By Jim Cooper of Log Homes Made Easy Online
Wood shrinkage and the resulting settlement and movement are not problems but characteristics of working with a natural material. Shrinkage only becomes a problem when the manufacturer, builder or home owner fails to recognize or respect it. I would much rather have a house made from logs with 30 or even 40 percent moisture content, that is designed and built with full recognition of that fact, than a house made from logs at 20 percent moisture content, designed and constructed in denial that any more shrinkage or settlement will take place.
How much shrinkage or settlement are we actually talking about? I certainly hope that no one expects a log home to drop down around their ears from settlement. While it is important and under certain conditions even critical, most settlement and shrinkage concerns are more for energy efficiency, maintenance time and expense and construction quality than for structural integrity. The basic engineering of a log home makes for a strong house that can withstand a great deal of design and construction abuse.
When I speak of settlement, I'm generally referring to a range of 1 to ,3 inches in an 8-foot wall. What does this mean to the home owner? Consider a rectangular log home 24-feet wide, with a shed porch on the front and a second-floor master bedroom. The logs surround the first floor, there is a cathedral ceiling over the great room, the gables are log, and the roof is framed with either conventional rafters or heavy timbers. There have been no provisions for settlement built into the home. Let's say the log walls enclosing it settle an inch.
Now the second floor, which started out level, is sloping from the center of the house toward the front and rear walls, at the rate of one inch in twelve feet or 1/12 inch per foot. In three feet, this works out to 1/4 inch. The master bedroom door, set in the framed wall crossing the house at the top of the stairs, is almost three feet wide. Originally the door had 1/8-inch clearance on all sides. Now the jamb closest to the log wall is 1/4 inch lower than the other, so the door won't close. The remedy? Plane the door top so it's no longer square and reset the strike plate so the door will latch, or remove and reset the door jamb so the door remains square in its opening, although the frame will no longer be square with the wall.
Over time, the home owner may notice difficulty opening a window. Eventually the window may cease to function entirely and may even crack. The cause: settlement causes the weight of the logs and roof system over the window opening to rest squarely on top of the window buck, or frame. Pressure on the frame distorts the opening, eventually interfering with the functioning of the unit. The same thing may occur at door openings in the log wall. The remedy: Reset the door window, shortening the door, if necessary, or replacing the window unit with smaller one.
These aren't major repairs and in the long run will probably cost no more to fix than the problems that can arise in a conventional home. If settlement is greater than half an inch, or the design of the house is more complex than a simple rectangle, problems and remedies may become more complex, costly and even risky.
I've talked with home owners who insisted their houses hadn't settled at all. However, they pointed out that gaps had appeared between their logs that required caulking. Their logs were shrinking, but their houses were not constructed to allow settlement as this shrinkage occurred. The result was spaces between logs. Had the houses included settlement provisions, the gaps would not have occurred.
So, what if you've been assured by a log home salesman that his company's house will settle less than 1/2 inch. Consider this: Depending on the height of the logs, a typical wall has 16 to 21 courses of logs laid horizontally--the direction that produces maximum vertical settlement. In addition, there are 16 to 21 horizontal joints in the wall, often containing foam seals, gaskets or caulks. If each log shrinks in cross section by 1/16 inch or if each joint compresses by that amount, the settlement in the log wall will exceed an inch. In other words, even though the average movement may be small, the overall movement can be significant.
The important consideration is actually how to handle settlement, not whether you can avoid it. Settlement is affected by the kind of wood, conditions under which the trees were grown, season when logs were cut, engineering system, construction methods and even the type of heating and cooling system used in the home. So there isn't a single simple answer. Engineering and building for settlement involves preparing for a range of possible movement.
Most log home companies include settlement spaces above doors and windows. This gap, filled with loose insulation, allows the logs to settle around the opening without putting pressure on top of the frame. For some manufacturers, that may be the only allowance made for settlement. My question to them is, "If you expect for the log wall to settle an inch at the window or door, where do expect that inch to go in the center of the house?" The answers are sometimes amusing. "We put the settlement space in as a precaution, actually you don't need it." Or, "There's enough flexibility for the interior framing to absorb it." The first answer is like saying, "We put seat belts in your car but we don't include buckles because our buyers don't have accidents." In the second case, I wonder when they last applied a few thousand pounds of pressure to the edge of a piece of drywall to see how well it was absorbed.
To accommodate settlement inside the house as well as in the log walls, there must be settlement space in interior framed walls. So-called "shrinking" or "settling" walls, used by a number of log home companies, place the weight of the second floor and roof on posts rather than bearing walls. Interior framed walls contain a space near the top that is concealed behind trim secured only to the top of this settlement space. The support posts rest on shims or adjustable jacks.
