Sylvan Composite Decking is a brand of Sylvan Property Enterprise Limited · Unit 21 Olympus Business Park, Kingsteignton Road, Newton Abbot, Devon, TQ12 2SN
Sylvan Deck Designer
Decking design & layout
Welcome to the Sylvan Decking Product — this app will give you a detailed guide to the preparation of your site, sub-structure, decking structure and the best decking board formation. You will ultimately have a decking plan to send to your supplier for a quote.
The app is a good tool for the whole process but it is important that construction follows the complete Installation Guide.
The Sylvan Product Brochure 2026 has the latest composite decking colours, ranges and finishes. Open in new tab
Full Installation Guide
Read online, download a copy, or print the complete Sylvan guide.
Sylvan Decking Design App
Guidance is illustrative please see Full Installation Guide.
Re-open a saved design
Choose the editable design file saved on your device to continue where you left off.
Before you start — installation instructions
All boards are WPC composite, 150 mm × 25 mm × 4000 mm — pick the board type, then a colour and surface finish.
1 · Board type
2 · Colour
3 · Surface finish
Your board selection
Hollow Board — Anthracite — Wood-grain finish
WPC composite board, 150 mm × 25 mm × 4000 mm.
Stocked item
Happy with this board? Continue to the decking outline below — you can come back and change it at any time.
Straight four-sided deck
ALength: 6.00 mBWidth: 4.00 m
Plot outline · 24.00 m² · perimeter 20.00 m.
You need to select every edge
Tap each row below (or the drawing that appears afterwards) to mark it as open ended or wall / structure. The drawing updates once you have made your selections.
20.00 m open ended · 0.00 m against wall / structure
Step 2a · Tap an edge to switch between open ended and wall
ALength: 6.00 mBWidth: 4.00 m
Tap an edge on the drawing or a row below to switch between open ended and wall.
The open ends of the structure may have visible substructure which may need to be hidden — you can do this by placing a decking board across the side.
0 fascia edges · 0.00 m run.
The substructure frame stays at the original size entered above: 24.00 m². With the fascia selected the deck coverage area increases to 24.00 m². Do not use the larger figure for the structure build — use it only for the finished deck coverage and fascia set-out.
A decking board fitted on edge to cover the sub structure frame. Only available on open edges.
Step 2b · Fascia / skirt boards
| Measurement | Value |
|---|---|
| Substructure size | 6.00 m × 4.00 m |
| Substructure area | 24.00 m² |
| Fascia / skirt edges | None chosen |
| Deck coverage size | 6.00 m × 4.00 m |
| Deck coverage area | 24.00 m² |
Coverage area includes the substructure frame plus any fascia / skirt board on open edges. Any board overhang is decided later in the edging section.
Joist selection before spacing and other options
Based on the coverage area 24.00 m², on a 4.00 m × 150 mm board.
Most efficient alternative: horizontal joists. Boards run across the joists, so pick the joist direction that matches your preferred layout.
Fascia boards are never included in the deck board count above.
Board direction key
Boards run vertical
Boards run across the joists. Layout confirmed at the decking design stage.
Composite boards expand and contract with temperature, so gapping must be built into the layout. Side gaps are set with a 7 mm spacing block as each board is fixed; end gaps depend on board length and the temperature on the day of installation.
These are the joint specifications in your build.
Read full extract from installation guide▼
Gaps between decking boards must be allowed, either end to end or side to side. This is for proper drainage and for the slight thermal expansion and contraction of the boards.
- Side-to-side: The gap between board sides is fixed at 7 mm using a 7 mm spacing block.
- End-to-end: The gap between board ends depends on three factors: the length of the board, the temperature when installing and the local highest temperature. The gapping is simplified in the gapping chart above.
- End-to-object: The gap between board end and solid object, like wall or skirting, is also required. See the gapping chart above.
- Side-to-object: The gap of board side to solid object shall be 5 mm minimum.
Decking gapping chart (minimum) — for East Asia and Europe where the highest temperature is no more than 55°C. Two deck board lengths need to be added together in calculating their joint gap.
The basic rule of gapping between board ends: for each 30°C difference between the temperature at installation and your local highest temperature annually, a gap of 1 mm per metre length of the deck board must be allowed. For example, you install deck boards of 4 m length at 25°C and your local highest temperature is 55°C, then your gapping should be calculated as: (4 m + 4 m) x 1 mm x (55°C - 25°C) / 30°C = 8 mm.
Golden Rule: The gap of end-to-end and end-to-object must be allowed well enough.
| Temp at installation | End–end per m | End–end min | End–object per m | End–object min |
|---|---|---|---|---|
| Above 25°C | 1 mm | 4 mm | 2.5 mm | 6 mm |
| Below 25°C | 1.5 mm | 6 mm | 3 mm | 8 mm |
Decking gapping chart (minimum) for Europe where the highest annual temperature is no more than 55°C. Two board lengths are added together when calculating a joint gap. Guidance is illustrative — please see the Full Installation Guide.
