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Log Homes - Wood Species
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All About Logs
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| Choosing the Right Wood for Your Log Home
Lodgepole Pine, Engeman Spruce, Douglas Fir and Western Red Cedar Log Homes A discussion of the different species The decision in choosing the species of wood you would like your home built from, is often as difficult as choosing the right log home company to build your home. Each log home company will generally have a "preferred" species of building log. The preference can be based on a long term knowledge of the characteristics of one individual species, or due to the lack of availability of a wider variety of species in their particular location. If a species is requested by a customer for a building log, the company then has to have the wood shipped into their log yard, adding further costs to the log package. Preference can also be attributed to the lack of quality of a given species in certain regions as well. This can be confusing for customers, as each company does tend to have very strong opinions on what wood should be used in building their home. In the long run, it is your preference that counts. Each species does have both pros and cons, and a general understanding of wood characteristics is beneficial in selecting the wood species for your own log home. Several characteristics to consider are appearance, resistancy to decay and insect, thermal qualities, workability, finish, as well as cost. Another important factor is the variance in color of heartwood and sapwood in the species available. At Falcon Log Homes Ltd. we offer Engleman Spruce, Douglas Fir, Western Red Cedar and Lodge-Pole Pine from British Columbia Canada. "British Columbia and its vast renewable, temperate rain forest and interior forests, produce arguably the finest trees in the world for use in log homes" The five major species that are indigenous to B.C. are Yellow Cedar, Western Red Cedar, Spruce, Douglas Fir and Pine. We do not offer Yellow Cedar due to its low availability and extremely high price. Western Red Cedar Log Homes: Western Red Cedar is one of the most sought after wood and is widely used for log homes. The heartwood is medium to dark coffee brown in color, with sapwood that is nearly white. The Western Red Cedar is slow growing, and as it is composed primarily of heartwood, has a high concentration level of both natural fungi and insect repellent toxins. It's bug resistancy makes this species preferably for export, especially to tropical climates. The grain is tight, but it is a softer wood. Western Red Cedar is one of the most expensive building logs on the market today. -High resistancy to decay and damage Douglas Fir Douglas Fir is commonly used for log homes, with only the second growth Fir being used for building logs. The second growth can be anywhere from 80-120 years old. Douglas Fir consists of a harder bark, which results in less marking during logging, as opposed to Western Red Cedar. Strong and beautiful, Douglas Fir can be noted as being one of the largest timber trees available and is valued as a great structural material as well as building material. -Most commonly used Engleman Spruce Engleman Spruce is the species I recommend when asked by our customers, as the quality of Spruce is very high and offered at a reasonable price, less expensive than both Western Red Cedar and Douglas Fir. Engleman Spruce is fine grained, very light in color, with minimal taper. As with Douglas Fir, it is available in very large diameters. A very important factor to consider is that Engleman Spruce does have a resistancy to heartwood decay, although in a somewhat lesser degree than Western Red Cedar, but more than Pine or Douglas Fir. -Light in color Any species that do not contain natural toxins should be properly protected with wood preservatives.
Wood Shrinkage and Moisture Content All log homes will shift and settle, regardless of the species of wood chosen, or the construction methods used. Without proper construction, settling in a log home can cause problems as logs shrink as they dry out. Log walls are also subject to compression from the weight of the logs placed above it. This is another key factor in choosing not necessarily the least expensive log home company to build your home, but rather one that produces the highest quality of log work. A good log home builder is aware of the wood shrinkage that will occur and takes this process into account in the designing and building of their homes. An experienced builder has the ability and knowledge to calculate the amount of shrinkage that will occur in a log, and by using proven techniques, compensate for any future shrinkage that the log will undergo. As handcrafters work with much larger diameter logs in longer lengths, than manufactured log homes, kiln drying is not generally an option. Rather than fighting the shrinkage, a good handcrafter must have an excellent understanding of the dynamics of a given species of wood in order to accurately anticipate shrinkage that will occur, and compensate for the settling that will likewise occur. Many manufactured log home companies are beginning to employ many similar techniques in their method of construction, due to the success of the handcrafted method of building. The method of construction of a log home must take into account the moisture content or levels of the wood to be used. Drying the Logs The shrinkage that occurs in a log home is greatly affected by the amount of moisture that is contained in the log. The moisture content of a live tree when harvested typically ranges from 50% to 100%. The moisture content of wood is measured by pounds of water