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Measure the deck area
Measure length, width, finished height and any steps, picture-frame edges, breaker boards or angled cuts.
Ausdecking Composite Decking Installation Guide
AusDecking professional guide
Composite Decking Installation Guide
A premium step-by-step guide for planning your subframe, setting correct spacing, installing starter clips, fixing boards with hidden clips, detailing joins and finishing with fascia boards.
Plan first
Before you start your decking installation
A clean composite deck starts with a straight, strong and well-ventilated subframe. Confirm the deck height, fall, drainage, joist direction, board layout and trim details before cutting boards.
Check ventilation
Allow airflow under and around the deck. Poor ventilation can increase movement, heat and moisture issues.
Plan joist direction
Deck boards should run perpendicular to joists. Keep joists straight and evenly spaced for a cleaner finish.
Prepare fixings
Have starter clips, hidden fixing clips, screws, drill bits, saw, spacer tools, level and fascia fixings ready.
Estimator
Quick decking estimator
Use this quick guide to calculate deck area and estimate support lines based on the selected joist spacing. This is for planning only, use the AusGrass Decking Calculator for exact materials.
0m²Exact deck area
0Approx. joist support lines
0Approx. number of posts
This calculator is a planning guide only. Final board quantities, breaker boards, fascias, waste, fixing kits and joist quantities depend on your board range, installation direction, cut layout and site design. This is a calculation for the number of posts only, the length of the posts will vary depending on the height of your deck and the depth of the post into the ground. Posts are not necessarily required when installing onto a concrete slab.
Step-by-step
Professional composite decking installation process
Follow each stage in order. The subframe is the most important part of the job, it must be straight, structurally sound, level, ventilated and set out to suit your selected board range.
Step01
Allow expansion gaps around fixed structures
Before fixing boards, allow clearance from walls, posts, steps and other fixed structures so the deck can ventilate and move naturally.
- Allow a minimum 10mm gap from walls or fixed vertical surfaces.
- Keep the edge clear so water and air can move freely.
- Do not force boards hard against brickwork, render, cladding or posts.
- Plan fascia and trim details before cutting your first board.
Pro tip: Use a spacer block while setting out the first board line to keep the expansion gap consistent.
Step02
Install joists perpendicular to boards
Composite decking boards must be supported by a straight subframe. The joists should run perpendicular to the decking boards.
- Set joists at 350–400mm centres for standard residential installation.
- Keep the subframe square, level and securely fixed to footings or supports.
- Check the finished fall so water can drain away from the deck.
- Use double joists where board ends or joins will land.
Quality check: Sight down each joist before fixing boards. Any bow or high spot can show in the finished deck.
Step03
Fix the starter clips in a straight line
Starter clips set the first row of decking. Take your time here because the first board controls the alignment of the rest of the deck.
- Mark a straight reference line along the first row of joists.
- Fix starter clips to each joist using suitable screws.
- Check clips are aligned before inserting the first board.
- Pre-drill where required to reduce the chance of splitting or screw wander.
Alignment tip: Measure from the outside edge at several points before locking down the first board.
Step04
Install each board with hidden fixing clips
After the first board is fixed, install the next row of clips, slide the next board into position and repeat the process across the deck.
- Push each board into the previous row of clips.
- Install hidden clips to the open side of the board at every joist.
- Keep the board gap consistent using the clip system.
- Check board alignment every few rows rather than waiting until the end.
Installation tip: Work from a straight edge and avoid over-tightening clips, which can restrict natural movement.
Step05
Support board joins with a double joist
If your deck requires board joins, install double joists so each board end has its own support and fixing point.
- Do not share one narrow fixing point between two board ends.
- Use double joists under butt joins for stronger support.
- Fix clips and screws into both joists where required.
- Stagger joins where possible for a more natural visual finish.
Join tip: Plan all board joins before installation so they land cleanly on the support structure.
Step06
Leave clearance between double joists
Where double joists are used for joins, allow space between the joists and secure each board end correctly.
- Allow a minimum 10mm gap between double joists.
- Fix the clips and screws to both joists to help prevent movement.
- Keep board end gaps consistent and suited to site conditions.
- Check that the join does not restrict drainage or ventilation.
Detailing tip: Double joists should be installed straight and parallel so the board ends sit evenly.
Step07
Finish exposed ends with fascia boards
Once the deck surface is complete, cover exposed board ends, starter clips and visible subframe edges with AusDecking fascia boards.
- Measure and cut fascia boards to suit the finished deck edge.
- Pre-drill fixing holes for a cleaner finish.
- Fix fascia boards into the joists with suitable timber screws.
- Keep trim lines straight and leave suitable expansion clearance at ends.
