Log buildings range in size from a small trappers cabin up to very large lodge style structures. The size of your building should be determined by your needs rather than being limited by available log size. This article will discuss various basic cabin designs that will enable you to build cabins larger than your longest log length.
It is best if splices can be avoided. The splice is structurally weaker than a continuous log so splices need to be supported by the log below. The image below shows a lap splice with blocking to provide the needed support. The lap length should be 12-24 inches in length. Note that the blocks do not extend all the way out to the face. This way, the chinking will hide them. The joints should be bolted. The bolt holes should be countersunk and wooden dowel plugs installed to hide the bolts/nuts. Joints should be staggered at least 4 feet. It would also be good to drill vertical holes near the joint and drive a long rod or rebar through to strengthen the joint. Locating splices near intersecting walls can sometimes eliminate the need for blocking and rebar.
The pioneers knew a thing or two about log cabins. Although they probably wouldn't recognize the term "modular construction", many homesteaders used this approach to build their homes. Likely, upon arrival to their new land, the priority was to get a permanent shelter built as soon as possible. Later, as time permitted and the family grew larger, additions were constructed to enlarge the space.
A "pen" is a term used to describe four log walls arranged in a rectangle or square.
A pioneer might build a single pen cabin and later may enlarge it to a "dogtrot" or an "L".
Let's look at options available to a modern builder who has logs up to 16 feet long and who wants to avoid splicing logs...
Single Pen Single Story - The most basic building, 16' x 16'. With this cabin the builder would end up with less than 250 square feet of space (deducting for wall thickness).
Double Pen Single Story - The double pen cabin is actually two single pens separated by a space of 8-16 feet. A common roof is constructed over the both pens and the in-begtween space. For this example, let' say the builder used two 16x16 pens separated by 14 feet. The square footage for this building is about 720.
Some opted to leave the middle space open. This style is referred to as a "dogtrot". Most would probably want to enclose this area by adding two additional walls. These could be log or conventionally framed and sided with board and batten siding or lap siding. If logs are used, it may be a good idea to recess these walls by two feet or so to make it easier to connect to the two interior walls.
Double Pen Story and a half- With a steep roof pitch such as a 12:12, an additional floor can be built. To increase the usability of this loft area, many cabins were built as a "story and a half". To do this, a builder might construct the two pens 12 or 13 feet tall. With the upstairs floor at 8 feet, a 3 or 4 foot kneewall helps create more upstairs "walking space".
Even more space can be created by using additional pens. A third pen could be added to form an "L"
Keep in mind that the roof oultines above are generic. This article did not cover roof framing, dormers, porches, etc. Look for that information in a future article.