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Suggestions for insulating a 1770s New England church building

Jon Michael Wyman | Posted in Energy Efficiency and Durability on

A local First Congregational Church (Climate zone 5) , established in 1770, is looking to use their building year round. Typically, it is too cold to use in the winter months due to no insulation and excessive heating bills.

The building has 22 feet high ceilings and a post and beam frame with bents some 10 feet on center and joists between. The timber frame is hidden in 8 inch thick balloon framed exterior walls. The frame sits on a stone foundation with a dirt crawl space that ranges in height from 1 to 4 feet. All walls originally were finished in plaster and lath, but many years ago were finished in decorative tin. Exterior walls are painted clapboards and a slate roof. Knob and tube wiring has been removed.

Sorry for rambling, but I felt the description important.

The plan for exterior walls is to remove the bottom rows of clapboards and clean out old plaster from the top of the sills. This will also allow blowing cellulose under windows. The remaining walls will be blown down from the attic.

The ceiling currently has a very small amount of blown cotton, animal scat and years of dust and dirt. The plan here is to vacuum clean between joists and add a thin layer of closed cell spray foam. The thought is the spray foam will air seal and adhere the lath and plaster to the insulation. We would then add loose fill cellulose.

The crawl space, at this point, will be spray foamed at the rim joist and protected with intumescent paint. At a later date, when affordable, the crawl space will have to be excavated to a point where a continuous layer of closed cell urethane can be applied.

Concerns for insulating an older building like the church have to do with wood framing showing through the exterior in winter and paint peeling with the new wall insulation. This isn’t so much of a question as looking for ideas or experience with similar situations.

Thanks for any help or suggestions.

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  1. GBA Editor
    Martin Holladay | | #1

    Whoever developed your insulation plan appears to have come up with a fairly good approach.

    Here are a few more comments:

    1. Before beginning your insulation work, it would probably be a good idea to hire an experienced weatherization crew to perform blower-door-assisted air sealing work. Considering the volume of the church, the building may require multiple blower doors.

    2. If the crawl space has a dirt floor, that floor should be covered with a polyethylene vapor barrier.

    Good luck with your project.

  2. Expert Member
    Dana Dorsett | | #2

    Most buildings of that vintage had the clapboards directly on the framing, without an intermediate sheathing layer. The empty cavities gave ample drying for the clapboards, any moisture that got in left pretty easily.

    If you fill those cavities with fiber insulation without any capillary break between the clapboards & insulation, the clapboards will run damp, the paint (or even the nails) will fail, and you're kinda screwed. This has been the demise of more than one antique church.

    There's also the issue of the probable lack of window flashing, and how to rectify THAT prior to insulating.

    Developing a better plan that still works is a bit hard to do via blogs- get a real building science type on site to poke around looking for trouble, and work-arounds.

  3. Jon Michael Wyman | | #3

    Thanks for the advice for moving forward in the investigation stages.

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