Gapping and Overhang Requirements
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 timber joist system. » ALWAYS follow Trex-recommended gapping guidelines. » Maximum allowable perpendicular overhang for all Trex decking is 13 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 1 0 mm. » See additional pages for detailed gapping requirements .
5 mm
Width-to-Width The minimum required width-to-width gapping is 5 mm. This is allowed for both hot and cold weather installations. For docks and heavily timbered areas, Trex recommends a 10 mm gap. No gapping should ever exceed 13 mm.
Width-to-Width Gap
5 mm
3 mm – 5 mm
End-to-End/End-to-Width and Abutting Gap End-to-End/ End-to-Width Abutting Gap Above 5°C* 3 mm 6 mm Below 5°C* 5 mm 13 mm
1/8 " – 3/16 "
(3 mm – 5 mm)
3 mm – 5 mm
*Temperature at installation.
When you use the recommended hidden fasteners, the placement of the hidden fastener establishes the designated gap size.
End-to-End Gap Trex decking end-to-end, based upon the temperature at installation. End-to-Width
When installing fascia, gapping rules must apply.
6 mm – 13 mm
6 mm – 13 mm
6 mm – 13 mm
Abutting Solid Objects When decking is abutting a wall, you must also gap it 6–13 mm depending on the temperature at installation.
NOTE: Construction methods are always improving. Please refer to www.trex.com (and your country) for the most up-to-date installation requirements.
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