Decking Cost Calculator UK

Decking costs in the UK depend mainly on two choices: the material and whether you fit it yourself. As a guide for fully installed decking including boards, subframe and labour:

Per square metre, installed timber decking typically runs £40 to £110 while composite lands between £100 and £200 for standard boards, rising to £350 per m² for premium capped boards on complex raised structures. If you are comparing boundary solutions, check out our Garden Wall Cost Calculator UK or plan landscaping budgets using the Garden Landscaping Cost Calculator UK.

Decking Board Prices by Material

Board prices vary hugely by species and quality, so this is where your budget decision really sits:

Softwood is the cheapest way onto a deck but needs annual oiling or staining and typically gets replaced within 15 to 20 years. Composite costs more upfront yet resists rot, mold and fading with almost no maintenance, which usually makes it cheaper over 15 years. Hardwood sits in Durability Class 1 with a 40 to 60 year life and no treatment needed.

Subframe, Fixings and Labour

The boards are only part of the bill:

• Subframe: Treated C16 or C24 timber joists, posts and bearers add £15 to £35 per m². You need roughly 7 linear metres of joist per square metre of deck. Joist spacing is 400mm centres for timber boards and 300 to 350mm for composite, which needs the tighter spacing to prevent sagging. Composite or aluminium subframes cost £20 to £40 per m² more but never rot, worth considering when the boards carry a 25 year warranty and a timber frame beneath them may not last that long.
• Fixings: Hidden clips for grooved composite boards add £3 to £6 per m². Stainless steel screws for timber are cheaper but slower to fit neatly.
• Labour: Professional decking installers charge £200 to £400 per day, with London and the South East at the top end. Expect labour to add £80 to £150 per m² on a straightforward ground level deck. Raised decks, steps, balustrades and diagonal board patterns all push labour up and laying boards at 45 degrees uses about 15% more material through extra cuts.

How to Calculate Decking Boards

Measure your deck area in square metres by multiplying length by width. With standard 150mm wide boards and a 5mm drainage gap, you need about 6.5 linear metres of board per m². A 20 m² deck takes roughly 40 boards at 3.6m lengths plus 13 joists at 400mm centres.

Always add 10% for waste and cuts. For L shaped decks, split the shape into two rectangles, calculate each and add them together. Leave the manufacturer's specified expansion gaps with composite, typically 6 to 8mm at board ends, because composite expands with temperature far more than timber. If you are laying concrete pads for structural posts, check the Concrete Calculator UK or plan foundations using the Shed Base Calculator UK.

Planning Permission for Decking

Most garden decking falls under Permitted Development, but a deck raised more than 300mm above ground level needs planning permission. Decking also cannot cover more than 50% of your garden when combined with other outbuildings and extensions. Raised decks that overlook neighbours are the most common trigger for complaints, so check with your local planning authority before building high. If you are comparing overall property extensions, check our Stamp Duty Calculator or evaluate your overall project vat on materials using the VAT Calculator UK.

Ways to Keep Costs Down

Keep the design a straight run, since curves and corners add 15 to 30% to labour time. Choose standard facing bricks or rendered blockwork over reclaimed bricks, which cost 30 to 50% more and waste more in cutting. Clear the site yourself before the carpenter arrives, source timber directly from a merchant to save 5 to 10% and book in autumn or winter when rates soften. If you are calculating soil removal weights, check the Topsoil Calculator UK or estimate overall costs with our home improvement guides.