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Community and Q&A

Insulating Plaster and Tile Walls

churchguy | Posted in GBA Pro Help on

I’m looking at an old church to convert to a home, and trying to decide if I want to tackle the project. The church in question is a former Methodist church built in 1846. It is 34 x 44″ with no adornments, so it is a large open space with a roughly 16 ft. high ceiling. I’m assuming it is timber frame rather than balloon framed as it was strong enough to be moved onto a new concrete/ solid block foundation in the 1930’s to 40’s. They even put four 12″ I beams and columns under it so the foundation is solid. I don’t want to touch the exterior siding as it is original. The interior looks to have plaster walls, and it looks to be old 12 x 24 solid acoustical tile glued(?) to it. Believe it or not the tile looks to be in good shape.

Due to its size, I really don’t want to strip the interior plaster off. Just calculating the dumpsters full of plaster and the labor to do it gives me the shivers. Due to the size of it I’m not worried about losing floor space for a 2 bedroom house.

The big question is can I insulate over the old tile/ plaster interior walls without creating a moisture problem?

I’m in the middle of timber framing country, so SIPS are easy to get locally.  One thought was to install drywall faced SIPS horizontally to the tile, and screw it through to the timbers. My concern is that the painted tile might act as a second vapor barrier. The second is to frame the walls and infill them with Roxul with a 4 mil poly vapor barrier and drywall over it.

I’d welcome any info as I’m just not sure how to attack this project.

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  1. GBA Editor
    Martin Holladay | | #1

    I've never seen drywall-faced SIPs, but if you can get that product locally, and if the church doors are wide enough to allow the panels to fit through the door, that approach would work. I can't imagine that you'd have any moisture-related problems.

    You haven't described the original siding -- what type of siding is it? -- but if the siding is 173 years old, and it's still in good shape, I imagine that the existing walls readily dry to the exterior.

    For your plan to work, you need to make sure that your new thermal barrier (insulation plus air barrier) is continuous. That means paying attention to continuity at the floor-to-wall intersection as well as at the wall-to-ceiling intersection. Remember that your floor assembly will need insulation, and so will your ceiling assembly.

    Instead of SIPs, you could simply install interior rigid foam, followed by drywall or the finish of your choice. For more information on that option, see "Walls With Interior Rigid Foam."

  2. churchguy | | #2

    Thanks for your reply. 4x8 or 12 ft. panels will go through the door so no problem there.

    The siding is clapboard with many coats of white paint. Up here in New England you can find these old places, but finding one in the shape this one is in is a big plus.

    Some of these old churches weren't heated. Back in the day, when you attended services during the winter you dressed for that. The oil fired furnace was an addition later on with a new chimney built for it. Putting it on the new(er) foundation allowed for the addition of an event hall in the cellar, and a place for a heater. I spoke to someone who has 30 years of history with the church, and found that they cranked up the oil furnace on Saturday night so it would be warm for Sunday morning, and shut the heat down after Sunday services.

    I agree with you regarding the insulation. Blown cellulose in the roof to R50 or so, and the cellar walls will get foam board as well with a vapor barrier and new drywall.

    I'll be taking a good look at the place next week to nail down the details. Maybe I can get some pics posted.

  3. Expert Member
    Peter Yost | | #3

    Hi David -

    Insulating a building from the interior makes everything to the exterior colder so you need to ensure that moisture is being managed well. Small bulk water leaks that the building enclosure has been handling using the heat flowing through the assemblies can turn into problems. So, make sure you do a full assessment of the enclosure. Take a look at this GBA resource:


  4. ArfiePasana | | #4

    Buildings have been cared for, repaired, rebuilt, and restored at all times.

    1. LaverneDejardin | | #5

      Yeah and the restoration of churches and temples requires a thorough knowledge of modern building techniques and materials. The master must understand the methods of the architects of the old school. When restoring Catholic and Orthodox churches, the facade requires proper attention. Among the defects of the walls of church buildings, the most common is a breach of their moisture permeability. Moisture penetration leads to the destruction of the building material of the masonry. The selection of masonry material and mortar is particularly important during restoration work. According to all these and other parameters, the restoration of our church is finished

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