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Exterior insulation on 18th century log home?

jdlitt | Posted in General Questions on

I’m in the planning phase for a renovation on my families home. The main area of the house was built in the late 1700s using hewn logs and then covered with wood lap siding. A few decades ago someone covered this wood siding with aluminum lap siding. There are two additions at the rear of the original structure that were constructed with stick framing. 

My current plan for the rear stick built additions is to remove the aluminum siding, cover the sheathing with building wrap and then 2 inches of XPS foam board, add battens and then fiber board lap siding. 

The log section has me appropriately stumped. I would like to remove the aluminum and wood lap siding, install 2 inch XPS directly to the logs, battens and fiber board siding over that. Would this cause issues with vapor or water penetration? Would adding a layer of sheathing and house-wrap over the logs, then the XPS, then battens and siding be required?

A few more things that may help, the house is located in Kentucky a mixed humid environment. The perimeter log walls are covered with plaster and lathe on the inside. Any advice would be greatly appreciated, I don’t want to get the wall assembly wrong and cause major issues in the future. 

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  1. kbentley57 | | #1


    The north eastern and southwestern parts of the state vary a little, but generally I'd say that you would want to cover the bare logs with a separate weather resistant barrier first, as log homes are notoriously hard to air seal well. Tyvek, Typar, anything detailed well should work fine. Without the air sealing component, your insulation attempts will be significantly penalized. You probably don't need the sheathing.

    You didn't mention how planar the surface of the logs were. If they're mostly flat and in the same plane you're probably fine. If there are significant deviations in and out of plane (like a cyclic set of humps) then I would think those would need to be filled, somehow, before installing the exterior insulation. Any air space behind there is sub-optimal.

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