Hidden‑fastener systems secure grooved composite or PVC deck boards from the side/edge into the joist using clips that engage a groove so the visible face of the board is free of screw heads and plugs for a cleaner look.[1][2][3]
Two common approaches are (a) simple side/edge clips fastened to each joist that engage a board groove, and (b) proprietary clip+tool systems (examples include CAMO Marksman/CAMO Pro and Cortex/SIDELoc‑style systems) that speed installation and usually set spacing automatically or with a dedicated tool.[2][3][5]
Why spacing and temperature charts matter
Composite and capped‑PVC decking expand and contract primarily along their length with temperature changes, and manufacturers treat linear thermal movement as a primary design constraint when they publish installation instructions.[2][5][6]
Manufacturers publish product‑specific installation guides and temperature‑based gap charts and consistently instruct installers to follow the brand's recommended clip system and gap/spacing chart for that product.[1][2][7]
There is no single universal numeric gap that fits all brands or product families—brands and material types publish different coefficients of thermal expansion (CTEs) and different gap charts, so numeric gap values vary by brand and board family.[1][2][6][5]
Manufacturers provide temperature‑based gap tables for both side‑to‑side and end‑to‑end spacing; installers must measure and install gaps according to the temperature at the time of installation because colder installation temperatures generally require smaller initial gaps.[1][2][3]
DeckMath publishes coefficients of thermal expansion for many brands and offers an Expansion Gap Calculator that computes recommended end‑to‑end gaps for a given material, board length, and installation temperature—this is a practical tool installers can use when the manufacturer's chart or calculator isn't available.[6]
Typical gap ranges and how clips affect spacing
Typical practical side‑to‑side spacing used by clip systems commonly falls in a rough range around 1/16" to 3/16", but the exact spacer value and required side gap depend on the clip system and manufacturer instructions.[1][2][5]
End‑to‑end (butt joint) spacing is usually larger than side gaps and is specified by the manufacturer via a temperature chart or calculated with thermal‑expansion math; blocking or a support joist is commonly required at butt joints per manufacturer guidance.[2][6]
Many clip systems provide a spacer or set spacing automatically (some near ~3/16"), while other systems require the installer to set spacing using the maker's temperature chart or a dedicated tool—check the specific clip's instructions.[3][5][2]
High‑level installation sequence
Inspect and prepare joists: confirm correct joist spacing, plan board runs and butt joint locations, and ensure joists meet the decking maker's structural requirements.[1][2][4]
Install starter board and starter clips per the product guide.[1][2]
Insert hidden clips into the board grooves and fasten clips to each joist (typically one clip per joist crossing) using the manufacturer‑recommended fastener and tool.[1][2][3]
Continue boards and clips while maintaining temperature‑based end and side gaps; follow the manufacturer's temperature chart or calculator for end gaps.[1][2][6]
Install blocking/support at butt joints as required by the guide and finish with recommended fascia/trim and flashing.[2][1]
Clips are typically fastened at every joist crossing (one clip per joist per board edge) unless the manufacturer's instructions indicate otherwise for the specific clip or board profile.[1][2][3]
Fasteners, corrosion resistance, and approved hardware
Use the fasteners and clips specified or approved by the decking manufacturer; many brands require corrosion‑resistant fasteners (stainless or specified coatings) and warn that non‑approved plated/colored screws can corrode, stain, or fail.[2][7]
Manufacturers often prohibit certain plated or coated screws because coatings can fail; follow the minimum fastener specifications in the deck manufacturer's installation guide to avoid staining, corrosion, or mechanical failure.[2][7]
Some manufacturers call out pre‑drilling requirements for certain end or fascia screws (especially for PVC or dense capped composites); follow the manufacturer's drill and fastener instructions to avoid cracking or improper seating.[2][7]
Joist spacing, stiffness, and structural considerations
Hidden‑fastener performance depends on correct joist spacing and stiffness—consult the decking maker's structural tables and the AWC DCA 6 deck guide for required joist spacing and allowable spans because excessive joist spacing can cause deflection and fastener failures.[4][2]
Typical joist on‑center spacing recommendations vary by board type and thickness (common schedules include 12", 16", or 24" o.c. depending on the product); follow the decking maker's structural recommendations for the board you buy.[4][2]
Common installation pitfalls (and how to avoid them)
Failing to use temperature‑based gap charts or calculators, which can lead to buckling or compression problems—always measure ambient board temperature and follow the chart for that temperature.[1][2][5]
Using non‑approved fasteners or clips, risking corrosion, staining, or mechanical failure; only use hardware approved by the deck board manufacturer.[1][2][7]
Not pre‑drilling where the manufacturer requires it (especially PVC or dense capped composites), which can cause cracking or poor seating of end/fascia screws.[2][7]
Insufficient joist support or too‑wide joist spacing leading to excessive deflection and accelerated fastener wear—follow structural tables and DCA 6 guidance.[4][2]
Hidden systems used in very low‑clearance or ground‑contact conditions without consulting the manufacturer; some manufacturers advise against hidden systems where moisture trapping or clearance is an issue.[8][5]
Ledger attachment, flashing, and safety reminders
Ledger attachment and flashing mistakes are leading causes of catastrophic deck collapse; installers must follow DCA 6 and CPSC safety guidance for ledger, flashing, and structural attachments to avoid collapse risks even when using hidden fasteners for the deck boards.[4][9]
Warranty and repair considerations
Many brands condition warranty coverage on proper installation per their published instructions (including approved fasteners, clip systems, and temperature‑based gaps); incorrect installation can jeopardize warranty claims—keep the product installation PDF you followed and note the installation temperature if you need to file a claim.[1][2][7]
Installer checklist (quick reference)
Obtain and read the decking manufacturer's installation PDF and the clip manufacturer's instructions; confirm the clip is approved for your board.[1][2][3]
Measure ambient board temperature and consult the brand's temperature‑based gap chart (or DeckMath's Expansion Gap Calculator if needed) to set end and side gaps before fastening.[2][6]
Confirm joist spacing and stiffness meet the manufacturer's structural tables and DCA 6 recommendations; plan blocking at butt joints and support locations.[4][2]
Use only the fasteners and clips specified by the board maker; use corrosion‑resistant fasteners where required and pre‑drill per guidance for end/fascia screws when called out.[2][7]
Fasten clips at each joist crossing (unless the guide states otherwise) and maintain the specified gaps as you proceed across the deck.
[1][3]
Install flashing and ledger details per DCA 6 and CPSC guidance; inspect for drainage and clearance issues before finishing trim and fascia.[4][9]