Why Does Plastic Siding Bend?

Manufacturing

• Vinyl siding is made from polyvinyl chloride that’s heated until it melts. Additives, including plasticizers, stabilizers, UV radiation absorbers, pigments and fillers are blended into the polyvinyl chloride resin, and the molten PVC is formed into sheets by forcing it out through a mold. Each of the additives has a specific purpose. Stabilizers prevent oxidation; UV radiation absorbers prevent fading; pigments add color and plasticizers provide flexibility.

Plasticizers

• Most plasticizers impart specific properties to the material they’re blended with. According to Dr. Allen Godwin, a senior research associate for ExxonMobil Chemical, plasticizers preferred for manufacturing vinyl siding include DINP, DIDP, DPHP and L9P. These plasticizers are more permanent and weather resistant, making them a good choice for outdoor applications such as vinyl siding. Other plasticizers, including C1-C7 phthalates, trimellitates, citrates and natural oil plasticizers are not preferred.

Gauge

• Vinyl siding comes in several gauges. Thicker gauges are more rigid and won’t bend as much, as are panels with a folded-over, doubled nailing hem. Thicker gauges also cost more, but they’ll last longer. Standard siding is about .045 inches thick, but thinner siding, between .035 and .040 inches, is available. Thinner siding is more likely to sag. Premium brands may be up to .055 inches thick.

Sunlight

• Vinyl siding expands when it’s exposed to heat such as that from sunlight. This can cause it to buckle and warp. Since dark colors absorb heat, vinyl siding has traditionally only been available in light colors. Today, special additives can be added to stabilize the vinyl, making some dark colors available, too.

Installation

• Vinyl siding’s flexibility means you need to make sure you install it correctly to avoid problems. Proper nailing is important. If you nail it too tight, the siding will buckle and wave in the heat of the sun. Loose nailing will allow it to flap in the wind. Leave about 1/32-inch clearance between the head of the nail and the vinyl siding. This is about the thickness of a dime.