vs. pounds of wood. Moisture level is directly dependent upon the species of tree, the season the wood is harvested, as well as the moisture content present in the soil content for the development of the root system during the tree's growing season. As previously mentioned, handcrafters primarily use " air-dried" house logs in their construction. It is imperative that the handcrafted log home company of your choosing, have some knowledge in the moisture content of the logs that will be used to build your home. It is in this area that we feel the handcrafted log home industry should employ consistant monitoring of the wood that is brought into their log yards. The term "dry" wood refers to a given species of a woods fiber-saturation point, generally referring to a 25%-28% moisture content. Air drying decreased the moisture content even further. Air Drying Air dried logs are stored in the builders construction yard or the decking yard of the logging company for a period of 6 months to 2 years, depending upon the climate where the log yard is located, and the species being used. The wood normally has a 15% -20% Equilibrium Moisture Content (EMC) in most areas. Moisture content can be measured through the use of a moisture meter, which is inserted 1/2" to 1" at right angles into the trunk of a tree. Determining the moisture content of a log is more difficult, and requires more exacting research. The lower the moisture content of the house log, the drier and lighter the wood will be. The Energy Efficiency of Log Homes Log homes are energy efficient. The thermal mass capacity of log walls are higher than those of brick or concrete walls of the same thickness. Logs have the ability to store heat, and then relinquish the heat when it becomes cooler inside. Consequently the overall energy efficiency of a log home is better than comparable structures. The Nation's Model Energy Code now recognizes the energy conservation benefits of thermal mass, which has been a victory for the Log Homes Council (LHC). The LHC has been claiming for years that a log wall's thermal mass does make a log home as energy efficient as a well-insulated frame wall. This claim was not officially acknowledged prior, due to the difficulty in quantifying thermal mass. Log home owners had the home heating bills to verify these claims, but the Department of Energy and Code officials required more than empirical evidence. In direct response, the LHC has gathered scientific statistics from independent research projects to substantiate its assertion. At the heart of the debate were the R-values, or the measure of heat transfer through materials. R-value measures a material's resistance to the transfer of heat from one side to another. Log walls have the ability to absorb and store heat in their cellular structure. The following is an excerpt from the LHC "Thermal mass is a material's capacity to absorb, store and slowly release heat over time. Logs do this well. The LHC set out to prove two things. First, logs have thermal mass because of their cellular structure, bulk and thickness. Second, this thermal mass provides significant energy-saving benefits because it released heat back into the house when temperatures drop. Early studies proved thermal mass properties significantly reduce heating and cooling loads in moderate climates. The National Institute of Standards conducted the most important of these studies for HUD in 1981-1982. However, energy experts continued to question the value of thermal mass during the winter months in northern climates. They doubted its benefit when heat is needed constantly and thermostat settings are opposite outdoor temperature. Two recent studies, both conducted in cold climate states, answer this question to the log home industry's benefit. In 1990, an independent testing agency, Advanced Certified Thermography, conducted a study for the Energy Division of the Minnesota Department of Public Service. It focused on heat loss through air leakage, assumed to be a problem with log walls because of their many joints. The study found the industry has substantially reduced air infiltration rates in the past 15 years. It credited this reduction to improve joint construction and the use of expanded foam sealants and gaskets on all joins and corner intersections. Leakage in the 23 test homes occurred where it in the same places it does in frame houses: at the peak of the cathedral ceilings, around window and door frames and along the tops of walls. The study concludes that air leakage in well-built, modern log homes is not due to their log walls. NAHB's research Center conducted the second study for the LHC in 1991. It showed the thermal mass of log walls does significantly reduce energy use for heating in cold climates. it based its conclusion on a comparison of the actual energy use of eight log homes to the actual energy use of eight well-insulated frame houses during one winter. The number of houses were evenly divided between upstate New York and Montana. The study also compared the homes actual energy use to their predicted energy consumption. The results led to the conclusion that log homes were as energy efficient as the frame houses. "What is significant here is the log walls' average R-values was 44% lower than the frame walls" average R-Value." says Carter. "Clearly we must conclude the thermal mass performance of log walls is an advantage to log home owners." An American study has shown that logs have a thermal performance value of R-22 for a building with 10" diameter logs with no insulation added. The logs used in our homes have a 12"-14" mean diameter, and with the addition of insulation being placed between the logs in the lateral grooves and notches add an even greater energy efficiency.