Finish tip: Fascia boards give the deck a clean, framed appearance and help hide exposed clips and board ends.
Key decking details made easy
These clean diagrams help customers understand the most important installation details: joist direction, expansion gaps and double-joist support.
Board and joist direction
Boards run perpendicular to joists, with support lines at consistent centres.
Wall clearance
Allow a minimum 10mm around walls and fixed structures.
Double joist at joins
Each board end should be fixed to its own supported joist line.
Larger decks
Joins, fixings and fascia details
A premium composite deck depends on the small details — hidden clip alignment, supported board ends, consistent gaps and clean fascia finishing.
Use double joists at joins
Board ends require proper support so joins stay tight and secure over time.
Keep fixings aligned
Consistent clip placement makes the board lines straighter and the finished deck cleaner.
Protect ventilation
Leave air gaps around edges and do not block drainage below the deck.
Finish with fascia
Fascia boards hide exposed board ends, starter clips and joist edges for a premium result.
Aftercare
Keep your composite deck looking sharp
Composite decking is low maintenance, but basic care keeps the surface cleaner, safer and looking better for longer.
Clean regularly
Wash with water and a mild cleaner when required. Remove dirt, leaves and debris before they settle into the surface texture.
Manage drainage
Keep gaps, edges and drainage points clear so water can leave the deck and air can circulate around the subframe.
Avoid harsh damage
Avoid dragging sharp metal furniture or heavy items across the surface. Use protective pads under outdoor furniture.
Quality control
Common installation issues and how to avoid them
| Issue | Likely cause | Prevention or fix |
|---|---|---|
| Boards look wavy or uneven | Joists are not straight, level or evenly spaced. | Correct the subframe before fixing boards. Check joist height and alignment across the full deck. |
| Board joins separate | Board ends are not supported by double joists or are missing fixings. | Use double joists at butt joins and fix clips or screws into both support lines. |
| Boards bind against walls | Insufficient expansion clearance against fixed structures. | Allow 10mm minimum clearance around walls and fixed surfaces, and avoid blocking airflow. |
| Visible uneven lines | First board or starter clips were not installed straight. | Use a string line or chalk line for starter clips and recheck alignment every few board rows. |
Design details
Types of joins
Larger decks may require board joins along the length of the deck. Choose the join style before installation so the subframe can be set out correctly.
Butt joint
When deck boards require joins along their length, each board end must be supported and fixed independently.
- Install double joists beneath the join.
- Each board end must be supported independently.
- This allows clips and screws to fix each board securely.
- Leave adequate spacing between the two boards to allow for expansion.
Break board
A break board can be used when deck boards require joins along their length, especially on larger deck areas.
- Install double joists beneath the join.
- Each board end must be supported independently.
- The break board removes the need to have butt joins throughout the deck.
- For decks longer than 5.4m, break boards are recommended.
Edge options
Types of finishes
The finish style affects the appearance of the deck edge, the way board ends are hidden and the amount of subframe preparation required.
Flush finish
A flush finish deck is a design choice typically found in smaller decks to make them appear bigger, or for larger decks where a less restricted appearance is preferred.
The decking boards run to the edge of the frame to meet with the fascia board, giving the deck a clean, run-off look.
Picture frame
A picture frame finish creates a framed edge around the deck, giving the installation a more detailed and high-end appearance.
- Plan additional support beneath the border boards.
- Use double joists where board ends are joined.
- Support each board end independently.
- Picture framing can remove the need for butt joins through the main deck area.
Technical data
Performance & installation specifications
Technical reference table for structural loading, joist spacing, board clearance and installation support requirements.
| Performance Criteria | Residential Decking* | Residential Stairs & Landings* | Commercial Decking* |
|---|---|---|---|
| Uniform live load rating | 1.5 kPa | 2.0 kPa | 2.0 kPa |
| Concentrated load rating | 1.8 kN | 2.7 kN | 2.7 kN |
| Maximum joist spacing centre to centre | 400 mm | 400 mm | 300 mm |
| Installation Requirement | Specification |
|---|---|
| Minimum clearance above ground with adequate drainage | 40 mm |
| Minimum clearance above ground without adequate drainage | 90 mm |
| Side spacing between boards | Controlled automatically by clip system |
| End to end board spacing | Refer to expansion gap table |
| Support requirement for edge boards | Full support required |
*Structural ratings and spacing requirements should be confirmed against the applicable system specifications, project conditions and local building code requirements. Load and span values are based on the nominated application type and must not be exceeded. Joist spacing is measured centre to centre and must comply with the specified maximum span requirements. Minimum ground clearance must be maintained to allow adequate airflow and drainage beneath the deck structure. Board side spacing is governed by the fixing clip system, while board end spacing must follow the applicable expansion gap requirements. All perimeter and edge boards must be fully supported by the subframe.
