Log house
File:Arrowhead-log-homes.jpgA log home (or log house) is technically the same thing as a log cabin, a house typically made from logs that have not been milled into conventional lumber. The term log home is contemporary and preferred by most log home builders, while log cabin indicates a smaller, more rustic, log house, such as a hunting cabin in the woods.
Components
There are two kinds of log homes: "handcrafted" and "milled" (also called "machine-profiled"), made with a log house moulder. A handcrafted log home is typically made of logs that have been peeled but are otherwise essentially unchanged from their original natural appearance when they were trees. A milled or machine-profiled log home is one constructed of logs that have run through a manufacturing process to remove natural features and imperfections of the log and convert them into timbers that are consistent in size and appearance. Many handcrafted log builders do not consider milled logs a log at all, a position milled-log manufacturers disagree with.
Handcrafted log homes have been built for centuries in Scandinavia, Russia and Eastern Europe. The Scandinavian settlers of New Sweden brought the craft to North America in the early 1700s, where it was quickly adopted by other colonists and Native Americans. In the 1920s, the first milled log houses appeared on the market, using logs that were precut and shaped, rather than hand-hewn. Most log homes today are of milled variety mostly because they require less labor intensive field work and there are many more options available than with handcrafted alone.
Any timber from large to small will have moisture in it when it is fresh cut. Log homes of all types experience varying degrees of moisture content. In the case of "handcrafted" logs this moisture will naturally leave the timber, drying it out until it stabilizes with the climate it is in. This drying out causes movement and adjustment in the timber. As the wood dries the individual cells on the exterior of the crafted log will seal up. The remaining moisture in the center of the timber keeps trying to escape and will eventually open a crack in the crafted log. This crack, also known as a "check," can continue to the heart of the timber, sometimes leaving a large crack on the side of a home. This occurs in all log homes, regardless of construction method or how the timbers are allowed to dry and is considered normal as well as part of the charm of owning a log home.
Milled logs are processed in a different manner than Handcrafted logs. Logs destined to become Milled logs can become one of several types depending on the desired quality and end result.
- Green Timber*
Logs that are cut from the forest, brought to a mill and profiled are usually referred to as "green" logs. These logs will have a higher moisture content, sometimes upward of 25%. After construction, the timbers are allowed to dry in place.
- Air Dried Timber*
Some mills elect to let the fresh cut timbers sit outside in the open air to dry naturally. This process allows the moisture content of the logs to naturally come down as the timber dries. This process can take several months and requires the mill to have space to let the timber air out. Once the logs have dried for the desired time frame the logs are profiled and shipped to a customer. Profiling usually does not take place until right before shipment to ensure that the logs stay as uniform as possible.
- Kiln Dried Timber*
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 the logs. They can suffer severe checking and cracking if the kiln controls are not properly monitored during the drying process. Kiln Drying can cut down the dry time required by the manufacturer in order for production, from many months to a number of weeks, and usually results in an average moisture content of 18-20%, average being the mean moisture content of the outside of the log and the center of the log.
- Glue Laminated Timber*
"Laminated" or "Engineered" logs are a quite different approach to log home building. Full trees are brought to a mill equipped with a dry kiln, the bark is removed and the trees are sawn into boards usually no thicker 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 even 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 surfacer or planer which makes the face of the lumber perfectly smooth. These planks travel to a machine which then spreads a 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 to cure the glue in a matter of minutes and the other uses a high pressure clamp which holds the newly reassembled timbers under pressure for 24 hours. Once the glue has dried the end result is what is called a "log cant" that is slightly larger than the buyers 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 quite small timbers by using a combination of face and edge gluing as well as a process known as finger jointing. These boards which would be scrap to any other mill could be used in the center of a laminated log or beam to bring waste to a minimum.
Methods of Log Home construction
- Scandinavian Full-Scribe (also known as the "chinkless" method) where logs are scribed, custom fitted to one another, and notched where they overlap at the corners
- Flat-on-flat (logs are flattened on top and bottom and stacked)
- Milled log homes often are constructed with a Tongue and Groove system that helps to align one log to another as well as create a system for sealing out the elements.
- Tight-pinned butt and pass method where logs are not notched or milled in any way, logs in a single course do not overlap, and vertical pairs of logs are fastened with tight, load-bearing, steel pins.
