Composite decking (Trex, TimberTech, AZEK) is the modern alternative to wood decking — won't rot, won't splinter, doesn't need staining. Lasts 25-30 years vs wood's 10-15. Install is similar to wood decking with one critical addition: hidden fastening systems that allow expansion/contraction with temperature changes. This guide covers a typical composite deck install over an existing structural framing.
For new deck construction (framing, joists, ledger), see related deck-construction guides.
- Skill level
- Advanced
- Time
- 1–3 days for typical deck
- Steps
- 9
- Tools
- 7, listed below
- Materials
- 4, listed below
Before you start
Three things to settle:
1. Hidden fasteners or face screws. Composite decking installs with hidden fastener systems (clips between boards) for clean appearance with no visible screws. Or face screws (visible) for cheaper, faster install. Hidden fasteners cost more but look better.
2. Joist spacing. Standard composite decking requires joists 16 inches on centre. Some lighter composites or longer spans require 12 inches on centre. Verify your specific decking's spec — wrong joist spacing causes sag and warranty void.
3. Expansion gaps. Composite expands and contracts with temperature. End-to-end gaps: 1/8 to 1/4 inch between boards depending on temperature at install. Side-to-side: typically 1/4 inch between boards. Without gaps, boards buckle in summer or develop visible gaps in winter.
What you'll need
Tools
- Cordless drill with bits
- Mitre saw or circular saw
- Hidden fastener kit (proprietary to brand)
- Tape measure and pencil
- Speed square
- Spacers (1/4 inch, included in some kits)
- Knee pads
Materials
- Composite decking boards
- Hidden fastener clips (matching brand)
- Stainless steel deck screws (for face screwing if applicable)
- Joist tape (protects framing from water)
Composite isn't infinitely durable
Composite decking won't rot or splinter, but it does scratch (heavy furniture, dropped tools). It also gets very hot in direct sun — surface temperatures over 60°C in mid-summer can burn bare feet.
Match composite type to your deck's exposure. Capped composites (with polymer top layer) are more scratch-resistant than uncapped.
Step-by-step instructions
Inspect framing
Verify joists are 16 inches on centre (or 12 inches if specified by composite brand for span/load).
Check joists for damage, level, plumb. Repair before decking install.
Apply joist tape (self-adhesive moisture barrier) over joist tops. Protects framing from water seeping through deck board gaps.
Plan layout
Decide direction of deck boards — typically perpendicular to longest dimension.
Plan starter board location — typically away from house wall, with 1/4 inch gap from wall for ventilation.
Install starter board
First board is face-screwed (visible screws) or installed with the kit's starter clips.
Position 1/4 inch from house or rim joist.
Drive stainless steel deck screws every 12-16 inches into joists below.
Install hidden fasteners
Hidden fastener kits use clips that screw into joists between boards. Each clip secures the previous board's edge and creates the spacing for the next board.
Place a clip at each joist position, alternating with each board.
Drive included screws to anchor clips.
Install subsequent boards
Slide each new board's edge into the previous board's clips. The clip's spacing arm sets the gap automatically.
Add new clips at each joist position to secure this board's far edge.
Continue across the deck.
Cut boards to length and at obstacles
Cut to length with mitre saw. Composite cuts cleanly with carbide blades.
End-to-end butt joints between boards: 1/8 inch gap to allow expansion. Use spacers.
Stagger end joints
End joints in adjacent rows should be at least 12 inches apart. Stagger as deck boards continue across joists.
Plan piece lengths for staggering — sometimes requires sacrificing 6-12 inches of cut-off.
Install picture-frame border (optional)
Some installations finish with a 'picture frame' — boards run perpendicular to main deck around the perimeter.
Adds visual finish; covers cut ends of main deck boards.
Mitre corners at 45 degrees.
Install fascia and skirting
Fascia: vertical composite board covering the rim joist's outer face. Hides framing for clean look.
Skirting: optional vertical boards below the deck around perimeter, hiding the underside.
Use composite fascia matching deck colour.
Common mistakes that cost you
- Joist spacing too wide. Composite sags between joists. Always 16 inches on centre minimum.
- No expansion gaps. Boards buckle in summer. Always leave gaps per manufacturer spec.
- Wrong screws. Regular screws corrode in pressure-treated wood. Use stainless steel only.
- Skipping joist tape. Water seeping through gaps rots joist tops. Tape protects framing.
- Aligned end joints. Visible pattern. Stagger end joints 12 inches minimum between rows.
Frequently asked questions
How long does composite decking last?
25-30 years typical, with 25-year warranties common. Better than wood's 10-15 years.
Surface scratches accumulate over time. Capped composite resists scratching better than uncapped.
Composite or pressure-treated wood?
Composite: longer life, no maintenance, higher upfront material cost.
Pressure-treated: lower upfront material cost, needs annual maintenance, splinters with age, replace every 10-15 years.
Most modern deck builds choose composite for the lower lifecycle cost.
What joist spacing does composite decking need?
Standard composite decking needs joists at 16 inches on centre, and some lighter composites or longer spans call for 12 inches on centre. Check the specific decking's specification, because joist spacing that is too wide lets the boards sag and voids the warranty.
Before decking, inspect the joists for damage, level and plumb, make any repairs, and apply self-adhesive joist tape over the joist tops to protect the framing from water.
How much gap should I leave between composite deck boards?
Leave about 1/4 inch side to side between composite deck boards and 1/8 to 1/4 inch at end-to-end butt joints, depending on the temperature at install. Composite expands and contracts with temperature, so boards laid without gaps buckle in summer or open visible gaps in winter.
Hidden fastener clips set the side gap automatically as each board slides in. Keep the starter board 1/4 inch from the house wall for ventilation.
What screws should I use for composite decking?
Use stainless steel deck screws for composite decking, because regular screws corrode in pressure-treated framing. The starter board is face-screwed every 12 to 16 inches into the joists or held with the kit's starter clips. After that, hidden fastener clips screw into each joist between boards, securing one board's edge and setting the gap for the next. Stagger end joints in adjacent rows at least 12 inches apart.
When to call us instead
Deck building is a multi-trade renovation involving framing, decking, railing, and exterior finish. We do decks as fixed-price scopes with permits, materials, and finish.
Book a free 60-minute site visit →Dream Touch Renovations · 33 Roydon Pl, Suite 210, Ottawa, ON K2E 1A3 · (613) 862-4555
Renovating homes across Ottawa, Kanata, Nepean, Barrhaven, Orléans and Stittsville.
Related Ottawa services
If you're building or replacing a deck, our renovation team handles framing, decking, and railing as fixed-price work. Book a free 60-minute consultation.
Official references
- Do I need a building permit?, City of Ottawa
- O. Reg. 163/24: Building Code, Government of Ontario