Technical data
Composite decking test results
Summary of technical requirements, testing standards and reported results for AusDecking composite decking.
| Technical Requirement | Standard | Test Results |
|---|---|---|
| Slipperiness, pendulum test, embossed side | EN 15534-1:2014+A1:2017 Section 6.4.2; CEN/TS 15676:2007; EN 15534-4:2014 Section 4.4 | Longitudinal: Mean 65, Min 64. Horizontal: Mean 86, Min 84. |
| Slipperiness, pendulum test, sand side | EN 15534-1:2014+A1:2017 Section 6.4.2; CEN/TS 15676:2007; EN 15534-4:2014 Section 4.4 | Longitudinal: Mean 54, Min 52. Horizontal: Mean 82, Min 82. |
| Falling mass impact resistance | EN 15534-1:2014+A1:2017 Section 7.1.2.1; EN 15534-4:2014 Section 4.5.1 | Type: Hollow profile. Max. Crack length: No crack. Max. Residual indentation: 0.46 mm. |
| Flexural properties | EN 15534-1:2014+A1:2017 Annex A; EN 15534-4:2014 Section 4.5.2 | Bending strength: 22.8 MPa. Modulus of elasticity: 3.0 GPa. Maximum load: Mean 4184 N, Min 4114 N. Deflection at 5000 N: Mean 0.89 mm, Min 0.98 mm. |
| Moisture resistance under cyclic test conditions | EN 15534-1:2014+A1:2017 Section 8.3.2; EN 15534-4:2014 Section 4.5.5 | Original MOR: 28 MPa. Exposure mean MOR: 19.9 MPa. Decrease: 13%. Min MOR: 19.3 MPa. Decrease: 15%. |
| Swelling and water absorption, 24 hours / 28 days immersion | EN 15534-1:2014+A1:2017 Section 8.3.1; EN 15534-4:2014 Section 4.5.5 | Mean swelling: 0.80% thickness, 0.10% width, 0.09% length. Max. swelling: 0.79% thickness, 0.11% width, 0.12% length. Water absorption: Mean 3.8%, Max 3.8%. |
| Boiling test | EN 15534-1:2014+A1:2017 Section 8.3.3; EN 15534-4:2014 Section 4.5.5 | Water absorption in weight: Mean 3.7%, Max 3.8%. |
| Linear thermal expansion coefficient | EN 15534-1:2014+A1:2017 Section 8.3.2; EN 15534-4:2014 Section 4.5.6 | Mean: 41.0 × 10⁻⁶ K⁻¹. |
| Heat reversion | EN 15534-1:2014+A1:2017 Section 9.3; EN 479:2018; EN 15534-4:2014 Section 4.5.7 | Test temperature: 100°C. Mean: 0.03%. |
| Density | BS EN 15534-1:2014+A1:2017 Section 6.2; EN ISO 1183-1:2012 Method A | 1.35 g/cm³. |
| Resistance to artificial weathering | EN 15534-1:2014+A1:2017 Section 8.1; ISO 4892-2:2013 Cycle 1 | Grey scale: 4–5. |
| Toxic elements analysis | As per 94/62/EC and Amendment 2004/12/EC Directive | Lead: ND. Cadmium: ND. Mercury: ND. Chromium VI: ND. |
| Fire classification of construction products and building elements | EN 13501-1:2018 | Cfl-s1. |
| The body voltage, static electrical propensity | EN 1815:2016 | 1.1 kV. |
| Solar Reflectance Index | ASTM E1980-11 | SRI: Low-wind 10. SRI: Medium-wind 10.4. SRI: High-wind 10.7. |
| Sustainability | FSC | External certificate: SGSHK-COC-322164. Certificate CN25/00005282. |
FAQ
Composite decking installation questions
How much gap should I leave from walls?
Allow a minimum 10mm from walls or fixed vertical structures so the deck can ventilate and expand naturally.
What joist spacing is recommended?
For standard residential installation, joists are generally set at 350–400mm centres. Always confirm spacing suits your board range and application.
Do boards need to run perpendicular to joists?
Yes. Composite decking boards should be installed perpendicular to the joists so each board is properly supported.
Do I need double joists at board joins?
Yes. Where board ends meet, double joists provide proper support and a separate fixing point for each board end.
Should fascia boards be pre-drilled?
Pre-drilling is recommended for a cleaner finish and to help prevent screw movement or damage during fixing.
Ready to install your composite deck?
Choose your AusDecking boards, calculate the materials required and add the correct hidden fixing kit and fascia boards before starting your project.
