As we have emphasized previously, we are NOT experts in the installation or use of Trestlewood or other wood products (see, for example, our Jan 23, 2014, blog post, "Q: What is the Best Way to Install a Trestlewood Mantel (or Siding or Flooring or...)?"
We have seen and read about some different approaches to wood siding installation and wanted to use this blog post to summarize some of the things that have stood out to us. These thoughts are not represented to be comprehensive or even necessarily completely accurate. Perhaps they can provide a starting point in helping you ask the right questions of wood siding (or other wood product) installation experts that you are considering involving on your project.
Thought #1: Wood is wood and will move.
An article on Woodworkers Source's web site (woodworkerssource.com) says it this way:
"Wood expands and contracts with changes in the surrounding humidity and to a lesser degree the temperature. More humid air will cause wood to expand; drier air will cause wood to contract. This movement cannot be stopped. You can learn what to expect and techniques to cope with the movement." ("Wood Movement and How It Affects Your Woodworking Projects")
Wood moves even when it is inside in a controlled environment. It can be expected to move more when it is used in exterior applications, like siding.
Thought #2: Climatization is crucial.
"The objective is to bring the moisture content of the wood, as close as possible, to the level the finished product will experience in service. Acquire your lumber in advance and give it time to acclimate to the environment in which it will be used or worked. Sometimes it may be necessary to 'stack and sticker' lumber to allow it to properly reach equilibrium with the environment." ("Wood Movement and How It Affects Your Woodworking Projects")
Wood used as exterior siding can be expected to fluctuate somewhat in moisture content (based on season of year, weather, etc.) throughout its life. It will expand as it gains moisture and contract (shrink) as it loses moisture.
Some manufacturers of new wood siding products recommend that undried/unseasoned wood siding be allowed to air dry for at least 30 days (longer in damp or humid conditions), after being stacked on stickers in a dry area with good air flow. We have also noticed that some experts recommend pre-finishing all sides of siding lumber between climatization and installation.
Thought #3: Consider using kiln-dried lumber.
Kiln drying can reduce or sometimes even eliminate the time required for acclimation. That being said, if kiln drying reduces the moisture content of lumber to below the typical moisture content range of the project location, it is probably best to climatize the lumber and allow it to gain some moisture to move to equilibirum moisture content prior to installation. It is possible that lumber that is drier than the environment in which it is installed could take on additional moisture and expand, causing it to buckle. Note also that kiln drying can make lumber more brittle, increasing the likelihood of knots becoming loose and/or falling out (especially if the lumber is being machined.)
Thought #4: Use wood siding products in ways that allow them to move and otherwise be what they are.
Board-on-board and board-and-batten are examples of siding configurations that can allow some board shrinkage to occur without creating gaps in siding coverage. Putting a dark background behind siding that is installed using a configuration that is likely to result in gaps in dry periods (such as a board-to-board configuration) can make such gaps look more natural.
Most Trestlewood lumber/siding products are rustic by nature, with significant rustic character (knots, checking, nail and/or other holes, and/or other.) Wood shrinkage and/or other movement "issues" can often be thought of as just enhancing this rustic character.
Thought #5: If you would like to minimize the impact of movement, use narrower boards and shorter lengths.
Wider and longer boards are impacted more by shrinkage and other movement than narrower and shorter boards.
Thought #6: Keep in mind that adding a profile to or otherwise processing lumber can release stresses in the wood, triggering movement.
Thought #7: Select a contractor and other professionals who know what they are doing (and understand your geographic area and what you are trying to accomplish.)
Thought #8: Use correct installation procedures.
We are not the ones to tell you what this even means. For what it's worth, following is a link to some pre-installation ideas/guidelines published by the Forest Products Laboratory:
"Before You Install Exterior Wood-Based Siding"
We are not saying that this information is complete or that it applies in full to your specific application. We refer you back to Thought #7 and encourage you to select a contractor and other professionals who understand and will use correct installation procedures. We will say that some of the installation principles that experts seem to emphasize include (a) proper climatization; (b) preventing moisture from getting trapped in places/ways that preclude the wood from drying out; and (c) adequately securing siding boards.
Thought #9: Use high-quality fasteners.
We recommend the use of high-quality stainless steel fasteners with our Trestlewood II ("Salty Fir") and Picklewood lumber/siding products to minimize the chances/amount of corrosion. We have noticed that many experts recommend the use of stainless steel fasteners with wood siding products in general (even wood siding products without a salt/mineral content.) This seems like a good recommendation to us. As noted in Thought #8, use enough fasteners to adequately secure siding lumber.
Thought #10: Maintain your siding appropriately.
Maintaining your siding includes achieving and preserving your desired look/appearance and appropriately protecting your siding from moisture and other weather/elements. We defer to your contractor and other professionals for specific product(s) and approach(es) to achieve the desired results, but offer the following thoughts for consideration: