Installation Guide

32
DECKING
GAPPING and OVERHANG
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 all
Trex decking is 1/2" (13 mm).
» All decks require air circulation to keep them dry and
looking good. To improve air fl ow, leave openings
under the decking or increase gapping to 3/8"
(10 mm).
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 pages 28–29.
Abutting Solid Objects
When decking is abutting a wall, you must also gap it
1/4"–1/2" (6–13 mm) depending on the temperature at
installation. See chart at left.
Width-to-Width
The minimum required width-to-width gapping is
1/4" (6 mm). This is allowed for both hot and cold
weather installations. For docks and heavily wooded
areas, Trex recommends a 3/8" (10 mm) gap as well.
No gapping should ever exceed 1/2" (13 mm).
1/4 "
(6 mm)
*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" (6 mm)
Below 40°F* (4.5°C)* 1/4" (6 mm)
WIDTH-TO-WIDTH GAP
1/8 " – 3/16"
(3 mm – 5 mm)
1/4 " – 1/2"
(6 mm – 13 mm)
Above 40°F* (4.5°C)* 1/8" (3 mm) 1/4" (6 mm)
Below 40°F* (4.5°C)* 3/16" (5 mm) 1/2" (13 mm)
When you use the recommended hidden
fasteners, the placement of the hidden fastener
establishes the designated gap size.
When installing fascia, gapping rules must
apply.
NOTE: Construction methods are always improving. Please refer to www.trex.com for the most up-to-date installation requirements.