Last updated: January 2025

Decking Cost Estimation: Budget Guide for Garden Decks

Understanding the full cost of a decking project before you start is essential for staying on budget. The price of decking boards is only part of the story — you also need joists, bearers, posts, screws, weed membrane, and potentially railing. Then there are the tools, site preparation, and disposal costs that many budget guides overlook. This comprehensive guide breaks down every cost component so you can plan your project with confidence, whether you are building a small patio platform or an expansive garden entertainment area.

Material Costs Breakdown

Decking board prices in the UK vary enormously depending on material choice. Pressure-treated softwood is the most budget-friendly option at £4–6 per linear metre, making it accessible for most garden projects. Hardwood species like oak, iroko, or cumaru range from £10–18 per metre but offer superior durability and a richer appearance. Standard composite boards cost £15–22 per metre, while premium capped composite ranges from £22–35 per metre for top-tier brands.

Joist timber (47mm × 150mm treated softwood) typically costs £3–5 per linear metre. You will need approximately one joist per 450mm of deck length, each spanning the full deck width. Bearer timber is slightly more expensive at £5–7 per metre for the larger 47mm × 200mm sections commonly used. Posts cost £8–15 each depending on height and material.

Fixings add up more than most people expect. Stainless steel decking screws cost £15–25 per box of 200, and a typical 12m² deck uses 400–600 screws (2–3 boxes). Joist brackets, post brackets, and bolts add another £30–50. Weed membrane (£1.50–2.50 per m²) is essential under the deck to suppress plant growth. The calculator totals all of these automatically.

Cost by Deck Size

To give you a rough benchmark, here are typical material costs for common deck sizes using treated softwood with a standard layout (excluding labour):

• 3m × 3m (9m²): £350–500 — a compact patio deck suitable for a bistro table and two chairs. See our 3×3m worked example for a detailed breakdown.
• 4m × 3m (12m²): £450–650 — a popular medium size that accommodates a dining table and chairs.
• 5m × 3m (15m²): £550–800 — enough for separate dining and lounging zones.
• 6m × 4m (24m²): £800–1,200 — a large entertainment deck. Composite at this size costs £1,800–3,000 in boards alone. See our 6×4m composite example.

Hidden Costs to Budget For

Several costs catch first-time deck builders by surprise. Site preparation — removing turf, levelling ground, and compacting soil — can take a full day and may require hiring a mini digger (£100–150 per day) for larger areas. Skip hire for waste disposal costs £200–350. If you need to remove an existing deck, add another day's work and skip space.

Tool costs can be significant if you do not already own the basics: a mitre saw (£80–200), drill driver (£50–100), impact driver (£60–120), spirit level (£15–30), and tape measure. Quality tools last for years and are worth the investment, but they should be included in your first-project budget. Consider hiring specialist tools rather than buying if it is a one-off project.

Concrete for post foundations costs around £5–8 per post (postcrete or ready-mix). For a raised deck with 12 posts, that is £60–96 in concrete alone. Stainless steel coach bolts and washers for structural connections add another £20–40 for a typical subframe.

Labour Costs

If you are hiring a professional deck builder, expect to pay £150–250 per day for a skilled carpenter, or £40–60 per square metre installed for a complete deck. A 12m² softwood deck typically takes 2–3 days for a professional to build, costing £400–750 in labour. Composite takes slightly longer due to hidden clip installation, adding 10–15% to labour costs. Complex shapes like L-decks or herringbone patterns can double the labour time compared to a simple rectangle.

Saving Money Without Cutting Corners

The biggest savings come from doing the work yourself. DIY deck building is well within the ability of a competent DIYer with basic tools, and it saves the entire labour cost. Building a deck is one of the most rewarding garden projects because the results are immediately visible and usable. Watch video tutorials, plan carefully, and take your time with the subframe — if the joists are level and square, the rest falls into place.

Other savings: buy boards in full packs rather than individually (bulk discounts of 10–20% are common), choose the board length that creates least waste for your deck dimensions, and consider a standard layout instead of diagonal or herringbone to minimise cutting waste. Compare prices between local timber yards, national chains, and online suppliers — prices vary significantly. Our composite vs timber comparison can help you decide if the premium material is worth it for your situation.

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