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Making Allowances for Settlement
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| By Jim Cooper
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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. |
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