The Log Cabin

Tuesday, April 13, 2010

The Logs

What type of wood species is best for your log home? There is no quick answer to that question. The simplest answer is whatever species the log home producer you choose offers. Their selection of species is primarily based on location. Besides the species, how the logs are milled, dried and treated effect the quality and durability of the log. The following is an introduction to log basics.

First, I will provide a little terminology primer. You’ve undoubtedly heard the terms hardwood and softwood. Believe it or not, rather than hardness, the distinction has to do with reproduction. Balsa wood is a hardwood. Need I say more? The classification relates to the trees seeds. If they are covered, the tree is a hardwood.

The outside of a log obviously determines its look but it is the inside that determines its durability. A tree is formed first with sapwood. Sapwood conducts sap/water from the tree’s roots to its leaves. Eventually, the inside rings die and become heartwood. The sapwood section continues as the youngest and outermost living wood. Heartwood is resistant to checking, splitting, twisting and decay. It can remain sound for hundreds of years.

The most common log home wood species are:

Eastern white pine great durability - creamy white to light brown - Appalachian and Great Lake states

Northern white cedar high % of heartwood - light to medium or straw brown - Maine and Great Lake states

Western Red Cedar high impermeability to liquids – light milky straw -

Bald Cypress Resistant to rot - medium yellow brown to amber dark brown – Southern states

Douglas Fir strong, used for key structural locations - orange brown to reddish brown – Pacific coast, Rocky mountain states

White Oak light to dark brown – Southern Appalachian and central states

Eastern Spruce creamy white - New England Appalachian states

Yellow Poplar green or greenish brown - Southern states

The key to log stability is moisture content. Logs can be cut from dead trees or live (green trees) which must be dried. The drying process can be slow and natural or accelerated and use heat. The slow open air process will eventually (6 months to over a year) adjust the logs moisture content to that of the prevailing atmosphere. Kiln-drying exposes the logs to oven like heat for a period of two to three weeks. Kiln drying is clearly more expensive but produces logs that will settle very little once in place. The open air dried logs are more susceptible to shrinkage and builders must account for it when constructing doorways and windows. I’m leaning toward the kiln dried logs. It’s more expensive but I want my home tight and settled from day one.

The Log Home Council developed a grading system for logs. Grading relates to the structural integrity of the log rather than its aesthetics. There are 15 criteria that determine a log’s grading. Among these are:

Knots - The larger the knot, the weaker the wood

Slope of grain - Grain running parallel to the length of the log is strongest

Species - Some species meet criteria better than others. For example, yellow poplar loses its moisture content quickly and may check severely.

Moisture content – green are freshly cut trees, dry are seasoned and then kiln dried logs. Logs should have moisture content of less than 19%. Moisture content must be known to determine proper construction of doors and windows.

The bottom line is that you don’t want to build with ungraded logs. Graded logs can be a little more expensive but don’t forget a rule that generally proves out, ‘you get what you pay for.’

A few other log related terms.

Check – crack that develops in log as it dries

Grain – The quality of a log’s annual growth rings.

Knot - A portion of a limb that is in a log. They can reduce the logs strength.

Shrinkage – The decreasing size of logs as they dry

Settlement – Movement of walls over time as logs lose moisture

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