Select Temperature at installation
It should be noted that the joint space on a butt end-to-end board varies by the board length. The indication above of 12 mm is based on a 4.0 m + 4.0 m board = 8 m × 1.50 (installation at less than 25°C). However, if you split the 8 m run into 3 boards of 2.67 m, the space between the boards becomes 8 mm (2.67 × 2 × 1.50). There is good board-laying flexibility, such as a brick formation, rather than laying full or long lengths.
The layout should be discussed with your installer.
Side to side
7 mm
Set with a 7 mm spacing block between board edges.
Side to object
5 mm min
Board side to wall or solid object.
End to end
12 mm
1.5 mm per metre × two board lengths (4.0 m + 4.0 m), minimum 6 mm. This is the worst case — two full-length boards meeting — and it is applied to every butt joint on the deck so all joints are the same width.
End to object
12 mm
3 mm per metre × 4.0 m, minimum 8 mm.
The board run is fixed by the sub structure - the joists which results in a (horizontal) board run. Two variables remain: the angle the boards are laid at, and how the end-to-end butt joints line up. All figures below include the 7 mm side gap and the 12 mm end gap.
Where a shorter piece meets a full board the theoretical gap would be less, but the plan standardises on the largest end gap (12 mm) for every joint — so joints line up visually and full expansion is always allowed for.
Fascia / skirt boards
None selected in the Substructure and Decking Coverage & Planning - stage 2 — . If a fascia / skirt board is needed on an open edge, re-open The Substructure and Decking Coverage Plan section add it in Stage 2 (+25 mm per edge) and this plan updates automatically.
Board angle
Design tool — not a construction drawing. Measure on site.
Max angle 41° — limited by the 400 mm unsupported span at 300 mm centres. No board piece under 600 mm is used.
Board runs
This plan gives the board runs. End-to-end joint positions, double joists and noggins are set out on site — use the board run info sheet below to see where joints will fall.
Board run info sheet (A4 print)
Information sheet only. It shows the board runs, not a setting-out plan. Board runs will be increased with any end-to-end joints as per the expansion spacing requirements. Decide joint positions on site; every butt joint must be supported by a joist or a noggin.
Board
4.00 m × 150 mm
Board run
vertical (straight)
Runs listed
39
Side gap / End to End Board Gap allowance
7 mm / 12 mm
| Row | Run length (m) |
|---|---|
| 1 | 4.00 |
| 2 | 4.00 |
| 3 | 4.00 |
| 4 | 4.00 |
| 5 | 4.00 |
| 6 | 4.00 |
| 7 | 4.00 |
| 8 | 4.00 |
| 9 | 4.00 |
| 10 | 4.00 |
| 11 | 4.00 |
| 12 | 4.00 |
| 13 | 4.00 |
| 14 | 4.00 |
| 15 | 4.00 |
| 16 | 4.00 |
| 17 | 4.00 |
| 18 | 4.00 |
| 19 | 4.00 |
| 20 | 4.00 |
| 21 | 4.00 |
| 22 | 4.00 |
| 23 | 4.00 |
| 24 | 4.00 |
| 25 | 4.00 |
| 26 | 4.00 |
| 27 | 4.00 |
| 28 | 4.00 |
| 29 | 4.00 |
| 30 | 4.00 |
| 31 | 4.00 |
| 32 | 4.00 |
| 33 | 4.00 |
| 34 | 4.00 |
| 35 | 4.00 |
| 36 | 4.00 |
| 37 | 4.00 |
| 38 | 4.00 |
| 39 | 4.00 |
| Total | 156.00 |
Every end-to-end joint must be supported — double joist or noggin under each joint.
| Board | 4.00 m × 150 mm |
| Coverage area | 24.00 m² |
| End to End Board Gap allowance | 12 mm |
| Rows across the deck | 39 |
| Average run length | 3.92 m |
Decking Plan before Edging Basis: 4.00 m boards
A check drawing before the plan is locked: perimeter clearance, side gaps, butt-joint gaps and the board size all shown together.
Perimeter clearance
0 mm to walls / structures
Side to side gap
7 mm (use a 7 mm spacing block)
End to End Board Gap allowance
12 mm
End to fixed object
12 mm
Board
4.00 m × 150 mm
Based on 4.00 m board lengths (150 mm wide).
Design only — not a construction drawing. Everything depends on the finished setting out on site. Guidance is illustrative, please see the Full Installation Guide.
Edging is only applied to the open edges — anything butting up to a wall or structure is excluded. Long edges run with the boards; butt ends run across the board ends.
