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Wood Species and Characteristics
as written in the ILBA Land to Lock up Manual
The log home: by definition, logs are
the single most predominant characteristic of these log homes,
and the very reason builders and owners alike, are drawn to
this form of construction. What could be more natural? The
appeal of logs is apparent to all log homebuilders and owners.
Visitors to log structures are immediately drawn to touch
the logs, soothed by their strength and character. (How
often do you see people caress drywall?)
 The
longevity and strength of logs is evidenced in the well-built
log structures of Norway and Russia, which are still standing
proud and true after more than 800 years. The integrity of
the structural design is essential to a long-lived legacy,
and a careful look at structural components is critical. The
choice of what logs to use is also an important consideration,
and it is worth understanding the differences and characteristics
of various species.
Different building styles can dictate what types
of logs are used. Handcrafted log homebuilders select logs
based on an extensive list of characteristics. Different species
may be superior for certain joinery techniques, building design,
and structural performance. Geographic location (where the
logs are going to, or where they are coming from) might also
be a consideration in wood selection. Weight bearing logs
such as wall logs, floor joists, roof rafters, purlins and
truss components usually require engineering and some species
are better suited for these structural requirements.
The log builder, presented with the task of
selecting appropriate wood for a project, needs to consider
what lengths are required, what the average mid-span diameter
is, what is the amount of taper the logs have and what maximum
butt size and minimum top size are acceptable.
Midspan size of log diameter will contribute
to the thermal performance; the larger the log, the greater
the “R” value attributed to it, based on formulations
attributed to various species of wood. Depending on climatic
requirements and local building regulations, a minimum log
diameter will be required. Based on an average R 1.5 per inch
of log diameter, coupled with the extent and integrity of
joinery between the log surfaces, a minimum 10” log
is an acceptable norm for log diameters. Once might, however,
use logs of smaller diameter if the purpose of the building
is, for example, a summer cottage.
No matter how dry the logs are, all log structures
must be built to accommodate shrinkage and settling. Whether
building with seasoned wood, standing dead, green, winter
cut, or kiln dried, a knowledgeable log builder builds according
to moisture content, anticipation and allowing for movement
in response to the drying and seasoning process with allocations
for shrinkage and settling of logs. As wood fibre loses moisture,
cell walls shrink and collapse, which can reduce the overall
diameter of a log by as much as 6%. This factor, accumulated
over the finished height of a log wall, as well as through
door and window openings and structural support points, must
be accommodated.
Moisture gain and loss can also be affected
by roof overhangs, proper elevation from grade, and treatment
to the wood surfaces with effective stains and preservatives.
Controlling moisture content of the logs is important. A surface
stain or preservative must allow the logs to breath and expel
excess moisture, otherwise an environment for rot and decay
is created. In some very arid areas, humidity should be introduced
into a log home in order to stabilize wood fibres and to slow
down the drying process and avoid radical checking.
In cold climates, logs react differently during
the seasonal changes. Warm interior log walls may dry out
while the outside surfaces remain frozen and do not continue
losing moisture until the hot summer sun beats down. Unless
the log building is constructed from kiln dried logs, this
see-saw process of moisture balancing can continue for a number
of years before the wood stabilizes.
Most handcrafted log builders prefer to work
with green wood, preferably winter-cut (when the sap is still
down in the roots). Green logs are more easily crafted and
a skilled builder will calculate moisture loss and it’s
effects and will build to compensate for shrinkage and settling.
The Log
Building Standards (675Kb PDF) describe many of the techniques
that are used to accommodate settling.
Since seasoned fire-killed, kiln-dried, or dead-standing
timber is harder to work with it is often preferred for use
in chinked log wall structures where less work is required
on the laterals. Dead standing and kiln-dried wood can also
be used in full scribe work. While “dry” wood
does settle less it will also lose moisture and the log builder
must anticipate and build accordingly.
“A rose by any other name is still a rose.”
One of the greatest discussions between builders, and perhaps,
one of the questions we are most frequently asked by our clients;
is what species of wood should be used. Cost plays a role
in choosing wood species, but it is not the most important
factor, since all species have their own desirable traits.
Geographic location and forest ecosystem bear
the greatest influence on log selection. Primarily softwoods
are chosen due to their superior “R” factor, ease
of handling, straightness of grain, and availability. Cedars,
Pine, Spruce, Fir, and Larch are all commonly used as building
logs, and each has different qualities. Western Red Cedar
contains turpentine’s within its resins thus rendering
it more rot resistant, and it does not check or shrink as
drastically as other species. Douglas Fir is heralded for
its superior density, if it lacks in simple “R”
value, it is made up for in structural performance. Spruce
is valued for it’s light colour, and while it may not
match the qualities of Douglas Fir for structural loading,
it is none the less an excellent choice of building log.
Access to these species, coupled with harvesting,
handling, and government tariffs influence the price of building
logs. Building with Eastern White Pine may not prove practical
in Alberta, British Columbia, or Washington. The best logs
to use are often what is most readily available to the builder.
The consumer is then faced with the choice of either accepting
the local species, or making arrangements with their builder
to purchase another species.
Aesthetic considerations also matter; contrasting
heartwood and sapwood in various trees have different looks
– the absence or presence of burls, cat face, fire scars
and other distinguishing features may want to be included
or avoided.
Regardless of species and its characteristics,
the log builder scrutinizes every log. He considers direction
of grain, presence of windshake, decay, insect infestation,
mechanical handling scars, and culls logs that have too may
limbs and knots. History has shown us that all wood species
can be used within certain parameters.
Logs are a renewable resource. Wise and selective
use of our trees and our forestry practices must be seriously
re-evaluated. Clear-cut practices, reforestation, and selective
logging are all influencing what logs are available. The log
builder can make efficient use of our forest heritage. With
a keen eye on criteria necessary to produce fine log buildings,
we create structures that will survive for centuries, each
reflecting the spirit of the forests it came from. Building
with logs makes sense. What we build with and how we ensure
its most efficient and effective use becomes a priority for
both the builder and the buyer.
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