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Old 08-07-2017, 03:09 PM   #1
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Attic insulation in 80-90 year old farmhouse


Hello,
I have an old farmhouse that is probably 1930's era. The ceilings are bead board and ship lap. They are very non-airtight and allow communication between the air conditioned space and attic.

The previous owners put in fiberglass batt with the kraft paper face down against the ceiling in most of the attic. My understanding is that the kraft paper actually acts as a semi vapor and air barrier. It seems to do a decent job of insulating.

However, there is some flooring in the attic where they didn't insulate at all underneath it. My first thought was to blow in some fiberglass (like attic cat) or cellulose under the floor. However, I think there must be some sort of vapor/air barrier in place for it to be effective. I also don't want to create a cavity between the attic floor and ceiling that causes a condensation problem.

I am located in a hot, humid climate (Houston). The attic is unvented.

Am I left with taking up the floor and laying in fiberglass batt with kraft paper like the rest of the attic?

Any advise would be greatly appreciated. Thanks in advance.
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Old 08-07-2017, 03:44 PM   #2
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Re: Attic insulation in 80-90 year old farmhouse


You first need to decide where your thermal boundary will be. That boundary is made up of three elements, air barrier, insulation, and vapor barrier. The air barrier needs to be rigid and in contact with both the vapor barrier and insulation. The sequence of these layers is dependent upon the climate. In your hot humid climate the air conditioning will be on the inside so the air barrier and vapor barrier need to go to the outside so moisture (humid air) does not reach a cold surface. Air and moisture vapor pass easily through fiberglass insulation.

That ceiling is off to a poor start with the Kraft paper facing down. From your description there is no effective air barrier in place, typically a layer of drywall on the ceiling. Then, most of TX will require a minimum of R-30 insulation with N, NW looking for R-38, per the 2009 energy codes. Check local requirements.

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Old 08-07-2017, 04:24 PM   #3
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Re: Attic insulation in 80-90 year old farmhouse


This code may be for your location as well as Austin.

http://www.austintexas.gov/edims/document.cfm?id=109740
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Old 08-07-2017, 05:26 PM   #4
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Re: Attic insulation in 80-90 year old farmhouse


All, thanks for the replies. It seems like the code says there is a necessity for a "vapor retarder" in situations where you are not vented. So, I assume that is why the previous owners installed kraft faced fiberglass batts in the ceiling.

I hear what you are saying about the kraft paper needing to be facing up, but I don't think I have ever seen a house here in Texas where it was installed like that. Maybe it was supposed to have been.

From everything I read, it seems like I am stuck ripping the floor up and putting kraft faced batts in. The kraft paper isn't a "great" air or vapor barrier, but it is better than nothing. I am very limited in my options with the board ceilings I have.

Any other suggestions would be greatly appreciated.

Last edited by Joseph10; 08-07-2017 at 05:29 PM.
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Old 08-07-2017, 08:40 PM   #5
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Re: Attic insulation in 80-90 year old farmhouse


Here's a link that will help explain about vapor barriers and vapor retarders.
http://www.energyvanguard.com/blog/5...rrier-Probably

The Kraft paper as installed is probably doing little harm so I would hesitate to advise you remove it. And if code wants to see it then it is there. But energy science has grown to dislike vapor barriers (retarders) since we now understand that air leakage moves far more moisture than diffusion.
http://www.energyvanguard.com/blog/5...rrier-Probably

I'll let you read but IMO, you need an air barrier between house and attic and probably a lot more insulation. For consideration would be attic ventilation and the addition of a radiant barrier applied to the rafters.

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Old 08-14-2017, 05:20 PM   #6
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Re: Attic insulation in 80-90 year old farmhouse


Thanks for the info. I will check out the links tonight.
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