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Community and Q&A

Insulating a Log Cabin Kit

bristolrog | Posted in Energy Efficiency and Durability on

We own a 1960 Log Cabin Kit near Lyons Oregon zone 4c. We would like to make it less dark and damp. It is surrounded by tall trees and ferns essentially a rain forest, very dark and damp except the south wall of huge windows looking over the river. Previous owners only used it in the summer and winterized it the rest of the year. We use it about two weekends per month, year around. We heat with a wood stove when there. We added a ceiling mount 220V shop heater in the main room set to 50 and use two 110v portable oil radiators in the bathroom and back bedroom by the wash machine. It has a good dry crawl space and we insulated the floor. This reduced winterizing the plumbing each visit, and sum-what reduce the wet log feel and smell. The 24×26 cabin is easy to heat when we light the wood stove. We are not looking for a lot of insulation but we want to reduce the “dark and damp”. The walls and ceiling are all exposed wood with dark stain. It smells like wet logs because it probably is wet logs.
The Square Log kit construction is similar but different than Robert Smith’s Kit posted 2/27/16. We have vertical 4×4 about 60” OC with an H grove, into which are stacked cedar 4×6 “square logs” with a double tongue and grove secured with 12” galvanized spikes. The 4×6 is the inner and outer wall. Stained on the outside and finished with a linseed oil?, Sticky seal on the inside. We re-stain the outside about every 2 years. We have altered the inside seal. Wiring is under the floor or wire-mold on the inside. Windows were single pane aluminum for the smaller windows and four huge single-pane plate glass windows in the main room with a single pane slider to the deck. We have already replaced the smaller aluminum windows with double pane vinyl. I think I can replace the plate glass windows and the slider without too much trouble.
This weekend we will try a white pickling stain over the linseed oil finish to lighten things up. I am not confident it will stick. I hate the thought of sanding the gummy finish off.
Adding insulation and sheet rock to the ceiling and walls is where I am worried about trapping moisture. The rooms are too small for 2×4 framing on the inside like Robert Smith was considering. There is barely room for a double bed now. Adding 1” Styrofoam to the walls then sheet rocking over it would be easy but I am worried about trapping water between the foam and the logs. We have been told that one of the neighboring cabins was a kit like ours, they added a full outside wall with conventional lap siding. We hate to lose the log cabin look. I am sure this is not the first log cabin to be insulated. Suggestions Please?
The roof was flat tar over 2x6TG fir supported by 4×12 beams about 60” OC perched on the 4×4 upright posts. The previous owner tore off the flat tar roof in the mid 90’s and installed metal at about a ¼”/12 over the 2×6. I don’t think there is any insulation or air ventilation under the metal. The TG 2×6 is the exposed ceiling, stained. We have some carpenter ant activity in the 2×6 fir ceiling and a little bit of rot on a few boards. I believe the rot was from the leaky tar before the metal roof. If we clear vegetation and spray the foundation religiously, the ants seem to disappear, temporarily.
I am considering adding insulation and sheet rock to the ceiling by firing down a 2×4 then adding 2” Styrofoam between the 2×4’s leaving 1.5” airspace cavity between the foam and the 2x6TG. Then hang ½” sheet rock to the 2x4s. This would leave about 7.5” of the beams exposed inside. I could bore through the 4×6 on each end of the ceiling cavity for ventilation. The roof has large eves on all sides. I am still concerned about trapping moisture in the ceiling and hiding the moisture and ant problems that already exist. The ceilings are high so we have more room for options than the walls.
The metal roof doesn’t leak, I hate to pull it off to repair or replace the 2×6. The cabin has weathered pretty well for nearly 60 years. I hate the thought of sealing it up tighter and having it rot out in the next 5 years. Suggestions Please? Roger Bristol

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  1. bristolrog | | #1

    These are photos of the Log Cabin Kit from Roger Bristol

  2. Expert Member
    Dana Dorsett | | #2

    Since it's only heated to 50F when you're not there the wood stays pretty damp.

    Keeping all interior doors open to the common areas and running a room dehumidifier set to 40-50% relative humidity would keep the wood reasonably dry, and would reduce the amount of heating energy used, since it would be taking the latent heat of the humidity in the air and converting it to sensible heat (warm air.) Set it up to automatically drain into a sink or bathtub so that it can continue to do it's job unattended, without anyone around to empty the bucket.

    Look for a basement type dehumidifier rated for operation at 50F or lower. Many cheap dehumidifiers will ice up when the indoor temp hits the low 60s or colder, which won't work in your application. You don't have to spend $500, for a low-temp unit, but you'll probably have to spend $250-300.

    Whether you insulate or not, mechanical dehumidification will mitigate the smell and the moisture risk to the logs by lowering the moisture content of the wood. If you're only fully heating it on weekends there isn't sufficient drying time to purge much moisture. A $30 box store 2-pronged wood moisture meter would be a good investment, and might help you find bulk water leak points, but would also give you an indication of how well it's working, even before the smell goes away completely (which could take awhile.)

    Insulating from the inside just keeps the logs in the colder-damper outdoors, which would usually increase the mold/rot/moss accumulation risk. Insulating it on the exterior would protect it from direct wetting by rain, and would keep the wood in the warmer-drier semi-conditioned space.

    If you can find a log-look siding or if ship-lap or mill slab siding suits your aesthetics, a layer of exterior foam strapped to the log wall with 1x4 furring, with the new siding mounted to the furring can work. Use roll type ridge vent mesh between the furring at both the top & bottom of the cavity to keep it from becoming a critter-condo, but venting it both top & bottom so that it can convect allows the new siding to dry into the cavity as well as the exterior, keeping it drier that it would if there were no cavity, or the cavity were blocked. Use metal bug screen at the openings as well.

    An inch or two of foil-faced polyiso or foil faced EPS would be greener than Styrofoam tm (= XPS) due to the differences in blowing agents used. The foil facer facing the 3/4" gap between the foil & siding adds a significant fraction of the total thermal performance at such low R-values, and is a vapor barrier blocking exterior moisture drives from reaching the susceptible logs. When used in conjunction with a dehumidifier this will keep the wet-log smell down, and protect the log structure.

    It may also be worth re-working the window framing to flash the windows to the outside of the foam, and/or add storm windows mounted co-planar with the new siding to keep bulk water intrusions at bay. Wind driven rain that hits the window would want to be directed to the exterior of the foam, and drain into the cavity between the foam & siding. There appears to be decent roof overhangs, but there will always be at least SOME rain that hits the windows. At the moment that rain hitting the windows drains onto the exterior of the logs, but if insulating on the exterior it's better to direct it outwards. A storm window at the siding layer would both improve thermal performance and comfort, while dramatically reducing or eliminating the amount of bulk moisture getting to the original window. Installing low-E storm windows would bring the total performance up pretty close to current code-minimums too, and would have a quicker "payback" on heating costs than uncoated clear storms, despite the somewhat higher up front cost of the low-E glazing.

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