Key Takeaways
- Board Choice: Select Pressure-Treated Softwood for value, Hardwood for longevity, or Composite for low maintenance.
- Subframe Criticality: Use UC4-rated treated timber for joists in contact with the ground to prevent rot.
- Essential Fixings: Use 304 or 316-grade stainless steel screws to avoid corrosion and "bleeding" into the wood.
- The "Gap" Rule: Always leave a 5mm–8mm expansion gap between boards to allow for natural movement and drainage.
- Base Prep: A weed membrane and gravel base are non-negotiable for airflow and preventing vegetation growth.
Lawsons Choices: Decking Essentials Offered
- Board Varieties:Choose from Oxford, Ascot, or Windsor treated timber, or premium composites like Millboard, Trex, and Eva-Last
To build a high-quality deck, you need four primary components: decking boards, UC4-rated structural subframe timber, corrosion-resistant fixings, and a stable ground base. For the subframe, treated joists are the trade standard. When selecting boards, trade professionals increasingly opt for composite for its rot-resistance or slow-grown softwood for a balance of cost and durability. Success depends on using the correct tools—specifically an impact driver for fixings and a mitre saw for clean, square joins—to ensure the structure remains stable and safe under UK weather conditions.
Primary Decking Materials
The longevity of your deck is determined by the quality of the materials selected at the outset.
Decking Board Comparison
- Pressure-Treated Softwood: The most popular choice for ROI. It is easy to work with but requires annual oiling or staining to prevent UV degradation.
- Hardwood (e.g., Oak or Ipe): Offers superior density and natural resistance to decay. Note: These require pre-drilling and specialist stainless steel fixings.
- Composite Decking: A blend of wood fibres and plastic. It does not rot, warp, or splinter. It is ideal for high-traffic areas and requires almost zero maintenance beyond cleaning.
- Anti-Slip Boards: Essential for commercial settings or north-facing gardens that may become damp and slippery.
The Subframe (The "Skeleton")
The subframe is the most common point of failure. We recommend:
- UC4 Treated Joists: Unlike standard treated timber, UC4 is rated for direct soil/ground contact.
- Joist Tape: Applying a waterproof butyl tape to the top of the joists before laying boards prevents moisture from sitting in screw holes, significantly extending the frame's life.
Pro tip: Tape the tops
Apply joist/beam flashing tape before you lay boards — it stops water sitting at fixings and screw holes, which is where rot usually starts.
Essential Tools Checklist
Having the right trade-grade tools ensures precision and safety.
| Tool category | Essential items | Purpose |
|---|---|---|
| Measuring | 8m tape measure, string line, chalk line | Setting out the perimeter and keeping joists/boards true |
| Levelling | 1200mm spirit level, laser level | Keeping the frame level and building in a slight fall for drainage |
| Cutting | Sliding compound mitre saw | Clean, square cuts on boards and joists for tidy joins |
| Fixing | 18V impact driver, combi drill | Driving screws efficiently without stripping heads; drilling pilots |
| Safety | Eye protection, knee pads, dust mask | Protection during cutting, sanding, and handling treated timber |
Pro tip: Sliding mitre saw
Your daily workhorse for clean, square crosscuts and mitres. A sliding saw handles wide deck boards and fascias without tear-out.
Groundwork and Foundation Essentials
A deck is only as stable as the ground beneath it.
- Site Clearing: Remove all turf and vegetation.
- Membrane & Gravel: Lay a heavy-duty weed control fabric and cover with 40mm of clean gravel. This facilitates drainage and prevents "greenery" from growing up through the boards.
- Support Posts/Pads: Use concrete deck blocks or adjustable pedestals to keep the timber subframe off the damp ground. This airflow is critical to prevent joists from rotting from the bottom up.
Pro tip: Deck board spacers + clamps
Use fixed spacers to keep gaps uniform, and decking clamps (or quick-grips) to pull boards tight while you fix — faster installs and straighter runs.
Fixings and Fasteners
Standard wood screws will corrode and snap due to the chemicals in treated timber and natural tannins in hardwood.
- Decking Screws: Use green-coated or stainless steel screws with a "trim head" for a discreet finish.
- Hidden Fasteners: For composite decking, use the manufacturer’s specific clip system to maintain perfect spacing and a screw-free surface.
- Structural Bolts: Use bolts or screws to secure the subframe to the main ledger board or support posts.
Pro tip: Stainless screws
Face-fix with stainless (or approved coated exterior screws) to avoid rust stains and get a longer-lasting hold — especially on hardwoods and wet zones.
Maintenance and Protection
Even "maintenance-free" decks require basic care to stay safe and attractive.
- End-Grain Preservative: Any time you cut a treated joist or board, you must apply an end-grain sealer to maintain the chemical protection.
- Annual Cleaning: Use a dedicated deck cleaner once a year to remove algae and biofilm, which cause the surface to become slippery.
- Oiling: For timber decks, apply a high-quality UV-resistant oil every 12–24 months to prevent the wood from greying and "checking" (splitting).
Frequently Asked Questions
- What is the standard joist spacing?
For most residential decks using 28mm thick softwood boards, joists should be spaced at 400mm centres. If laying boards diagonally or using certain composite brands, this must be reduced to 300mm centres to prevent "bounce."
- How many boards should I order?
Calculate your total square meterage (Length * Width) and add 10% for waste and cutting. It is always better to have two spare boards than to pay for a second delivery mid-project.
- Can I build a deck directly on concrete?
Yes, but you must use adjustable pedestals or rubber "shims" to raise the timber joists slightly. This ensures water can flow underneath and prevents the timber from sitting in standing water.
- Do I need planning permission?
In the UK, you generally don't need permission if the deck is no more than 30cm off the ground and, along with other extensions, covers no more than 50% of the garden area. However, always check local regulations for elevated or "balcony" style decks.
