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 several 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 its effects and will build to compensate for shrinkage and settling. The Log Building Standards 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 its 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 planning 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 many 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.