Installation Guide

18
DECKING
NOTE: Construction methods are always improving. Please refer to www.trex.com for the most up-to-date installation requirements.
1/4" – 1/2"
(6 mm – 13 mm)
3/16"
(5 mm)
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 shrinkage of
the wood joist system.
» ALWAYS follow Trex-recommended
gapping guidelines.
» Maximum allowable perpendicular overhang for all
Trex decking is 3/4" (19 mm).
» 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" (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 page 13.
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 to the left.
Width-to-Width
The minimum required width-to-width gapping is
3/16" (5 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. No
gapping should ever exceed 1/2" (13 mm).
*Temperature at installation.
End-to-End/End-to-Width and Abutting Gap
End-to-End/
End-to-Width
Abutting Gap
3/16" (5 mm)
Width-to-Width Gap
1/8" – 3/16"
(3 mm – 5 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.
1/8" – 3/16"
(3 mm – 5 mm)