Do I have to cut or trim the fence material?

It may be necessary to cut the Trex composite fence material to get the actual length you need to build the fence. The actual lengths of the Trex composite components may vary from the nominal lengths. This is due to expansion and contraction of the material during production. To compensate for possible variation in length, Trex overruns a component before cutting it during the extrusion process. That may add to the length of the component by as much 2", although the typical overrun is less than an inch.

The nominal lengths for Trex materials are as follows:

Trex Posts:

96", 108", and 144"

Trex Pickets:

67" (For Seclusions: used as vertical pickets for 6' tall Seclusions fence panels; can be used for 6' wide on center as bottom rail covers / For Horizons: used as horizontal pickets for 6' wide on center (actual width of a Horizons fence panel is one inch wider than Seclusions))
91" (used as vertical pickets for 8' tall Seclusions fence panels and bottom rail covers for 8' wide on center for any fence height / For Horizons: used as horizontal pickets for 8' wide on center (actual width of a Horizons fence panel is one inch wider than Seclusions))

Trex Top Rails: