In determining the grade of wood for exterior siding, the number of knots represent the perceived quality and price. For example, knotty wood is usually around half the price of clear wood. Even if using clear Cedar siding, there is a strong light to dark contrast throughout the pieces of wood. An installer needs to sort for light and dark pieces in order to blend the wood into an even visual flow. If the planks are not sorted by shade, the result will likely be a ‘staccato’ or checkerboard look which may or may not be the visual impact that you want on your siding.

Selection of wood siding begins at the mills. Some mills will sort out the super dark boards so that it is easier to blend the pieces later. You should be aware that in general mills continuously shrink the standards for lumber. This is because the mills are attempting to get a higher yield and the trees are being cut at a younger age. For instance, a piece of lumber may say 8” but may actually be only 7”. Another consideration is that wood expands and contracts, so it is better to have your designer have an allowance for this in your siding design.

There are a number of consideration in selecting design, materials, and nails for your wood siding. Shiplap and some other patterns require face nails. Marine-grade stainless steel siding nails help prevent leaking of the siding. Shadow lines could help hide nails. However, the nails might still be seen if the bits are at a certain angle. Tongue and groove is another technique for installing wood siding.

Various options in wood species are available for siding. Redwood is no longer a good specification for performance, but it is still good as a reclaimed wood selection because of its rarity. Old growth redwood has a close grain. It is extremely rare and relatively expensive, costing upward of $25/ft. Only redwood, cedar, and cypress have natural resistance to rot because of the existence of tannins. Sap redwood and doug fir require relatively high maintenance. Pine was a better quality 300 to 400 years ago, has declined in quality. Moisture exposure during this timeframe is critical to the maturation of the wood species. Modern pine has no more than 6 to 10 growth rings per inch, resulting in pine no longer being rot resistant.

There are a number of other considerations. If you use south facing walls, you may have particular weather concerns. Plan for ground clearance. Clearance helps protect against splash back, both on the roofline and the ground. Allow for even moisture distribution along flashing. If your designer has completed a modern design without rain gutters, the designer must also design for the drainage. Otherwise the water will wear the finish off and the sun will turn the wood black.

Water or moisture can reach the wood siding material in other ways. For instance, splash back water bounces off the ground or ceiling and hits the wall. It helps if the siding starts 18” off the ground or roof trim. Avoid placing lawn or organic material right up against the wall. This minimizes splash back and mildew potential. The construction or material of the building envelope might also trap water or moisture, leading to moisture issues.

You must backseal certain wood species, like pine. If these types of wood siding are installed without backseal, you might not see the effect right away. However, the wood siding can rot from the back. Drainage and air flow are not the same techniques, but both are important to proper installation of wood siding. Leaving a gap between the primary and secondary barriers will allow drainage behind the walls. The rainscreen technique uses furring strips that allow for air and water flow. Another technique is the use of bump gaps.

Trapped water can cause a number of issues. Just a ½” of trapped water can have a similar effect to a 35-mile-per-hour wind on wood siding. Finishing wood on all six sides provides some protection from moisture. Four of the six sides may be completed in the factory, but the butt and cut end of the siding pieces are commonly done on the job site. The type of finish will help determine the maintenance schedule. For example, transparent finishes are generally one to two years, while semi-transparent finishes last three to five years.