Planning Your Decking Project
Before ordering materials, decide on the deck size, shape and height above ground level. Most domestic decks in the UK do not require planning permission provided they are no more than 30 centimetres above ground level and do not cover more than 50 per cent of the garden area. However, if your property is listed or in a conservation area, you should check with your local planning authority first. The subframe, typically built from treated timber joists at 400-millimetre centres, must be properly supported on concrete pads or adjustable pedestals to ensure a level, stable surface.
Deck boards are usually 140 to 150 millimetres wide and come in lengths of 2.4 to 4.8 metres. Planning your board layout in advance helps minimise cuts and waste. Running boards parallel to the longest dimension of the deck generally looks best and reduces the number of end joints needed. If your design includes diagonal or herringbone patterns, allow an extra 15 to 20 per cent for waste.
Comparing Decking Materials
Pressure-treated softwood is the most affordable option, typically costing 3 to 6 pounds per metre. It requires annual treatment with decking oil or stain to maintain its appearance and prevent rot. Hardwood decking, such as balau or iroko, costs more at 8 to 15 pounds per metre but is naturally more durable and requires less maintenance. Composite decking, made from a blend of wood fibres and plastic, costs 10 to 25 pounds per metre but is virtually maintenance-free, splinter-free and does not rot, making it popular despite the higher upfront investment.
Maintaining Your Deck
A well-maintained timber deck can last 15 to 25 years. Clean it at least once a year with a suitable deck cleaner and a stiff brush to remove algae, moss and dirt that make the surface slippery. Apply a decking oil or stain annually to protect the wood from UV damage and moisture penetration. Check fixings and the subframe periodically for signs of movement, corrosion or rot, replacing any compromised components promptly.
For related garden projects, try our fence calculator or gravel calculator. For planning permission rules and permitted development rights, visit GOV.UK.
This calculator provides estimates for guidance only. Results are based on the figures you enter and typical UK averages. This is not professional, financial, medical or legal advice. Always consult a qualified professional for specific guidance.