Installation Guide

34
DECKING
GAPPING
You must gap Trex
®
decking, both end-to-end and
width-to-width. Gapping is necessary for drainage and
the slight thermal expansion and contraction of Trex
decking boards. Gapping also allows for the shrinkage
of the wood joist system.
» ALWAYS follow Trex-recommended gapping
guidelines.
» Maximum allowable perpendicular overhang for Trex
is 4" (10.2 cm).
» All decks require air circulation to keep them dry and
looking good. To improve air flow, leave openings
under the decking or increase gapping to 3 / 8 " (1 cm).
End-to-End/End-to-Width
Gap Trex decking end-to-end, based upon the
temperature at installation. See chart at left.
For fastening tips, see page 31.
Abutting Solid Objects
When decking is abutting a wall, you must also gap it
1/4" - 1/2" (0.6 - 1.3 cm) depending on the temperature
at installation. See chart at left.
Width-to-Width
The minimum required width-to-width gapping is
1 /4" (0.6 cm). When installing in temperatures below
40°F (4.5°C), Trex recommends 3/8" (1 cm) gapping.
For docks and heavily wooded areas, Trex recommends
a 3/8" (1 cm) gap as well. No gapping should ever
exceed 1/2" (1.3 cm).
1/4" – 3/8"
(0.6 cm – 1 cm)
*Temperature at installation.
*Temperature at installation.
END-TO-END/END-TO-WIDTH AND ABUTTING GAP
End-to-End/
End-to-Width
Abutting Gap
Above 40°F* (4.5°C)* 1/4" (0.6 cm)
Below 40°F* (4.5°C)* 3/8" (1 cm)
WIDTH-TO-WIDTH GAP
When you use the recommended hidden
fasteners, the placement of the hidden fastener
establishes the designated gap size.
1/8" – 3/16"
(0.3 cm – 0.5 cm)
1/4" – 1/2"
(0.6 cm – 1.3 cm)
Above 40˚ F* (4.5 C)* 1/8" (0.3 cm) 1/4" (0.6 cm)
Below 40˚ F* (4.5 C)* 3/16" (0.5 cm) 1/2" (1.3 cm)
When installing fascia, gapping rules must
apply.