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Log homes

Log homes

Log Cabin, a box-like dwelling made of small logs. The log cabins of the American pioneers were simple in construction because trees were their only building material, and the ax, adz, and auger were their only tools.

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The log cabin became a symbol of frontier life.

The typical log cabin was a small, one-room hut with one door and perhaps one or more small windows. The spaces between the logs were packed with mud to keep out the wind and cold. Because there were no nails the logs were fastened with notched ends, or with wooden pegs. The roof was made of overlapping rows of short boards. The floor was hard-packed clay. The window openings were covered with oiled paper to let in a little light. The room was heated by an open fireplace that also served as the cook stove.

Log cabins were used widely in Europe, especially in Germany, Switzerland, and the Scandinavian countries. Swedish settlers built log cabins when they came to Delaware in 1638. Other colonists followed their example. When great numbers of settlers began to move westward after the Revolution, they found thick forests in Tennessee, Kentucky, and the Northwest Territory, and the log cabin became the typical home of the backwoodsman.

The log cabin gained fame during the political campaign of 1840. Small log cabins were used in parades to show that William Henry Harrison had the support of the frontier people. Probably the world’s most famous log cabin is the one in which Abraham Lincoln was born. Many other Americans who rose to greatness spent their early years in log cabins.

Log house

Canadian -style log house

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American -style log house

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British Colombia -log house

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A log house (or log home) is structurally identical to a log cabin (a house typically made from logs that have not been milled into conventional lumber). The term “log cabin” is not preferred by most contemporary builders, as it generally refers to a smaller, more rustic log house such as a hunting cabin in the woods, or a summer cottage.

Log houses are especially popular in Sweden, Finland, Norway and Russia, where straight and tall coniferous trees, such as pine and spruce, are readily available. They are virtually unknown in Central Europe, where timber framing is favored instead.

There are two types of log house:

  • Handcrafted: Typically made of logs that have been peeled, but otherwise essentially unchanged from their original appearance as trees
  • Milled (also called machine-profiled), made with a log house moulder: Constructed of logs that have run through a manufacturing process which convert them into timbers which are consistent in size and appearance

Handcrafted log houses have been built for centuries in Scandinavia, Russia and Eastern Europe, and were typically built using only an axe and knife.The Scandinavian settlers of New Sweden brought the craft to North America in the early 18th century, where it was quickly adopted by other colonists and Native Americans. Possibly the oldest surviving log house in the United States is the C. A. Nothnagle Log House (circa 1640) in New Jersey.

During the 1920s the first milled log houses appeared on the market, using logs which were pre-cut and shaped rather than hand-hewn. Many log houses today are of the milled variety, mainly because they require less labor-intensive field work than handcrafted houses. There are about 500 companies in North America which build the handcrafted, scribe-fit type of log house.

Components

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Scribe-fit handcrafted logs

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The logs in log houses have a varying degree of moisture content; all logs have moisture when freshly cut. In the case of handcrafted logs moisture will naturally leave the timber, drying it out until it stabilizes with its climate. This drying-out causes movement and shrinking of the log’s diameter. As logs and timbers dry, the differential shrinkage (radial versus tangential) causes small cracks (known as “checks”) to open slowly over time. Checking is a natural process in both air- and kiln-dried logs. This occurs in all log houses regardless of construction method or how the timber is allowed to dry, and is considered normal.

Milled logs are processed in a different manner from handcrafted logs. Logs destined to become milled logs may become one of several types, depending on the desired quality and results.

Green logs

 Logs that are cut from the forest, brought to a mill or to a log-house construction yard, have their bark removed and are used to build a log-house shell (handcrafted log houses), or sent through profiling machines (manufactured logs) are usually referred to as “green” logs if they have not been air- or kiln-dried. “Green” does not refer to color, but to moisture content (MC).114

The actual moisture content of “green” logs varies considerably with tree species (cedar, fir, spruce, pine etc.), the season in which it was cut, and whether sapwood or heartwood is being measured. Green logs may have a moisture content ranging from about 20% to 90% (the oven-dry method of measuring MC).

One type of air-dried log is “dead standing,” which refers to trees which have died from natural causes (bug kill, virus, fire etc.) and cut down after they died. Standing dead trees may be cut one month or several decades after they died, so the term “dead standing” does not necessarily mean the logs have dried down to equilibrium moisture content. Dead standing logs can be green, or more-or-less dry.

After construction, green logs dry in service in the log building. Within about four years, green logs which are part of a completed log house reach equilibrium with local conditions and have equilibrium moisture content (EMC) of between 6% and 12%. The actual EMC varies with local climate, season and location.