The edge finish can make a big difference to the look of your deck. The ultimate finish is The Picture Frame. The Picture Frame is a uniform edging around the whole decking area and you have a choice of two edging:
- A solid bull nose board (rounded outer edge). The Board is 4 m x 150 mm x 25 mm.
- A right angle edging strip 50 mm x 50 mm. The cost differential between the 2 is significant with the bull nose finish being 3 to 4 times more in material cost. The bull nose may also require extra joists and/or noggins for support.
Overhead view drawn to scale for a 6.00 m × 4.00 m deck. The bullnose adds a 150 mm board on every side; the right-angle strip adds only 50 mm. Finished deck boards hide the joists beneath.
Choose your edging
Edging Solutions
Shown in your chosen board colour: anthracite.
- Flush finish sitting on top of the board — no trip hazard
- Runs along open edges and across board butt ends
- Lowest-cost edging option
- Clips into the open end of the board
- Neat finish where board ends are exposed
- Used where a full edging run is not needed
- Solid board with a rounded outer edge — 4.00 m x 150 mm x 25 mm
- Premium "picture frame" finish
- 3–4x the material cost of the right angle strip; may need extra joists/noggins
No edging selected — nothing is added to the estimate for the perimeter.
Your edging map — check your edging
No finishing edge
Your full design
Check your design below, download a PDF copy to keep, then send it for a quote.
- Shape
- Rectangle / square — 6m length, 4m width
- Board
- Hollow Board — Anthracite — Wood-grain finish
- Deck area
- 24.00 m²
- Perimeter
- 20.00 m
- Joists
- New · horizontal · 300 mm centres
- Board angle
- Straight
- Board wastage
- 10%
- Edging
- No edging
- Open edges with fascia
- 0
Started on your phone? Save this address so you can finish the design on a laptop or desktop:
Send for a quote
Keep the editable design file on your device. Return and choose “Open design” to continue measuring or make changes.
Substructure & Decking Coverage Plan
Sylvan Deck Designer
sylvan-decking-design-app.lovable.app
Design date 28 October 2026
Design ref —
28 October 2026
Customer details
- Name
- —
- —
- Phone
- —
- Customer postcode
- —
Section 1 — Substructure plan
Shape
Rectangle / square — 6m length, 4m width
Board
Hollow Board — Anthracite — Wood-grain finish
Substructure area
24.00 m²
Perimeter
20.00 m
Joists
New · horizontal · 300 mm
Site plan — boundaries & joist layout
ALength: 6.00 mBWidth: 4.00 m
Joists run horizontal at 300 mm centres. Hatched edges butt up to a wall / structure. Boards are not shown — see board direction key.
Board direction key
Boards run vertical
Indicative only — boards run across the joists. Board layout is confirmed at the decking design stage.
Edge schedule
| Side | Edge | Length | Condition |
|---|---|---|---|
| A | Back edge | 6.00 m | Open |
| B | Right edge | 4.00 m | Open |
| C | Front edge | 6.00 m | Open |
| D | Left edge | 4.00 m | Open |
| Total perimeter | 20.00 m | 0.00 m against structure | |
Section 2 — Decking coverage
Coverage summary
- Coverage area
- 24.00 m²
- Fascia / skirt board
- None
- Board direction
- Vertical (across joists)
- Board basis
- 4.00 m × 150 mm
- Board
- Hollow Board — Anthracite — Wood-grain finish
- Installation temperature
- Below 25°C
Coverage area includes the substructure frame plus any fascia / skirt board on open edges. Any board overhang is decided later in the edging section. The fascia adds 25 mm per selected edge to the finished decking footprint.
Design document — not a detailed construction drawing. All setting out must be measured and checked on site against the full Installation Guide. Minimum board piece used: 600 mm; maximum unsupported span: 400 mm.
Section 3 — Decking plan
- Board angle
- Straight (0°)
- Joist centres
- 300 mm (new)
- Unsupported board span
- 300 mm — within 400 mm limit
- End-to-end butt joints
- Set out on site
- Board
- Hollow Board — Anthracite — Wood-grain finish
- Installation temperature
- Below 25°C
Spacing requirements
Perimeter clearance
0 mm to walls / structures
Side to side gap
7 mm (7 mm spacing block)
End to End Board Gap allowance
12 mm
End to fixed object
12 mm
Gaps shown are for the installation temperature selected above. Every end-to-end joint must be supported by a joist or a noggin.
Decking Plan before Edging
Pre-plan — spacings shown are the installation allowances. Joint positions are set out on site. Indicative only, all setting out must be measured on site.
Decking plan — boards run vertical (straight). Orange dashed line shows fascia / skirt board on open edges.
Started this design on your phone? Open sylvan-decking-design-app.lovable.app on a laptop or desktop to keep going — your measurements are on this plan.
Substructure and decking coverage plan only, based on the dimensions entered. Construction must follow the full Sylvan Composite Decking Installation Guide and current building regulations.
Approved by / date