Planning decking, fencing and a shed base

Decks, fences and sheds are all timber on a base, and the base decides how long they last. Posts in the ground, joists on supports and a shed on a slab or a pad all need to be level, solid and clear of damp. The rules differ from the patio: height limits for decking and fences, and distances from boundaries for outbuildings.

This planner covers the rules first, then the three jobs. Skip to the one you need.

Step 1: Check the rules

Under permitted development in England, decking more than 30 cm above the ground needs planning permission, a fence is limited to 2 m (1 m next to a highway), and outbuildings have limits on height and on how much of the garden they cover. Conservation areas, listed buildings and some homes have stricter rules. Check with your council.

Step 2: Decking: frame and boards

Decking sits on a frame of joists on supports on a level, well-drained base with a weed membrane. Joists are usually at 400 mm centres, or closer for thin boards. Leave a gap between boards for drainage and expansion, and a ventilated space under the frame.

Step 3: Fencing: posts, concrete and panels

Posts are set in holes with concrete or fast-setting post mix, about a third of the post length down, with the panels between them. Standard panels are 1.83 m (6 ft) wide, so the posts are about 1.8 m apart centre to centre. Concrete spurs or gravel boards keep the wood off the ground.

Step 4: A base for a shed

A shed needs a level, firm base that is slightly larger than it, either a paving-slab base on compacted stone, a concrete slab, or a timber frame on piers. Keep the floor off the ground to avoid damp. Check the shed maker's instructions for the base size.

Step 5: Finish and protect the timber

Treat or stain timber when it is dry, and treat cut ends. Check bolts and fixings for rust after the first winter.

Before you start

• Planning permission or permitted development limits for height and position.
• Where the boundary is, and a conversation with the neighbour before you build a fence.
• Services in the ground, before you dig post holes.
• Dry timber, stored flat and off the ground.
• Galvanised or stainless fixings for outdoor use.

Mistakes that cost people money

• Building decking more than 30 cm high without permission.
• Setting fence posts directly in soil, or too shallow, so the fence leans.
• A shed base that is not level or too small.
• Decking boards laid with no gap or no airflow beneath.
• Using interior screws that rust and stain the wood.

Frequently asked questions