Air-Dried Logs

Some log home companies let the fresh-cut logs (or milled timbers) sit outside in the open air to dry naturally. The timbers may be stacked with spacers (known as “stickers”) between them. This process allows the moisture content of the logs to naturally fall as the timber dries. In areas of high humidity, it may require as much as one year per inch of log thickness to dry. Arid climates may require less. A log with a diameter of 8 inches will usually reach equilibrium in about 18 months in the Rocky Mountains of North America. Air circulation is critical or the logs May begin to rot before properly drying, especially in humid

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regions. If the logs are to be dried to equilibrium with the local climate the process may take several years, depending on the location and size of the timbers. In some environments, the logs must be kept under some type of roof or cover to reduce the impact of rain storms on the drying process.

Once the logs have dried for the desired length of time, they are profiled prior to shipping. Profiling usually does not take place until shortly before shipment, to ensure that the logs stay as uniform as possible. It is uncertain whether this process is advantageous; it depends on many factors such as local climate, wood species, its size, and the location of the log structure.

Kiln-dried logs

Mills that have a kiln on site have the option of artificially accelerating the drying process. Green timber is placed inside a large oven, where heat removes moisture from them; however, they can suffer severe checking and cracking if the kiln controls are not properly monitored during the drying process. Use of a kiln can reduce the drying time from many months to several weeks. Kiln-drying usually results in an average moisture content of 18-20% (“average” means the average moisture content of the outside and the center of the log).

Milled-log types

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Since logs reach equilibrium moisture content at about 6% and 12% (in North America);[8] since most kiln-dried logs are dried down to about 18% to 20% moisture content kiln-dried logs can be expected to shrink and settle over time, but to a lesser extent than green logs. Common varieties of softwood lumber (such as framing lumber) are dried to somewhat higher moisture content.

Glue-laminated timber

“Laminated” or “engineered” logs are a different approach to log-house building. Full trees or (alternatively) sawn cants (unfinished logs to be further processed) are brought to a mill with a dry kiln, the bark is removed and the trees are sawn into boards usually no more than two inches thick. These boards are then taken to the dry kiln, where (because of their size) they can be dried without causing severe damage to the wood. Timber destined for glue lamination must be brought down below 15% moisture before the lamination process will work, so typically these timbers are dried to around 8-10% moisture. The drying process varies on the species

of lumber, but can be done in as little as a week. Once the drying process is complete the planks are sent through a surface (or planer), which makes the face of the lumber perfectly smooth. These planks travel to a machine, which then spreads special glue on the interior boards.

Depending on the type of glue and type of mill, there are two ways to finish the lamination process. One type of glue reacts with radio-frequency (RF) energy to cure the glue in minutes; the other uses a high-pressure clamp, which holds the newly-reassembled timbers under pressure for 24 hours. Once the glue has dried, the result is a “log cant” that is slightly larger than the buyer’s desired profile. These log cants are run through a profiler, and the end result is a log that is perfectly straight and uniform. Some mills are capable of joining together small timbers by using a combination of face and edge gluing and a process known as finger- jointing. Boards which would be scrap at another mill may be used in the center of a laminated log or beam to minimize waste.

Types of milled logs

Milled log homes employ a variety of profiles which are usually specified by the customer:

D-shape logs              Full-round logs          Square logs                            Swedish Cope logs

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D-shape logs: round on the outside and flat inside

Full-round logs: fully round inside and out

Square logs: flat inside and out, and may be milled with a groove which could be chinked. When dealing with milled logs, chinking is a personal preference and not required to seal a house; however, a log house will eventually leak if it is not properly sealed.

Swedish Cope logs: round inside and out, with a half-moon-shaped groove on the bottom

Nearly every profiled log on the market features an integral tongue and groove milled into the top and bottom of the log; this aids in stacking, and reduces the need for chinking. Wood is not airtight — caulking or chinking will improve energy efficiency.

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Construction methods

• Scandinavian Full-Scribe (also known as the “chink less method”) is naturally-shaped, smoothly-peeled (draw knifed) logs which are scribed and custom-fitted to one another. They are notched where they overlap at the corners, and there are several ways to notch the logs.

• In the flat-on-flat method, logs are flattened on the top and bottom and then stacked (usually with butt-and-pass corners).

• Milled log houses are constructed with a tongue-and-groove system which helps align one log to another and creates a system to seal out the elements.

• With the tight-pinned butt and pass method, the logs are not notched or milled in any way. They are in a single course and do not overlap; vertical pairs of logs are fastened with tight, load-bearing steel pins.

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An Umgebinde house in far-eastern Germany

Settling

Once fabricated and assembled, the shell of the log house may be disassembled and the parts shipped to the building site. This allows for centralized manufacturing of the house, and relatively quick construction on site. Full-scribe-fit handcrafted log construction is a method of precisely marking where to cut each individual wall log to provide a tight fit between naturally-shaped logs along their entire length and in the corners. A high degree of craftsmanship is required for success in this method, and the resulting tight fit of naturally-shaped logs has aesthetic appeal.

Log houses which settle require slip joints over all window and door openings, adjustable jacks under vertical elements (such as columns and staircases) which must periodically be adjusted as the building settles, allowances in plumbing, wiring, and ducting runs, and fasteners for the walls themselves to prevent uplift.

References