Fire Resistancy of Log Homes There is a recognizeable growth in the number of log homes, resorts and other buildings being built from log. One frequently asked question is "how do log walls perform in a fire" with the key question being "how long will log construction be able to withstand a fire until the manpower, equipment, and water can be deployed to extinguish it?" Acceptance by code officials of solid wood walls has been elusive in the past years, in regards to their capacity to be fire-resistive construction. "The Log Homes Council (LHC) and its Members have used various resources that relate the performance of solid wood walls to fire endurance. Some performed in-house tests while others tested their products in certified labs followed by specific standard procedures. And as the years pass, the number of fire survival stories continues to increase." The LHC maintains the position that a 4" log wall can achieve a 1-hr fire-resistive rating, with even longer ratings provided by the solid wood wall. A nominal 6" log wall achieved a 1-1/2 hr fire-rating in full scale testing. "As the log wall thickness increases, so does the fire rating" It is important to mention that handcrafted log homes use a much larger diameter log than those involved in the testing, further increasing log mass and wall thickness. "As an organic material, wood is combustible. Yet its insulation and charring characteristics produce an astounding response to fire. The charring effects of wood results in a protective coating over the surface of the material. This protective char coat is very similar to the effect created by some fire-retardant chemicals used to protect materials and assemblies." According to Barbara Martin, Log Homes Council's Executive Director, "it does take a long time for a log to burn to the point where they lose their load-carrying capacity." The information provided above is quoted from: A Test on the Fire Resistance of Log Walls The following test is quoted from: Log Building News "The Technical University of Zvolen, Slovakia, has commenced research to answer questions of fire resistance of a chinkless log wall used primarily in North America, and to develop a model for estimating the fire resistance of log walls. The large scale experiment according to ISO 834 was undertaken in PAVUS-Fire Research Institute, Czech Republic.
Experiment The test sample consisted of twelve spruce logs of 257 mm (10") average diameter. They were joined in the traditional chinkless, full-scribe fit style. The cupped lateral grooves were approx. 15mm (3/4") deeper than necessary, to accomodate the mineral wool insulation. The test wall was 3250 mm (10'-8") long, and 2800 mm (9'-2") tall. Eleven logs were kiln-dried to an average moisture content (MC) of about 19% and one log was conditioned to 36%. The long grooves were filled with mineral wool (rock-wool type). due to the natural irregularities of each log, the width of the grooves varied between 89mm and 130mm with an average of 105mm (4"). The ends of the panel were splined (like a door opening) and 3 spruce pegs per log, 30 mm in diameter, were driven approximately 800 mm (30") apart to support the wall logs. They were driven only through two vertically-adjacent logs. The log wall was exposed to fire, and temperatures inside the log, inside the grooves, and on the unexposed side were continually monitered and recorded. The log wall was continuously vertically loaded on the centerline with 15kN m(-1) using a hydraulic loading system built in the furnace loading frame. The load figure derived from the calculation of a one-and-a half story log house. The Results According to ISO 834, structural walls can fail in three ways during a fire resistance test: 1. fail in integrity, causing ignition of a cotton pad, permitting the penetration of flames resulting in sustained flaming, or 2. fail in insulation, causing an increase of the average temperature above the initial average temperature by more than 140 degree Celcius, or increase above the initial temperature at any location by more than 180 degress Celcius, or 3. fail in load bearing capacity Inside the furnace, the log wall surface turned black in the 3rd minute of the test. In the 5th minute the surface ignited and continued to burn for the duration of the test. Large deep cracks developed around the 11th minute. From about the 30th minute the walls surface was red and charred with large deep cracks for the rest of the test. It was observed that when the fire-exposed edge of the lateral groove burned off, the mineral insulation inside the long groove protruded, and expanded to about its inital thickness of 50mm. No flame penetration through the wall was observed during the test. The side unexposed to fire showed no visible changes, smoke penetration was not observed through the wall joints. Comparing the results of chinkless log wall joint with the chinked wall joint tested by Sashco Sealants Inc., the scribe-fit log wall has a much higher insulation value. At 60 minutes of the test duration, the chinkless log wall showed absolutely no increase in surface temperature, compared to an average 71 degrees Celsius temperature increase of the chinked log wall tested by Sashco Sealants Inc. The temperature on the hot side of the scribe-fit log wall exceeded 1100 degrees Celsius, but the cool side never got above 48 degrees Celsius, even after almost 3 hours of burning. Conclusions Knowing how log walls react to fire exposure is important for evaluating newly constructed buildings and existing log structures. A large-scale laboratory test showed that a massive wooden wall with considerable numbers of lateral wood-to-wood joints can maintain the fire safety requirements prescribed by the ISO 834 for as long as 172 minutes. The log wall withstood 180 minutes from its integrity and insulation viewpoint and 172 minutes from the point of its load bearing capacity. The handcrafted chinkless log wall constructed in the manned described above shows better integrity, insulatiion, and load bearing capacity than the chinked or milled log walls tested by other laboratories and detailed in this article - its properties provide significant resistance. Log Homes and National Disasters
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