Corner Styles
- Butt-and-Pass where unscribed or milled logs butt up against each other at the corners without notching
- Interlocking Saddle Notch - Normally seen on "D" or Full Round Profiles where a notch is cut into the top of one log and bottom of another, these two logs then interlock creating a tightly sealed corner.
- Dovetail - Typically seen on square or chink style logs. A special dovetail is cut on the end of a log where it would rest in the corner. One to the right, and one to the left. This also creates a nice tight interlocking corner.
- Saddle Notch - Typically used where two round logs overlap each other near the corners. It is common with the swedish cope profile.
Other Methods
- Half-Log where the structure is built with conventional (non-log) techniques. Half-log siding is applied to the exterior to replicate the look of full-log construction, it can also be seen with false corners to give a more realistic appearance..
Structural Types of Log Homes
From a structural perspective there are two fundamentally different types of log homes. In the most common type, the load forces of the building are transmitted to the foundation through the wooden logs. In the second type, the load forces are transmitted to the foundation through steel columns. These two types will be referred to as "Chinkless" and "Tight-pinned" respectively.
- Chinkless homes may have some chinking or sealant between the log courses, but the logs are typically milled or scribed to fit closely enough together so as to minimize the chinking requirement. Since the logs bear the weight of the building, any shrinkage of the logs is cumulative and the shrinkage results in the settling of the building, that is, the vertical dimensions of the building shrink as the logs shrink.
- Tight-pinned homes typically are built with unmilled logs, and as a result, there are large gaps between the log courses which must be filled with some kind of chinking material. The log courses are fastened to each other in pairs by steel pins which are driven through the logs. These pins are tight enough, and spaced closely enough (typically every 20 inches), so that they bear the entire weight of the building. The pins are typically 1/2 inch in diameter and are commonly made of rebar. When the logs shrink, each one shrinks around its own center line with the center line remaining fixed in its position in the building. As a result, the geometry and the dimensions of the building are unaffected, but the gaps between the log courses widen. Typically, the logs end up not touching each other so they play no part in the transmission of load forces. The logs do, however, prevent the pins from buckling under the load for the portion of the pin inside the log. The portion of the pin in the gap between the logs is a short column and thus is able to withstand the load without buckling.
- Advantages of the Chinkless method:
. Once fabricated and assembled, the shell of the log home can be disassembled and the parts shipped to the final building site. This allows for centralized manufacturing of the home and relatively quick construction at the final site.
- Disadvantages of the Chinkless method:
. Special consideration must be given for the settling of the building. This includes such things as slip joints over all the window and door openings, jacks under any vertical element 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.
- Advantages of the Tight-Pinned method:
. No allowance for shrinkage need be considered or made, thus simplifying design, construction, and maintenance.
. The building is stronger than the Chinkless buildings.
- Disadvantages of the Tight-Pinned method:
. The building must be fabricated and assembled on the final building site.
. Chinking maintenance is higher than for the Chinkless buildings during the period of major log shrinkage. That period may be several years for green logs.
Typically, the Chinkless method is preferred by log home manufacturers and the Tight-Pinned method is preferred by many do-it-yourselfers who build their own homes. Individual log home builders who do the work on the building site will find either method suitable for their purposes.
Types of Milled Logs
Milled Log Homes have an assortment of profiles that are usually picked by the end customer. Just about every profiled log on the market today features an integral tongue and groove milled into the top and bottom of the log that aids in stacking as well as eliminates the need for chinking.
- 'D' Shape Logs which are round in the outside and flat inside.
- Full round Logs which are fully round on the inside and out.
- Square Logs which are flat on both the inside and out and may be milled with a groove that could be chinked. When dealing with milled logs chinking is more of a personal preference and is not required to seal the home; however, A log home will eventually leak if it is not properly sealed.
- Swedish Cope logs which are round on the inside and out and include a half-moon shaped groove that is removed from the bottom.
Fastening Systems
These are some methods for connecting the logs together keep in mind each manufacturer usually recommends their own way of sealing and securing their logs.
Spikes: Basically a large nail, usually spiral, driven into the logs nailing them together.
Lag Bolts or lag screws: This system uses a large threaded screw to fasten the individual logs together.
Through Bolts: This method uses a continuous bolt from the foundation to the top course of logs. A spring may be used at the top to maintain downward force holding the logs securely in place.