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 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). » Trex 1 x 4 decking is not recommended for overhang applications with the exception of 1 x 4 decking running perpendicular to the framing.
3/16" (5 mm)
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 heavily wooded areas, Trex ® recommends a 3/8 " (10 mm) gap. No gapping should ever exceed 1/2 " (13 mm).
Width-to-Width Gap
3/16 " (5 mm)
End-to-End
End-to-End/End-to-Width and Abutting Gap
End-to-Width
End-to-End/ End-to-Width Abutting Gap
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)
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 19.
*Temperature at installation.
When using the Trex Hideaway® fasteners, the placement of the hidden fastener establishes the designated gap size.
When installing fascia, gapping guidelines must be followed.
1/4" – 1/2" (6 mm – 13 mm)
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.
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