Common Industry Terms
Consult this collection of terms and concepts common in the timber frame and log home restoration industry:
Air Dried Logs
Equilibrium Moisture Content (EMC)
Equilibrium Moisture Level (EML)
Exposed Log Ends
Fiber Saturation Point
Kiln Dried Logs
A term used when caulking pulls away from the log surface.
The method of allowing logs to dry naturally over an extended period of time.
Condition causing water to “splash back” onto the log surface such as
decks, ground, landscaping, or any objects too close to the log wall.
Moisture existing in the cell walls. The evaporation of bound water causes the logs to shrink.
Groove in a log profile which allows for the use of backer rod and caulks to properly seal between log courses.
The three primary components in wood cells. Lignin acts as the glue that holds wood cells together.
Filling used between rows of logs. Traditional chinking is mortar-based. Modern synthetic chinking, manufactured to look like traditional chinking, is similar to caulk but with greater elasticity.
Failure occurs when caulking adheres to log surface but the caulking itself tears apart.
The ability of wood to resist the effects of exposure to air, water, and the ultraviolet rays in sunlight. While wood species vary in their resistance, none are completely decay-proof.
A system designed to protect logs by directing the flow of water away from the home such as gutters, sloping grade away from the home and footing drains.
Log profile design in which water draining off a log surface will drip on lower log keeping moisture away from log joints.
Typically logs with moisture content at 19% or below.
The equilibrium moisture content (EMC) occurs when the wood has reached a water content equilibrium with its environment and is no longer gaining or losing moisture. The percent of moisture the log will seek to acclimate to the relative humidity in the area.
The moisture level of the wood will eventually reach equilibrium with that of the surrounding air This equilibrium moisture level (EML) depends principally on the relative humidity of the air. Air temperature has little effect on the equilibrium moisture level over its normal indoor range.
Exposed Log Ends
A term used when the log ends extend beyond roof overhang and are exposed to the elements.
Log homes must have a finish applied that will allow moisture vapor to pass through the finish while water in liquid form is kept out. Using a waterproof finish will trap moisture inside the logs and can cause logs to decay from the inside.
Point in the drying process where cell cavities loose all their free water but bound water remains.
Protection added around doors, windows, chimney and wall terminations to protect against water, air and insect infiltration.
Moisture inside the cell cavity. No shrinkage occurs while logs are losing free water.
Logs with moisture content greater than 19% are called “green” logs. Walls built of green logs can settle up to ¾ inch per foot.
The distance between the ground and the first log course. Higher ground clearance protects lower log courses from backsplash.
The method of drying logs using heated air flow.
Profiles are the various milled shapes of the logs when looking at a cross-section. For example, a flat/round log is flat on one side and round on the other.
The milling process can cause extractives to come to the surface and harden which may adversely affect stain adhesion.
The amount of water contained within the wood. Water contained within the wood may be ‘free water’ found in cell cavities or ‘bound water’ found in the cell walls. Drying of wood does not result in significant shrinkage until all free water has been removed. The point at which no free water remains and shrinkage begins is known as the fiber saturation point (FSP), which occurs at about 28 percent moisture content.
Device used to measure moisture content.
The portion of the roof that extends beyond the log wall. The International Log Builders Association (ILBA) Standards recommends one foot of overhang for every eight feet of log wall height. Longer overhangs help protect lower log courses from the elements.
The loss of log wall height over time. During the first two years when the majority of wall log settling takes place, a wall may lose ¾ inch per foot of wall height. This means that an 8-foot tall wall may lose up to 6 inches in height before it has finished settling. Causes of Settling include
- Substrate Failure – Term used when caulking actually tears the log surface away from the logs.
- Wood Compression – Shrinkage of log diameter as the logs dry to a stable condition. This condition is known as Equilibrium Moisture Content (EMC). EMC is reached when the log moisture content acclimates to the average relative humidity of the home site; Wood compression. Over time, the weight of the structure will compress wood fibers, causing the wall logs to settle. Compression causes less settling than shrinkage
- Wood Shrinkage – Wood shrinks when it dries and swells when it becomes wet. These dimensional changes vary with the species and the orientation of the wood fibers. When wood dries from its green condition, little or no shrinkage occurs until the moisture content falls below the fiber saturation level. At this level, all free moisture has been released from the cell cavities, leaving only the cell walls saturated. The moisture content at which this condition is reached varies but averages 30% (based on the ratio of the weight of water to the oven-dried weight of wood). As the cell walls continue to release moisture, the wood shrinks almost in direct proportion to its moisture loss. That is, for each percentage drop in moisture content, the wood shrinks by about 1/30 of its total potential shrinkage.
Franklin Industries offers the best, most comprehensive range of timber frame and log home restoration services in the industry. Please Contact Us and we will be happy to answer your questions and arrange a quote.