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  1. #1
    Join Date
    Nov 2008
    Posts
    1

    Default Ventilation/Insulation of Enclosed Attic Space

    We have a 1924 duplex in Washington, D.C. and we are in the process of renovating our attic. We are concerned about proper ventilation and insulation between the area we want to use as living space and the mansard roof which is mostly flat, but peaks towards the front and side.

    Do we need to create an air space between any insulation and the roof? or can we simply put in insulation with vapor barrier in the ceiling, and not worry about ventilating behind the insulation?

    If we do need to ventilate, where does the air go? We don't have a true peak where we could let air escape that way. We could create a space that connects to the unused attic space which is at the flattest part of the roof, but since heat rises, would that merely push the air up to the highest point with no escape? There are soffits on the front and side of the house which we could vent, but again, the air could only go in one direction, up, to the peaked part with no escape.

    If we have an attic fan in the unused portion will that be enough to draw heat out?

    Any advice is greatly appreciated.

  2. #2
    Join Date
    Aug 2008
    Posts
    54

    Default Re: Ventilation/Insulation of Enclosed Attic Space

    Quote Originally Posted by MLudwig View Post
    We have a 1924 duplex in Washington, D.C. and we are in the process of renovating our attic. We are concerned about proper ventilation and insulation between the area we want to use as living space and the mansard roof which is mostly flat, but peaks towards the front and side.

    Do we need to create an air space between any insulation and the roof? or can we simply put in insulation with vapor barrier in the ceiling, and not worry about ventilating behind the insulation?

    If we do need to ventilate, where does the air go? We don't have a true peak where we could let air escape that way. We could create a space that connects to the unused attic space which is at the flattest part of the roof, but since heat rises, would that merely push the air up to the highest point with no escape? There are soffits on the front and side of the house which we could vent, but again, the air could only go in one direction, up, to the peaked part with no escape.

    If we have an attic fan in the unused portion will that be enough to draw heat out?

    Any advice is greatly appreciated.
    What is the pitch where it does peak? How much space is there between the insulation and roof? If it is not much, perhaps a dense packed insulation is the best answer and would not require venting. If you have enough room and pitch ( 4/12 or steeper ) install roof vents near the peak. For high/low venting - square footage divided by 600 times 144 will give you the net free vent area you will need in square inches.

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