Like all trades, there is a lexicon associated with log building used to describe some of the specific processes, tools and techniques that we employ on a daily basis. And there are some great words, confusing words and words that mean something different in log building to other uses you may be more familiar with. We’ve compiled a list of some of our favourite log building words to help you understand the difference between caulking and chinking, what scribing is, why a ‘fluting’ might not be a bad thing and why a sleeper log is actually a really active part of the cabin!
Cap log
Also known as a plate log or wall plate, a cap log is the uppermost horizontal log of a wall which provides the fixing point for the feet of the rafters. This load-bearing structural log distributes the weight of the roof evenly across the width of the wall without generating pressure points.
Caulking
Similar to chinking (below), caulking is used to fill smaller gaps (typically less than one inch) between logs and its more elastic properties allow it to shrink as the logs dry out and settle. Caulks typically have no texture and are therefore used to give a smooth finish to those smaller gaps.
Chinking
Chinking is a filler used to seal larger seams between rows of logs. It can be used both internally and externally and typically comes in a range of colours and textures which allow it a decorative as well as functional role in the weather-proofing of a cabin. Certain textures may even give the appearance of mortar, which of course it isn’t.
Corbel
A corbel is a short structural log that projects out from a support point such as a wall or a post as a load-bearing element, reducing the span of a structural beam above. Predominantly used to support extended roof spans or cantilevered balconies they can also be an aesthetic feature.
Fluting
The beautiful aesthetic created by the lower part of a tree trunk where long recesses form in the growth of the tree toward the base. In the log building world, this is most apparent in Western Red Cedar but can be found in many species. In section these flutes create a unique and decorative effect to the log ends used in a build. Fluting also refers to a process creating a similar look in the carving of stone pillars.
Green wood
As you probably already know, green wood is freshly cut timber. In fact, when people refer to new members of staff as being ‘green’ the term comes from the malleability associated with green wood. But, did you know that ‘green wood’ specifically refers to timber with a moisture content of more than 28%? For us that is significant as it is below this number that shrinkage of timber begins which we must take into account when measuring and building with green timber. See ‘kiln-dried wood’ for comparison.
Header log
Quite simply, this is the horizontal beam which spans across an opening in the log work, taking the structural load from above.
Hewing
We use the technique of ‘hewing’ a lot. Traditionally performed with an axe, this is the process of taking a naturally rounded log and flattening one or more of the surfaces. We might use these as the lowermost logs where flush contact with foundations is required, for example. We also use hewn timbers in our dovetail construction methods where both internal and external faces of the wall are flattened. Hand hewing starts at the base of the tree and works up towards the top. Doing reduces the risk of the broken fibres splitting and running into the timber we wish to keep. These days most log builders generally create flats using a sawmill or chainsaw.
Kiln-dried wood
By contrast to green wood (see above), kiln-dried wood has a moisture content of less than 15%. At this point, much of the shrinkage has already occurred making the timber much more predictable in its behaviour. At BLC, we don’t use a lot of kiln-dried timber. Cutting seamless joints and notches requires the use of more workable green timber with the building drying naturally and settling over time. Log building techniques take all of this settling into account with notches actually becoming tighter over time. All of our timber is sourced directly from the forest.
Log profile
As the name suggests, this is simply the cross sectional profile of the log. However, we use different profiles for different sections of the cabin and/or building techniques. Most typically a cabin log can be round, flat, hewn (D-shaped if only hewn on one side) or bevelled - cut at a specific angle. This term refers mostly to machined log cabins where each log profile is identical, rather than handcrafted.
Mortice
You’ll have seen mortices without perhaps knowing that’s what they were called! A mortice is a square or rectangular slot cut into a log or timber into which another member, called a tenon fits. (see below)
Notch
Where logs intersect, a ‘notch’ must be cut to lock the two logs together. Our most commonly used technique is the Scandinavian Saddle Notch, but some of the other frequently used notches are:
Blind Notch: A notch that does not extend completely through a log. Dovetail Notch: Exactly as per the furniture joint albeit on a much larger scale. A beautiful and architectural joint with precise angles and design. Half Dovetail Notch: Log end where one side only is shaped into the distinctive sloping shape. Round Notch: A notch whereby the profile of the log appears as a partial circle on the underside. Round Ram’s Head Notch: Same as a Ram’s Head Notch (see below) except that the outer cuts retain a rounded
Saddle Notch: A beautiful notch that is triangular in profile, although this is largely hidden once the cabin is complete to form seamless corner joints. Ram’s Head Notch: A notch where two saddles are scribed into one another. Usually used in cabins where large fluted butts are present in the timber to allow for a consistent scribing surface at the notch. Square Notch: Has the appearance of a standard notch on the exterior but inside has a square interlocking lap to add structural integrity and lock the notch together This can be added to a Saddle notch, Ram’s Head notch or a round notch...a ‘Round-Square Notch’
R-value
Thankfully absolutely nothing to do with the rate at which a virus spreads through a population, the R-value we work with is a measure of the timber’s resistance to heat flow. In other words, its ability to act as an insulator. The higher the R-value, the greater the insulating capacity of that material. The massive logs we use have a huge thermal mass meaning they store heat during the day and radiate it out as ambient temperatures drop, reducing the need for additional heating by as much as 15% compared to conventional timber framed houses. See also ‘U-value’ below.
Scribing
The technique of scribing is a highly-skilled process whereby the natural profile of one log is transcribed onto another, allowing the two to sit seamlessly together without gaps. To achieve this, we use a ‘scribe’ - a large compass-like tool is used to mark the contours, lumps and bumps of the log below onto the log being fitted. An accurate scribe is essential for a perfect fit. Scribing is a skill that can be learned in hours but takes years to master. The scribe lines marked on the log to be fitted are precisely cut to achieve the perfect fit to the log below. . This process is repeated, stacking one log on top of another until the desired height of the wall is achieved. Only a log builder knows the sound of a well scribed and cut log being rolled into its final position perfectly as the air is pushed out of the joint and the surfaces locate all at once.
Settling
All our cabins are ‘built green’, using freshly felled timbers. As moisture evaporates and the timbers dry out, shrinkage and ‘settling’ occurs meaning logs lose a certain amount of their overall diameter. Obviously, we factor this into our builds, meaning notches and joints only become tighter and stronger over time. As such, a handcrafted log cabin built by BLC can genuinely last for hundreds of years.
Sleeper log
Despite the name, a sleeper log is actually a really active part of a cabin! It is the name given to a support beam in the ground floor on which the floor joists are fitted.
Tenon
A tenon is the other half of a tenon-and-mortice joint as refers to the square or rectangular protrusion left by removing the timber from around it which fits into the mortice. If the mortice is the lock, the tenon is the key.
U-value
The reciprocal of the R-value (see above), the U-value is the measure of how well, or how badly, a material transmits heat most typically from the inside out. The lower the U-value, the less heat ‘leaks’ through a substance. These calculations are often complex but we can work these out for you if you need SAP or EPC certificates for building regulations and have had our logwork thermally modelled for this purpose
Waney edge
A waney edge refers to the natural contours of the timber. Whilst much of the timber you see in hardware stores and builders’ merchants is square, waney edge timber is simply a planked tree, cut only in one plain, leaving the beautiful undulations and natural characteristics of the wood on the edges. This is particularly attractive when used as a cladding material on the outside of buildings.
We hope this insight into the vocabulary of log building has given you a greater understanding of the calculations, skills and techniques that go into log building and perhaps even cleared up a few mysteries in the process. If there are any other words you’d like cleared up or explained, drop us a line and we’ll reply to you. We may well also feature them in a second edition!