out nearly a third of the structure even with the Sterling VFD less than 800 feet away and on-scene about as soon as can be ..... once the fire was DETECTED ....which was not immediately...

    Here's an example as may explain why they are not the best idea:

    The #1 Reason Power Attic Ventilators Don't Help

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    The reason attic fans don’t work is they draw air conditioned air into the attic?!

    Could be true if we needed air conditioning. But I live in the PNW where summers are generally pretty mild. Secondly, the fan and other passive measures we take makes an air conditioner unnecessary. The obvious brute force approach is to either install energy-sucking refrigeration to overcome the ridiculous design of most houses or to essentially cook in the solar heat collectors we call houses. A third option is to figure out how to reduce solar gain. That won’t be the full answer for people living where summers are brutally hot, but better design can make your roof and attic act like an umbrella rather than a toaster oven.

    Denis

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    Here is very good info on attic ventilation, what it does and why it is important to get it right. Details pros and cons of all types of attic vents.
    https://www.airvent.com/index.php/ve...on-course/file
    Best thing to do is as I did in post #6, do not let the heat in in the first place. Icehouse roof is another name it.

    Funny story: A buddy of mine moved into a rental house that had a whole house fan, the kind that blows air from inside the house into the attic to force out hot attic air. He knew that some windows needed to be open but for some reason did not open them on this particular day. The fan drew air down the chimney as it had to come from somewhere, bringing with it all the ashes that were in the fireplace in about a 10 foot path out into his living room.

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    Quote Originally Posted by dgfoster View Post
    better design can make your roof and attic act like an umbrella rather than a toaster oven.

    Denis
    Bingo.

    There have long been better designs, roof UNDER another roof "free" air isolating system as well as pay-for-it insulation high on the list.

    Saving my pennies to replace my dark coloured and VERY much over-age-in-grade asphalt shingle "roofover" with light coloured aluminium shingles, reflective layer under as well.

    "Meanwhile" an experiment with greatly expanding the area for inflow - soffit off, under-eave area wide-open for a year now - has worked very well at reducing heat that reaches the living spaces.

    Wintertime heat LOSS we have pretty well under control by now. As we get the summertime heat input reduced, comfort continues to improve, costs are still dropping.


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