Construction Process of a Timber Frame: Wood Drying
At Woodhouse, we pride ourselves on providing the highest quality timber frame packages in the industry. We start with the finest timbers and produce a hand-finished timber frame product that is of the highest craftsmanship.
For many reasons, we begin with green timbers, rather than dried. Both air-drying and kiln drying provide obstacles to the timber frame process. Air drying can take years to accomplish. Oak timbers typically dry at a rate of ½ inch per year, while pine and fir timbers dry at around 1 inch per year. Rather than waiting for timbers to dry before joining your frame, we prefer to let the timbers dry and strengthen as part of your timber frame home. Kiln drying is a faster option, but it is incredibly expensive due to the high energy consumption required. The timber frame home industry is well known for being environmentally responsible. Drying timbers up front with the use of a kiln uses unnecessary energy consumption, when timbers will dry naturally in time. One exception is our use of Southern Yellow Pine, a particularly volatile wood species that must be kiln dried before joined to maintain the integrity of the wood.
Drying Timbers For a Timber Frame
There are three ways water is stored inside the wood. The first of which is called free water, which is liquid water found in the cell cavities inside the timbers. This form of water dries naturally in the wood through the use of capillary action. This force pulls the free water out of the wood through both adhesion (attraction of water and other materials) and cohesion (attraction of water to more water). The next is stored as water vapor, which is trapped in the air inside the wood in the cell lumens. Finally, bound water is actually part of the cell wall. Removing this water will shrink the wood itself. This is the hardest form of water to remove from the wood, and will be the last remaining water when the wood reaches its “fiber saturation point.” At this point, the moisture content in the wood is about 25-30%.
As you can imagine, when discussing the manner in which wood dries, a bit of science is involved. If the relative humidity is kept constant, the higher the temperature = the higher the drying rate of the wood. Similarly, if the temperature is kept constant, a lower relative humidity = a higher drying rate of wood. It is important to note that higher drying rates are not always desirable. The drying process begins from the exterior working its way to the center of the wood. Therefore, there is a tendency for the outer layers of the timber to dry faster than the inner layers. Since the outer layers’ ability to shrink is deterred by the wet interior layers, checks and cracks can occur in the wood timbers. It is extremely unlikely for these checks to cause harm to the structural strength and integrity of the timber frame, especially since Woodhouse uses only the highest quality timber to begin the timber framing process.
The timber frame experts in our joinery shop are experienced in the drying of timbers and can account for the future shrinkage in your home. Since you don’t want your timber frame to dry too rapidly, it is important to pay close attention to temperature and humidity in your home throughout the first few years. A good tip is to keep the heat reduced during the first winter season in your new home, and to use a humidifier.
You can take comfort in knowing that as the years go by, your timber frame home is slowly drying, and thus becoming more strong and durable. If you have questions about how Woodhouse prepares the timbers for your timber frame home, give us a call at 800-227-4311 and we’d be happy to explain in greater detail.