How to Build Decking
Whether you are looking to create a ground-level retreat or a stunning raised deck, building your own decking is a rewarding project that adds significant value and usable space to your home. This guide covers the essential steps for a durable, professional-grade installation.
Key Takeaways
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Foundation is key: Use MOT Type 1 to create a solid, level, and well-draining base for your deck supports.
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Joist spacing: Always maintain a maximum 400mm gap between joists to ensure the deck remains firm underfoot.
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Expansion gaps: Leave a 5-8mm gap between boards to allow for timber movement and drainage.
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Weed control: A quality membrane is essential to stop vegetation growth beneath your structure.
What is a deck base?
A deck base refers to the ground preparation and support structure. Using a compacted sub-base of MOT Type 1 prevents supports from sinking and keeps the area beneath your deck dry and weed-free.
Materials and Tools Checklist
| Category | Items Needed |
| Base | MOT Type 1, Weed control membrane |
| Structure | Treated timber joists, Decking posts, Coach screws |
| Surface | Composite or Timber decking boards, Decking screws |
| Tools | Circular saw, Drill driver, Spirit level, Combination square |
Step-by-Step Installation Guide
1. Site Preparation & Sub-Base
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Excavate: Clear the turf and topsoil to a depth of 100mm.
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Apply Sub-Base: Spread a layer of MOT Type 1 across the area. Compact this thoroughly with a plate compactor to create a rock-solid, level foundation.
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Membrane: Lay a professional-grade weed control fabric over the compacted MOT Type 1 to prevent future growth.
2. Building the Decking Frame
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Outer Frame: Construct the perimeter frame using treated timber joists.
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Inner Joists: Install joists using joist hangers, maintaining a 400mm center-to-center spacing.
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Elevation: If building a raised deck, secure the frame to corner posts using heavy-duty coach screws. Ensure every post is plumb and perfectly level.
3. Laying the Decking Boards
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Start: Lay your first board from one corner, ensuring it is square to the frame.
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Fixing: Drill pilot holes to prevent the wood from splitting. Fasten boards with decking screws, ensuring heads are countersunk.
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Spacing: Use a combination square to maintain consistent 5-8mm expansion gaps between every board.
4. Finishing Touches
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Fascia Boards: Attach fascia boards to the edges of your deck frame for a clean, professional look.
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Safety: Ensure all edges are rounded off. If your deck is raised, install secure railings and non-slip treatments.
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Preservation: If using timber, apply a high-quality deck stain or sealant to protect against weather damage.
Common Mistakes to Avoid
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Ignoring the Base: Building directly on soft soil or grass leads to sinking joists and rot. Always use MOT Type 1 for stability.
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Too Wide Joist Spacing: Anything wider than 400mm will result in “bouncy” or sagging deck boards.
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No Pilot Holes: Skipping pilot holes, especially near the ends of boards, will cause the timber to crack.
FAQs
Can I build decking on top of existing paving?
Yes, but ensure the paving is stable and has adequate drainage. If itâs uneven, use adjustable pedestals to level your frame.
Why is MOT Type 1 better than just sand?
Sand shifts over time and retains moisture. MOT Type 1 compacts into a solid, permeable layer that provides superior structural support for your deck posts.
When should I call a professional?
If your deck is high off the ground (over 600mm) or involves complex multi-level structures, consult a professional to ensure safety and structural compliance.
