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Antique post-and-beam Colonial roof insulation

jambo13 | Posted in GBA Pro Help on

Looking for feedback on my antique colonial regarding insulating the roof. It is a large post and beam home built in the 1820’s in a suburb of Boston. The whole house: roof, walls, basement, currently have no insulation. I am renovating the home and plan to insulate it. About half the roof line acts as the sloped ceiling to the third floor (which is finished) and the other half is unfinished attic. There are two gable end vents providing airflow through the attic. My current plan is to remove the vents and clapboard over the holes. Then insulate between the plaster and lathe of the third floor ceiling with blown in cellulose, while spraying the exposed attic with open cell spray foam.  Should I be concerned about using two different types of insulation in this system especially considering I am removing the gable vents? Should I just remove the plaster on the third floor and spray that as well?  It is a great old house and the condition of the beams in the roof are perfect, I dont want to do anything to compromise them.  Thank you.

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi James.

    There are a number of ways to insulate a roofline. However, unvented assemblies with fibrous insulation alone or open-cell spray foam alone are typically not recommended. I recommend that you take a look at these articles:

    How to Build an Insulated Cathedral Ceiling
    Open Cell Spray Foam and Damp Roof Sheathing

    1. jambo13 | | #2

      Hi Brian,
      Thank you very much for your response and the articles for reference! I feel my situation is different than those referenced in the articles as it is not a cathedral ceiling application. I have drawn a picture here to articulate my problem more specifically. I am truly at a loss as to how best to proceed as I have brought multiple insulation companies through and they are not providing confident, thorough recommendations. Any information you could suggest would be greatly appreciated. Thank you, Jim

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