Using Timber Harvested On-Site

Purchasing a property with hundreds of trees presents several challenges along with its gifts. Trees impact just about every aspect of how a well-designed home comes into being. They play a critical role in heating, cooling, lighting, drainage, views, solar power, wind blocking, creation of positive outdoor spaces, and more. Our relationship to our trees began with an assessment of the health and well being of every tree on the eastern half of our property (determined to be the most likely building area). Simultaneously, elevation changes on the property were also mapped. This would help us understand two important things: how many trees were actually there and which way water wanted to flow on the property. It took about a week for a reputable survey crew from our area to catalog the width and species of each tree as well as plotting of elevation changes…Next, our arborist, Katy Bigelow, came to assess tree health.

I’ve written already about the results of her assessment, which highlighted the ill health of a 0.5 acre cluster of diseased Douglas Fir trees (compromised by an invasive root fungus). After the survey and arborist assessments, there was a lot of information to take in. After walking the site with our design team and reviewing what we had learned, it became clear to everyone where the house “wanted” to be. The decision was made to harvest the diseased trees, along with a few healthy trees on the eastern half, to stop the spread of the fungal root rot to other healthy trees. We planned to mill the usable felled trees into lumber, which would be used to build the home. The Living Building Challenge requires that wood used for construction be FSC (Forest Stewardship Council) Certified or come from trees harvested on-site or salvaged from already downed trees.

Thankfully, we have skilled millers and wood workers on Bainbridge Island. We engaged the services of David Kotz, who transformed our trees into fir, cedar, and alder planks. After initial milling took place in June 2017, we then learned about the process of transforming rough milled wood into wood that is suitable for use in the home. First, wood must be dried properly. The moisture content of green or fresh milled wood is generally quite high (exact percent moisture content depends on season of harvest, humidity, etc). To use site-milled wood for interior purposes the moisture content, or MC, must be brought down to 9%, ideally. This will ensure that wood being used does not contract, twist, cup, or split (imagine your newly installed floors, walls, and ceilings changing shape as your wood dried out…not a pleasant thought).

Going from moisture content of 30+% down to 9% takes time, or expensive kiln drying. Kiln drying has some disadvantages: cost and carbon footprint. Having your wood kiln dried dramatically increases cost of milling your own wood. First, because it is heavy and must be trucked substantial distances to and from a facility that has a kiln, the cost or tansport and the embodied carbon footprint of your project increase. Second, there is a  cost per linear board foot to have wood kiln dried…costs add up very quickly (by the way, if you are considering building a home, your motto will be “costs add up quickly.” I digress…) One must also consider that once wood is sufficiently dry, addition costs will accrue in the process of finish-milling/smooth surfacing. This is necessary if your wood will be used for things like casework, flooring, paneling, trim, etc. Lots to consider…So what did we do?

We invested a little time and effort (and not a ton of cash!) in making our own kiln of sorts. Our current rental home has a sizable RV garage and we took advantage of that large space to store and dry our enormous, heavy piles of wood. First, the wood was stacked 7 feet high with spacers, called “stickers,” separating the layers and creating room for air to move and circulate between the boards. With greater surface area for evaporation, drying is quicker. Next, we set up a series of fans at various locations in the garage to encourage air movement, which also speeds drying.

The final important factor to was to pull the moisture coming off the boards out of the air in the garage. We used a high capacity dehumidifier and sealed air gaps to the outside with tape (we didn’t want the humid pacific northwest winter air entering the garage/makeshift kiln, sabotaging our efforts). We emptied the dehumidifier quite frequently at first, but the need for frequent emptying subsided after a month. It’s April now, our moisture readings are looking pretty good, with most boards in the 9-11 % range for MC. As the weather heats up and the outside air dries out, we plan to open the garage and let the natural warm, dry air circulate and bring the boards down to the 9% number.

Moisture meter: slow drying avoids extra costs

When the time comes, we will have a select boards sent away for finishing into tongue and groove wide plank fir flooring, squared off trim boards, and general stock for construction of cabinets and casework. We also have lumber at the property (cedar and alder), currently under tarps, that will be used for siding, decking, and other interior projects (tables and benches). As soon as we have power on site and the weather improves, we will hook up a fan or two to circulate air under the tarps and speed up the drying as summer arrives. By fall, these boards will be ready for finishing for exterior use. We will keep you posted.

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