Log Home Construction Methods: Notched or Butt and Pass? Part II

In Part I we defined, in rather simple terms, the basic difference between Butt and Pass and Notched  joinery for log home corners.

Lets now focus on Notched — I’ll refer to this simply as ‘coped’.

As elegant as nothced corners are there are some serious drawbacks that need to be brought to the forefront and discussed.

Keep in mind that as a log dries and the moisture content of a log decreases the log shrinks. A log does not shrink lengthwise it shrinks in diameter.

A log is notched by transferring a portion of the diameter of the log below to the log to be notched by using a scribe or perhaps some other method. The curvature is marked on the log and a craftsman carefully cuts the notch by hand or machine. The finished notch results in a tight fit between the logs.

This is a very strong joint however when you take into account the manner in which a log shrinks this tight fit has great potential lose much of its tight contact with the log below especially if unseasoned or green logs are used.

When a log is notched to the diameter of the log below, the notch cut lengthwise, will remain the same size as the log shrinks however, the diameter of both logs will shrink. The diameter of the log below, that the notch rests upon in a perpendicular manner, also shrinks. This expands the space between the notch and the log on which it was fitted creating a gap around majority of the joint. What was once tight last year or two years ago is now ill-fitting and the log builder is long gone down the road.

Such a gap at the notch provides easy access for water which can wick through the log from the exposed cut area. Moisture retained in the corners will quickly promote rot. Such a gap also provides the perfect cover and protection from the elements for a host of wood munching insects that would love nothing more than to gain easy access.

The impact of this can be devastating as a rotting corner compromises the structural integrity of the home. Even with a proper roof overhang logs will still get wet as rain does not always fall straight down – add just a little wind and you have wet logs. Add snow and ice to the mix and you now have a very serious problem. Water gets into the gap between the notch and the log freezes, thaws, expands, contracts and freezes again.

Since the ends of logs can and will also wick moisture, the exterior bottom portion of the notched log gets a double whammy of moisture: from the end of the log as well as the notch itself.

Exterior stains and preservatives can certainly help to repel moisture at the ends and also on the log itself but the notch is rarely if ever treated with such a preservative. This can lead to another problem. If a stain or preservative is applied to the exterior of a log – a common practice – the oil-based or water-based stain/preservative can be effective in keeping water out. However, if the log is getting soaked from within because it has been wicking water from the notch then the repel action of the stain, seal or preservative is also helping to hold that moisture in preventing the log from being able to dry out.

Try this experiment: put your hand inside a rubber glove – run water over your gloved hand – your hand does not get wet does it? — However leave the glove on for a while and your hand will become wet as your hand sweats and there is no place for the sweat to go. Soon you have a damp hand. The same applies to a log.

If you are speaking with a log home builder make sure that you ask a great deal of questions about this. Many will unfortunately tell you that the shrinkage is insignificant and nothing to worry about – do not take this for an answer.

No matter how tight the notch is made this is a water entry point that must be considered. The worst case scenario of a rotted corner is having to replace the affected log or logs. On a Butt and Pass system log replacement is relatively easy compared to a notched corner system. With notched corners you are looking at a major project and significant investment to fix. Try replacing one of the logs on a wall of a cabin you build with the Lincoln Logs toy without disturbing the entire structure.

I realize that I may have touched a nerve with some folks with regard to the information that I present here — we log home people are a passionate bunch — and we come to the table with differing viewpoints and bias for certain methods of construction. I welcome all viewpoints so feel free to respond.

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