Longer Length Siding. Longer length sidings are generally extended versions of standard size siding products. Standard sidings are usually 12’ to 12-1/2’ long. With standard siding panels, seams appear every two to three feet. Longer length sidings are typically offered in 16’, 20’ and 25’ ranges. The primary benefit of longer length siding panels is that it reduces the number of seams on the wall. Siding seams can be an aesthetic objection to vinyl siding. With longer length panels, there are fewer seams. For example, on a 20’ wall, a 16’ panel creates 35% fewer seams than a standard size panel, and a 20’ panel reduces seams by 100%. In short, the longer the panel the fewer seams. Longer lengths can also reduce the amount of time required to install siding since more area can be covered with fewer panels. Most longer length sidings are designed to be installed with their standard-size counterparts so that various sizes can be used together on a project for efficient utilization of material. CertainTeed offers our CedarBoards™ XL, our insulated siding in 16’8” length and Monogram™ 46L; is available in 16’8” in D4 Clapboard, 16’ in D5 Dutchlap as well as 20’ lengths in both D4 Clapboard and D5 Dutchlap.