Tuesday, August 12, 2008

Timber Frame Homes - Wood Types

When you’re planning to build a timber frame or post and beam home, there is another consideration in addition to the species of wood you will have.

Green: Green timbers are healthy living trees when harvested from the forest. They typically have a moisture content around 28 percent. The timbers dry for a year or longer after the timber frame is erected. Throughout the drying process the timbers will shrink in the direction perpendicular to the grain of the wood, check (typically small cracks perpendicular to the growth rings running with the grain of the wood) and possibly twisting as they acclimate to the temperature and humidity of the environment. These are characteristic of green lumber and unavoidable, but do not affect the structural integrity of the timber frame. Green timbers are the least expensive option.

Standing Dead: Standing Dead timbers are trees that have been killed by insect infestation, fire, or other means and are still standing in the forest. The timbers are individually selected and harvested and considered a more environmentally conscious choice. More expensive than green timbers, standing dead has a lower moisture content, making it more stable and less apt to twist or check.

Kiln or Air Dried: To hasten the drying process and reduce natural shrinking and checking, you can choose to have your timbers kiln dried or air dried. Timbers that are kiln dried are baked in huge kilns for several weeks. Air drying is done in a warehouse or log yard, where the timbers sit for several months, even years, to dry. Moisture is reduced to 18% to 20% in these processes.

Reclaimed: You could also choose reclaimed wood to build your timber frame or post and beam home. Reclaimed timbers are salvaged from dismantled factories, barns, and bridges. The moisture content is minimal, making them strong and solid. All have a rich history and story to tell, adding to the character of your home. Many have nail and worm holes which can be left exposed. Because of the labor involved in harvesting these timbers, they are one of the most expensive types of wood.

Glue-Laminated Timbers: Glue-laminated timbers are used to span great distances in a timber frame or post and beam home. They are also used in homes made solely of Structural Insulated Panels (also called SIPs or stress skin panels) to support the panels in longer spans. Full trees are brought to a mill, where the bark is removed and the trees are sawn into boards usually no thicker than two inches thick. The boards are then kiln dried for about a week until the moisture content is below 15%, usually around 8%-10% moisture. The boards are then planned smooth. The smooth planks then travel to a machine that applies one of two kinds of glue to the interior boards. One kind of glue reacts with radio frequency to cure the glue in a few minutes, and the other uses a high-pressure clamp which hold the boards together for 24 hours. After drying, the timber runs through a profiler to make sure it is perfectly straight and uniform. Glue-Laminated timbers are very strong and resource efficient, they typically cost more than green lumber but provide greater strength & uniformity.

With all of the options available, aesthetics and strength can be equally addressed and timber types can also be mixed (timber species as well). Consider these options early when building a green home. We can work with you to integrate them and even provide samples during the design process.

Jackie Lampiasi, Marketing Director

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