insulating top floor/attic of old house


Old 07-28-05, 08:26 AM
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Join Date: Mar 2005
Posts: 53
insulating top floor/attic of old house

I have an old house (1912) in a very cold climate (growing zone 3) with a half floor in the top. Basically this top floor is the attic with kneewalls and a ceiling, so the floor space is half of the other floors. I want to insulate and am trying to decide the most economical and effective way to do so. So there are vertical walls, sloped ceiling and horizontal ceiling to think about. My questions involve the relative efficiency of insulating horizontal and vertical surfaces (ie. behind the kneewall), versus insulating the slope. I know if I insulazte the slope, I will have to add 2X4s to increase the cavity space and also provide space for air flow behind the insulation and a vapor barrier on the warm side. Obviously, I will need to use this appraoch for the section which has a sloped roof on the interior. Should I use this approach for the whole ceiling, or should I use it only where the ceiling is sloped, and insulate the vertical and horizontal surfaces behind the kneewall and the horizontal surface of the flat part of the ceiling instead of insulating the sloped part in these areas ? This would allow for thicker insulation on the horizontal surfaces and eaiser access to the insulation to see if there are ventilation problems etc., but it would complicate the vapor barrier considerably, since it will be changing direction at several points. Also with regard to the vapour barrier, I have access to the underside of the flat part of the ceiling (where the top of the sloped ceiling ends), since I will replacing the plaster, but I do not have access to the bottom of the horizontal surface behind the kneewall (this is part of the ceiling for the floor below. I have read that a vapour barrier is not necessary for a ventilated atic space and am wondering if this applies in my case to the space behind the kneewall and the smal attic above the flat part of my ceiling. If I do need a vapour barrier for the horizontal surface behind the kneewall, can I simply drape it over the joists? Since I have not bee back there yet, it may even be that the room flooring extends behind the kneewall and I won't even have access to the joists. In this case, can I simply lay vapor barier over the flooring and seal it at the edges, laying the insulation on top? I know there are a number of questions here, but would be grateful for answers to any of them. Please let me know if I can clarify anything, as it is very difficult to describe the situation in writing.

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Old 08-07-05, 04:51 PM
Join Date: Nov 2001
Location: USA
Posts: 1,873

Very brief description of attic access insulation. The last section illustrates and describes the way to insulate behind knee walls. If this does not do it for you, post again.

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