As the log walls settle, the shims are removed or the jacks are lowered. This lowers the center of the roof and second floor system, keeping it aligned with the log wall. As the center is lowered, the settling space, concealed behind trim, closes. Because the trim is fastened only at the top of the settling space, it isn't necessary to remove it to make an adjustment. As a bonus, since there are no interior bearing walls, the house is a remodeler's dream. You can knock out and rearrange walls to your heart's content. Just don't mess with those posts!
At this point, you're probably saying, "Whoa, you're telling me to lower my second floor and roof as my log walls settle? And this is simple? And easy?" Actually, yes. Just recently, I performed exactly this procedure on a house built almost two years ago. When we started, the second floor was 3/4 inch out of level and the door into a second-floor bedroom would not close. The adjustment required a wrench and took about an hour. (Actually it took longer because we made the adjustment in stages to minimize stress on the second-floor system.) When we left, the second floor was level again and the door worked perfectly. So the process is not difficult, time consuming or costly. But there are two big "ifs" attached. If the house is designed properly and if the builder followed the instructions and construction detail drawings provided by the manufacturer. Builders who understand the principles involved can usually build a fully adjustable log home without special drawings or instructions.
In addition to settling spaces in interior framing, it's important that the logs be allowed to settle. This means that framing attached to log walls is attached by nails or screws driven through a slot in the framing. As the logs settle the nails or screws simply slide down the slot. The same method is used to secure window and door framing to logs. If this is not done, logs will be prevented from settling and gaps will appear.
There are three areas of special concern in making a log home fully adjustable for settlement: log gables, stairways and fireplaces. Log gables settle unevenly because of their shape. Consider a log gable with 20 courses of logs at the peak, tapering to none at the edges. If the log wall settles 1 inch, the bottom of the rafters will sit 1 inch lower while the ridge of the house will actually lower 2 inches (1 inch in the log wall and another in the gable.) As this happens, stresses on the roof and gables will change, perhaps causing additional roof and gable maintenance such as resealing, flashing and re-setting trim. Log gables may be pretty, but they are expensive, difficult and prone to problems. It's much less expensive to frame gables and cover the exterior and interior with matching log siding or contrasting treatment. Many companies make log siding and tongue and groove especially for this purpose.
Stairways also present a challenge. Changing the distance between the first and second floors changes the rise of the stairs. Lowering the second floor an inch will result in the top riser of the stair being an inch shorter than the others, a violation of many building codes. Also, the top of the stair carriage will be an inch above the second-floor level after adjustment. The stair carriage should not be fastened to the second-floor system or to any framing above the settlement space in interior walls. If it is, it will prevent making adjustments for settling. There are several ways to accommodate stairs, but one of the simplest I learned from a skilled handcrafter. He simply sets the stair carriage on a slight pitch. The stairs start out with treads angled slightly forward and end sloping slightly back. A pitch of 1/16 inch across the tread will handle up to several inches of settlement adjustment and will not be noticeable.
Stair railings need to be securely fastened at both the top and bottom of the stairs. I've built railings secured at the top by screws concealed behind button plugs. When we make an adjustment, we pop off the plugs and remove the screws. After adjustment, we drill new holes, reinsert the screws and replace the plugs.
Chimneys also present challenges in accommodating settlement. The easiest solution calls for a chimney that is fully enclosed within the house and passes directly through the roof. In this situation, the chimney is completely free standing or anchored to roof framing by nails passing through nail slots. On the roof, flashing and counter flashing overlap enough to form an adjustable sleeve that continues to protect against water infiltration when the roof is lowered.
Chimneys along outside walls are more challenging. The chimney won't settle like the logs, so any attachment between the two must be flexible. Logs need to move past the chimney as the wall settles. If the logs aren't allowed to settle, gaps will develop, possibly resulting in air and water leaks around the chimney.
The way to deal with settlement in a log home is to recognize it as a characteristic rather than a problem. Look for adjustable design details and builders familiar with the process of settlement.
If a salesperson says, "My houses don't settle enough to require special treatment," ask to see at least half a dozen houses over five years old and talk with their owners. If you discover no problems, you can at least feel confident that any settlement that's taken place was probably not major.
Finally, if these sorts o adjustments make you apprehensive, consider one of the super-efficient log styles using half logs over framing or structural panels. Rare a few years ago, more than 40 log companies now offer this blend of log appearance with advanced engineering. In addition to high energy efficiency, this type of construction eliminates any need for settlement details in either exterior or interior framing.