Insulation
Hi. I am trying to renovate a 65 year old house. It is a 2 story house. The second story has a 4 foot vertical wall and then it turns into the roof. The slope is about a 10/12 slope. What I would like to know is whether or not I should treat the slope as a wall or as a roof for insulation purposes? If it is to be treated as a roof would I have to leave space for airflow? Right now I have diagonal cross bracing between the rafters. If I need air flow I would either have to remove these braces or drill holes through them. I was thinking about drilling the holes and then placing Tyvek house wrap over the existing rafters and then building a new set of rafters on the inside of the house. Then place 6 inch batting insulation between the new rafters and holding it in place with vapor barrier. Would this be the proper way? Thanks.
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Replies
Floyd,
Q. "What I would like to know is whether or not I should treat the slope as a wall or as a roof for insulation purposes?"
A. It is a roof.
Q. "If it is to be treated as a roof would I have to leave space for airflow?"
A. There are two ways to insulate sloped roof assemblies: you can make these assemblies vented or unvented. To learn more about all your options, see How to Build an Insulated Cathedral Ceiling.
Q. "I have diagonal cross bracing between the rafters. If I need air flow I would either have to remove these braces or drill holes through them. I was thinking about drilling the holes and then placing Tyvek housewrap over the existing rafters and then building a new set of rafters on the inside of the house. Then place 6 inch batting insulation between the new rafters and holding it in place with vapor barrier. Would this be the proper way?"
A. Not really, for a variety of reasons, including the following: (a) Your method takes up a lot of interior room; (b) Your method introduces new rafters, which act as thermal bridges that lower the insulation value of your roof, (c) Batt insulation generally performs worse than rigid foam insulation, and (d) An interior vapor barrier is usually a bad idea. I suggest that you read the article I linked to for some better ideas.