Can Vinyl Siding Touch Pressure-Treated Wood?

Seasonal Movement

• All building materials are subject to the laws of nature, and one of those laws is that things swell during the summer months when the heat causes the molecules to expand, and then they shrink back down again in the winter months when it is cold. This is known as seasonal movement. If movement isn’t provided for a building material, buckling, cracking and shearing are possibilities that can arise, ruining the finished product and causing costly repairs.

Nature of Vinyl

• Vinyl not only swells in the summer months and shrinks in the winter months, but it also moves somewhat with the weather. Because it is a flexible product, excessive winds can cause the pieces to move somewhat. But settling of the house will also cause movement. Because all homes settle eventually into the dirt the house is built on, the materials attached to the home will also settle. If the vinyl is touching the wood, it will cause the vinyl to rip off the wall.

Wood Swelling

• Not only does wood swell in the heat, but it will also swell when it is exposed to water. This can come in the form of condensation as a result of high humidity levels, or it can be from something as simple as a rainstorm on a cloudy summer afternoon. If extra space isn’t allowed between the edge of the wood where it meets the vinyl siding, the wood will swell to the point that it presses against the siding, causing the vinyl to crack or rip off and the wood decking to buckle and pop up off the joists.

Space

• There are two methods that can be used for the space between the pressure-treated wood pieces and the vinyl siding. You can leave a 1/4-inch gap between the two materials to allow for seasonal movement and swelling, or you can caulk the joint. Caulking is the best option if you prefer not to have the joint visible and open. Because the caulking is flexible, it won’t cause sufficient pressure to damage the surrounding materials.