Wood shrinks and swells with change in moisture content. To minimize dimensional change after installation, install siding at a moisture content that matches with local climate as closely as possible. If climate in a particular region causes wood to maintain 8% to 13% moisture content annually, then the most ideal siding would be installed at a moisture content within that range, and the material would be stored, stickered and protected for a week to ten days prior to application.
If unseasoned materials are used, the following considerations are suggested:1) allow for shrinkage by using shorter lengths; 2) use as narrow width as possible; 3) use patterns which allow for some shrinkage (board and batten,channel rustic with an adequate tongue, board on board, narrow bevel, etc. 4) and in-place seasoning before application of finish or 5) pre-staining.
Often material which has been properly seasoned, stored and handled,will pick up moisture after installation and prior to painting. Later, when the siding releases its moisture, joints may open up or buckling may occur.
Extra protection can be given the siding by priming or pre-finishing all sides, after it has reached climatic balance and before it is installed. Pre-finishing can also minimize objectionable unfinished lines where joints open up due to face width shrinkage.
House construction features that will minimize water damage of outside paint are: 1) Wide roof overhang, 2) wide flashing under shingles at roof edges, 3) effective vapor barriers, 4) adequate eave troughs and properly hung downspouts, 5) adequate insulation and ventilation of the attic. If these features are lacking in a new house, persistent paint blistering and peeling may occur. The proper application and nailing of wood siding does much to improve the appearance and durability of both wood and paint by reducing the tendency of the siding to split, crack, and cup with changes in moisture content.
Another important consideration to minimize dimensional change is to install shorter lengths. All installation guides tell you to use as narrow a width as possible. What people forget is that wood also shrinks longitudinally. In other words, the longer the board the more shrinkage along the length.
A twenty foot long board can shrink anywhere between a 1/4" - 1/2". What the old timers knew was that you can minimize the joint gaps by cutting the wood and using more joints. Because most wood in use today is kiln dried the shrinkage on a twenty foot board is closer to 1/4". If you were to cut that board into four pieces, the shrinkage would average 1/16"per joint. That is what the designers of our clapboard saw had in mind. They know that six foot lengths and shorter would ensure tight joints fort he life of the siding.
Nails and Nailing
Good nails and nailing practices are a must in proper application of wood siding. Nail locations are included under individual patterns. However, the following data about nails will be very helpful in the selection and use of the right nail for the right use.
The following requirements are essential for nails used on wood siding:
preferable rustproof. See "types of nails recommended."
Type of Nail Recommended
1) Stainless steel.
Common iron nails or poor-quality galvanized nails corrode easily and will cause unsightly staining of the wood and paint. When the wood is to be left unfinished to weather or finished naturally with light-colored penetrating stains or water-repellent preservatives, only aluminum or stainless steel nails should be used.
Nail penetration and spacing
Suggested sizes are minimal and should be longer when siding is installed over other than wood sheathing and/or sheathing and studs. Recommended penetration into a solid wood base is 11/2", 11/4" with ring shank nails.
Vertical siding should be nailed to blocking or other wood framing members not over 36" on center when face nailed, and 32" on center when blind nailed.
Horizontal siding should be nailed to studs at 24" o.c. maximum when applied over solid sheathing and 16"o.c. maximum when applied without sheathing. Bevel sidings should be nailed at 16" intervals.
Many nails are smooth shanked and will loosen under extremes in temperature changes. Increased holding power may be obtained by using a ring-threaded or spiral-threaded nail shank. These particular shanks are readily available.
The most commonly used nail points include:
Blunt - reduces splitting
For the best possible holding power with the least splitting, a blunt or medium diamond and a blunt or medium needle with a ring-threaded shank are recommended.
The following estimator provides factors for determining the exact amount of material needed for basic types of wood siding.
Multiply square footage to be covered by factor (length x width x factor).
*Allowance for trim and waste should be added.