Log and Timber Frame Homes

Why this matters

A log wall gets shorter for years after it is built, and almost nothing else in the house does. Every pipe, wire, duct, door frame and partition that is fixed at one end and tied to the logs at the other is in a slow tug of war, and the logs win. The drain that starts leaking in year three, the door that will not latch, the cracked drywall at the top of an interior wall and the gas line pulled tight at its appliance are usually the same problem, and a tech who repairs the symptom with a rigid connection sets up the next failure. Read the house's movement before you fasten anything to it.

Why log walls settle, and how much

A log wall loses height for two reasons. Shrinkage: wood shrinks across its grain as it dries toward the moisture content of the house, and a log wall is stacked across the grain from bottom to top, so every course loses a little height and the losses add up. Compression: the logs crush slightly at their joints and settle into each other under the roof's weight. Together these are called settling.

How much depends on how dry the logs were when they were stacked, the species and the profile. Log home builders publish a settling allowance, a figure per foot of wall height, and the range between green logs and kiln-dried logs is wide. Use the figure from the builder or log supplier for that house, which is often in the original package documents or on file with the builder; if there is none, treat any figure as unknown rather than borrowing one. Most of the settling happens in the first few years, then it slows, and seasonal swelling and shrinking continues for the life of the house.

Timber frame is different. A timber frame carries the roof on a skeleton of heavy posts and beams, and the walls are usually an enclosure of structural insulated panels (SIPs) or conventional framing wrapped around it. The posts are loaded along the grain, where wood barely shrinks, so a timber frame does not settle the way a stacked log wall does. The beams still shrink and check across their thickness, joints loosen and tighten seasonally, and a hybrid house with log walls on one floor and timber frame on another can move unevenly between floors.

How the original builder left room for movement

A well-built log home is full of deliberate gaps. Learning to see them tells you where movement is expected and lets you check how much has happened.

• Settling space above windows and doors. Openings are framed with a buck, a frame set into a slot in the log ends so the logs slide down past it. Above the header, a gap packed with compressible insulation and hidden by trim lets the logs come down without crushing the window. When that gap closes, the next thing to give is the window.
• Slip joints in interior framing. Conventional stud partitions meet the logs through a vertical slot. The top plate or a fastening strip has screws or spikes running in slotted holes, so the logs can drop while the wall stands still. Drywall is usually held short of the log ceiling or covered by a trim board that hides a gap.
• Screw jacks under posts. Posts that carry beams or a loft are often set on adjustable screw jacks, which an owner or builder backs off on a schedule as the walls around them settle. A post that does not get adjusted becomes a high point, and the floor or roof around it humps.
• Stair and cabinet attachments that let the log side move independently.

Running wire through logs

There is no wall cavity in a solid log wall, so wiring that needs to reach an outlet or switch on an exterior wall has only a few routes:

• Vertical chases drilled during construction, a channel bored down through the stacked logs from top plate to floor, usually beside a window or door where a switch was planned. If one exists it is the best route; the builder's plans or the original electrician may know where they are.
• Channels cut in the log behind a baseboard or in the top of the course where the next log hides them.
• Through the floor or ceiling into an interior partition, where conventional wiring methods work.
• Surface raceway, which is honest and serviceable, and which some owners refuse to look at.

Every box set into a log is a box that will move with the log, while the cable feeding it may be anchored above or below. Leave a service loop of slack at each box fed vertically, so settling takes up slack rather than pulling the cable out of its connector. Drilling or cutting into logs also means old finishes: an older log home may be coated in a preservative or stain containing compounds you would not want to breathe, so cut with dust extraction and a respirator under a written program per 29 CFR 1910.134 where the finish is unknown or old.

Running pipe and gas through and against logs

The rule for every piped system is the same: anything rigid that crosses from a part of the house that moves to a part that does not needs a joint that allows the movement.

• Drains and vents. A stack that runs from a basement slab up through a floor carried on log walls has a fixed bottom and a dropping middle. Install an expansion or slip fitting rated for drain-waste-vent use where the stack passes the moving floor, or support the stack from the moving structure so it rides down with it, and check the manufacturer's listed travel against the movement left.
• Supply lines. PEX with a loop of slack tolerates settling well. Rigid copper hard-strapped to a log above and a slab below will eventually pull a fitting.
• Gas piping. Gas piping must not be stressed by structural movement. Where a gas line crosses a settling wall or connects an appliance on a moving floor, use the routing and connectors the fuel gas code and the connector manufacturer allow, and sleeve it where it passes through logs. A gas line found pulled tight against a fitting is a leak waiting; treat it as such, check it with a leak detector solution or an electronic detector, and leave the gas off at that branch if it fails.
• Ducts and line sets. Ducts live in interior partitions and floor systems. A mini-split line set through an exterior log wall goes through a sleeve sized with room around it, sealed with a flexible sealant, not foamed solid.

