Log Home Construction
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The Non-Traditional structure that I chose to design is a log home. When doing research on styles of construction I was a little overwhelmed with the options that are available for construction methods. The first thing I needed to find out is what type of footing and foundation is needed to support the immense weight of the logs. An 8″x16″ footing and 8″ foundation is sufficient enough to support the weight of a log home. There are three different options available for supporting the floor joist in a log home. The first is setting the joist directly on top of the mud sill plate. Rim joist or ribbon joist is required at the ends of the joist to cover the ends of the joist. The second option is making a 4″ deep notch every 16″ or 19.2″ (depending on joist span and loading) in the 8″ foundation to place the joist into. The depth of the notch depends on joist depth but the notch should be deep enough for the top of the joist to match the top of the mudsill. This style doesnt require rim board because the ends of the joist are already covered up. The third option is to hang the joist from the mudsill using top flange joist hangers. This option also doesnt require rim board because the ends of the joists are already covered up. Typical Ñ*” tongue and groove sub flooring is fastened on top of the joist.
There are two different styles of log home construction. The first is manufactured log homes also known as kit homes. The logs are mechanically shaped into uniform dimensions. Manufactured logs may also be milled round or rectangular in profile with endless variations. The second type of construction is handcrafted. The natural characteristics of the logs are preserved to show off their individuality and the joinery of the logs is done with hand held tools. There are three different styles of logs. The first is a D shape log for the exterior log look and flat indoor appearance. The second is fully rounded logs to give the full log look on both the interior and exterior. The third is a square log that gives the appearance of timber construction, being flat on all four sides, with the advantages of log building. Depending on the manufacturer and your corner type, milled logs also come with tongue and grooves on the top and bottom of the logs for a more secure fit. This is common on the “D” and the square log. Rounded logs either stay round or are coped, also known as a Swedish Cope, Scandinavian Scribe, or Double Scribe. Swedish Cope cut logs are shaped in a concave shape of the adjacent log, allowing for the tightest fit from one log into another.
Corner notching is another of the characteristic features of log construction. Most notching methods provide structural integrity, by locking the log ends in place, and give the structure rigidity and stability. Corner construction is very important because it determines what the look of your log home will be. There are three common styles of corner construction. The first is Butt-and-Pass, where unscribed or milled logs butt up against each other at the corners without notching. The second is the 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. The last is 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 that sheds water.
Fastening the logs together is also very important. There are 6 different methods for connecting the logs together, keep in mind each manufacturer usually recommends their own way of securing their logs. The first option is Log Spikes: They are basically a large nail, usually spiral, driven halfway into each log, securing them together. The second option is to use Lag Bolts or Lag Screws: A large threaded screw fastenens the individual logs together. The third option is to use Through Bolts: Through bolts are a threaded rod that runs down through the entire wall system. The diameters of these bolts range from 1/2″ to 1-1/2″. Shorter lengths of bolt are typically joined with threaded couplings to achieve the required wall height. The very top of the bolt is often threaded so that a washer and nut can be tightened down over the bolt. These bolts are located near the ends of walls, at openings, and are commonly spaced from 4 to 8 feet on center. The fourth option is to use a Threaded Log Home Screw: These screws self-drill and countersink their head in order decrease installation time. The fifth option is Drift Pins: Used to resist lateral loads parallel to the axis of the log, the pins are galvanized pipe or rebar that are set in predrilled holes with a minimum of 5″ fixed into the log below. The sixth option is Wood Dowels: Dowels, usually of hardwood, may be used to hold corners, prevent twisting, or limit logs from shifting out of position as the logs are set.
Even though logs provide very efficient insulation qualities cracks and gaps still occur. Depending on the types of logs used and the type of corner used different methods of insulating are needed. Wool can be used in laterals and notches of log home construction for insulation purposes. Wool is an environmentally friendly substitute to other types of products available on the market, mainly fiberglass insulation. Wool traps tiny pockets of air allowing for its insulating abilities (R-Value of approximately 2.7 per inch). Wool isnt as much of an irritant as fiberglass insulation is. Wool also repels moisture as opposed to absorbing it. Wool is available in two different styles, ropes and batts. Chinking is also another option for insulating purposes. Any joint that is greater than 1/4″, a round, flexible length of polyethylene backer rod (looks like a rope of foam) is used to produce a surface backing for the chinking. It also insulates and saves on the amount of chinking material used, but essentially it acts as a bond breaker allowing the chinking to adhere only to the top and bottom of the logs, not to the backer rod. This allows the chinking to adjust instead of peeling away as the logs shrink. Chinking is an elastic sealant, like a synthetic mortar, and is used to seal the log joints. Chinking joint width should be a minimum of 1/4″, a maximum of 2″, and be 4 times the expected movement. Chinking joint depth should be 1/4″-1/2″.
As far as roof systems are concerned there are three options available. The first is a log purlin roof. This is where logs are supported on the gable ends and span the length of the home. For every two logs vertical on the gable end is one horizontal purlin, depending on the pitch of your roof, length of structure, and log thickness. Log rafters