Some basic rules

Not all decks require planning permission, but check first with your local authority – especially if you are creating raised decks, or bordering a neighbour’s property.

Building regulations may be needed and best practice must be adhered to. As structural stability is vital for raised decks, it is advisable to use a qualified installer. If you are adding a deck to new build, structural calculations may be required.

The Timber Decking Association (TDA) can supply professional and technical information and put you in contact with one of its many members.

Look out for the “Deck Mark” logo – a quality assurance scheme offered by the TDA. This covers the timber components, fixings and finishes, as well as the installed deck  (providing best practice construction methods have been followed).

Site preparation

Plan access for underground services before starting.

Use a weed suppressant membrane, covered with gravel, beneath the deck.

If the deck is adjacent to the house or building, ensure adequate drainage away from the building.

Fixing / products

Ensure the softwood timber used is pressure treated (modern treatments include Osmose Naturewood and Arch Tanalith E).

Give cut ends and drilled surfaces additional treatment with preservative end grain sealer.

Do not allow timber to stand in water before use.

Use corrosion resistant gripper nails. Nails or screws should be twice the length of the timber depth to be fixed.

Use joist hangers, galvanised clips, screws, annular ring nails and “secret fixing” clips to make joining and fixing timber components easier and neater.

Where required, use appropriate concrete foundations with specialist post/shoe holders.

Decking installation principles

Installation

Use timber sections of at least 47mm x 150mm for joists and ledgers.

Fix joists at 400-500mm centres, levelling them from the ledger to the front frame joist, fitting noggins between the joists at appropriate positions to prevent twist and to add stability. Use at least 100mm x 100mm square timber for support posts. Fix the wall ledger 10mm from the brickwork to allow drainage. Avoid bridging the DPC (damp proof course) level.

Stagger joints, ensuring edges butt equally on the joist.

Support raised decks with structural posts set into concrete foundations.

Leave a 6mm gap between boards to allow for swelling and drainage, with a 3mm gap for butt edges.

Pre-drill and countersink screws. Holes should be 2mm oversize for hardwood.

To avoid splits, position fixings 15mm from board ends, sinking nails and screws flush with the deck using a nail punch or countersink bit.

On sloping sites, use multi-levels or cantilevers with calculated supports.

Railings

Building Regulations in England and Wales require 900mm guardrails at lower levels (below 600mm), with 1.1m for decks above 600mm high.

Space newel posts no more than 1.8m apart and spindles no more than 100mm apart.

Fix the bottom rail at least 80mm above the deck.