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Community and Q&A

Insulating sloped ceiling in old house

user-249719 | Posted in Energy Efficiency and Durability on

We are reinsulating the attic of our 100 year old home but are dealing with a difficulty. The top floor has a sloped ceiling from about five feet high to the flat ceiling. When we bought the house, the previous owner had stuffed this from the attic area with batt, which had blocked the soffits and caused premature aging of the roof. We unblocked the soffits, reroofed and added a ridge vent. We are now in the process of replacing the wood shavings and need to be able to insulate this area. We were planning to do spray foam but have been told they would need to rip out the dry wall of all the sloped areas (four bedrooms, three closets and a bathroom!) in order to do it properly. The problem with this (aside from the obvious increased work and cost) is that the drywall is over plaster which has been a misery to deal with in other parts of our renovation. We need a solution we can install from the attic area that includes a vapor barrier and the best degree of insulation we can achieve. We have been advised to install baffles from the soffits and expect this to cause some space issues though hoping we can somehow insulate around either with blow-in, batt or insulation board? We have been advised to use a paint on the ceiling of the top floor to provide a vapor barrier as this area is so inaccessible. Does this make sense? Should we ditch the idea of spray foaming anywhere and just go with batt, blow in or cellulose? We live in Calgary so have very cold periods in the winter so are looking for our best option. The house walls were wrapped from the outside at some point with insulation board I believe. Thanks for any advice!

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  1. GBA Editor
    Martin Holladay | | #1

    Here are some links to relevant articles:

    How to Build an Insulated Cathedral Ceiling

    Insulating a Cape Cod House

    The contractor who told you that the best way to insulate these sloped areas is to first remove the drywall ceilings gave you good advice.

    If you want to insulate the roof entirely from the exterior, you can. The only problems with this approach are these: (a) you need to install new roofing, and (b) it's expensive. Here is a link to an article with more information on this approach: How to Install Rigid Foam On Top of Roof Sheathing.

    You wonder whether it's possible to slide some type of ventilation baffle down these rafter bays, working from the attic above, and to follow up that work by insulating between the ventilation baffles and the ceiling without removing the ceiling. The answer is "generally, no," but if the sloped areas aren't too long, and the attic is big, it might be possible. Here is a link to an article about ventilation baffles to inspire you if you want to get creative and try this (generally difficult) technique: Site-Built Ventilation Baffles for Roofs.

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