Worked example: the upstairs tub drain that kept leaking

A four-year-old log home, two stories. The first-floor log walls are 9 feet tall from the slab to the second floor system, which bears on them. The builder's package lists a settling allowance of 3/8 inch per foot of log wall height for these kiln-dried logs, so the expected total is 9 times 3/8, which is 27/8 or about 3.4 inches.

The complaint. A leak at the ceiling below an upstairs tub. A plumber the year before re-made the tub drain's slip joint, and it leaked again within eight months.

The first repair was correct and still failed. The joint had been leaking, it was re-made properly, and it held. What nobody asked was why it had come apart.

The reading. With the ceiling opened, the tech traces the tub drain to the main stack. The stack is cast iron and PVC running from the basement slab up through the second floor, and it was clamped firmly to the floor framing at the second-floor penetration when the house was new. The floor system has been coming down with the walls; the stack is sitting on the slab and has not. The clamp has been dragging the floor's weight against the stack, and the stack has been pushing the tub drain fittings up relative to the tub, opening the joint.

How much has happened and how much is left. The gap above the front door measures only the logs beside the door buck, about 7 feet of wall, not the full 9. At 3/8 inch per foot those 7 feet should settle about 2.6 inches in total, and the gap behind the trim has closed by about 1.6 inches from the builder's original setting: 1.6 divided by 2.6 is roughly 60 percent spent at four years, which fits the expected early-heavy curve. Applying the same 60 percent to the full 9-foot wall, about 2.0 of its 3.4 inches has happened, leaving 3.4 minus 2.0, or about 1.4 inches, before seasonal swing.

The fix. The tech removes the rigid clamp, then splits the stack's support at a DWV-rated expansion fitting installed just below the second-floor connection. Below the fitting, the stack is supported from the slab and the basement framing as before. Above it, the section carrying the tub connection is supported from the second-floor framing, so it rides down with the floor and the tub instead of fighting them. The fitting is chosen with at least 2 inches of travel, covering the 1.4 inches left plus seasonal movement, and set near its extended position so that as the floor drops it telescopes closed rather than pulling apart. The tub drain joint is re-made with nothing now forcing it open.

What would have changed it. In a timber frame house with SIP walls and a floor carried on posts, the same leak would not point to settling, and the tech should look for an ordinary failed joint or a poorly supported trap. In a log home with no builder documents at all, the tech cannot estimate remaining movement and should pick the fitting with the most travel available and tell the owner the joint needs an annual look.

The failure mode prevented: a third re-made joint with the clamp still in place, and a fourth leak.

Sealing what you put through a log

Every hole you make in a log wall is a new path for air, water and insects, and logs move around it. Seal penetrations with a flexible, paintable sealant or a log-home chinking product that stays elastic, never with rigid mortar or a solid plug of expanding foam, which cracks or tears away as the log shrinks past it. On the weather side, slope the bore slightly downward to the outside so water runs out, not in, and put the penetration on a vertical face rather than the top of a log course, where water sits. Tell the owner where you penetrated, because log homes get periodic exterior re-staining and re-chinking, and the crew doing that work needs to know what is yours.

How to read a log home on the first visit

Five checks take ten minutes and tell you most of what you need:

1. Ask the age and the builder. A home in its first five years is still moving fast.
2. Look above every window and door for the settling gap. Closed or nearly closed gaps mean movement is outrunning the allowance.
3. Look at the top of interior partitions. Cracked drywall or trim pulled from the logs means a slip joint is jammed or was never built.
4. Find the posts. If they are on screw jacks, ask when they were last adjusted.
5. Look at every rigid connection between a log wall and anything else on your route, before you add yours.

References

• See related: Reading a House's Age from Clues on Site
• See related: Slab, Crawlspace and Basement Homes: What Changes
• The log home builder's or log supplier's documentation for that house, for its settling allowance
• International Fuel Gas Code in your adopted edition and the connector manufacturer's instructions, for gas piping exposed to movement
• 29 CFR 1910.134, for respirator use when cutting or drilling old log finishes