I'm Alfie Jaques, a City & Guilds-qualified carpenter based in Bournemouth (BH2), and I build decks and pergolas across Poole, Christchurch and about 10 miles around. Every quote I give is written and itemised after a free visit to the garden.
A raised deck is often the only way to get a flat, usable space on a garden that falls away from the house, and plenty of gardens here do. It's also where the rules start to bite. This guide covers why so many local gardens slope, the height lines that matter for planning and Building Regulations, and what goes underneath to hold it all up.
Why do so many Bournemouth gardens need a raised deck?
Because a lot of them step down a slope, especially near the chines and cliff tops.
BCP Council describes a chine as "a steep-sided dry river valley", and Bournemouth has several running down to the sea, Alum, Middle, Durley and Boscombe among them. Gardens along their sides, and along the West Cliff and East Cliff frontage, often drop away from the back door. A raised deck is often the most practical way to get a level surface there: the posts follow the ground down and the deck stays flat on top.
When does a raised deck need planning permission?
When it's more than 30cm above the ground. On a slope, check where that's measured from before you design it.
The Planning Portal says decking is permitted development only if it is "no more than 30cm above the ground", covers no more than half the garden together with other extensions and outbuildings, and none of it sits forward of the front wall of the house. Those rules apply to houses, not flats or maisonettes, and within the grounds of a listed building no decking is permitted without an application.
On a slope that 30cm catches people out. A deck that's flush with the patio at one end can be well above the ground where the garden falls away. The government's guidance takes height from the highest ground next to a structure, but it doesn't say how that applies to a deck on a slope, so if any part will be more than 30cm above the ground beneath it, get BCP Council's view in writing, or a lawful development certificate, before you build. My page on decks over 30cm goes through the measuring question, and the decking planning permission guide covers conservation areas and flats.
Does a raised deck need Building Regulations approval?
If it needs planning permission, assume it does.
The Planning Portal's own wording is that "Building Regulations should be assumed to apply to every deck structure requiring planning permission." In practice that means the frame, footings and any edge protection get looked at by Building Control, which for most addresses I cover is BCP Council.
That's worth knowing at the start, because it affects the design, the timeline and the paperwork as well as the build, and it's part of what decides the price of a new deck.
When does a raised deck need a balustrade?
The government's guidance on falls in homes kicks in at a drop of more than 600mm.
Approved Document K is the government's guidance on protection from falling. For homes, it says guarding should stop people being "injured by falling from a height of more than 600mm". Its table of guarding heights for single-family dwellings gives 900mm for stairs, landings and the edges of internal floors, and 1100mm for "external balconies" and the edges of roofs.
Where young children will use the space, the same document says no gap in the guarding should let a 100mm sphere through, and that horizontal rails should be avoided so it isn't easy to climb.
A raised garden deck isn't named in that table by itself, so which height applies to your deck is one to confirm with Building Control. I check it before the design is fixed.
What holds up a raised deck on a slope?
Posts on footings that go down into solid ground, set out to follow the fall of the garden.
Each post carries more load, and over a longer length, than on a low deck, so what sits under it matters more. The ground here varies sharply: the British Geological Survey describes the cliffs as weak sandstones and mudstones from the Boscombe Sand and Branksome Sand formations, with sand and clay side by side, and records a landslide on a section of East Cliff on 24 April 2016. Gardens near the cliff edge need the ground looked at properly before anything is designed.
Inland, the same sand-and-clay mix shows up in back gardens, which is why I check the ground at your address rather than assume it from the postcode. The frame and posts are Use Class 4 treated timber, the standard for timber in the ground or kept wet, and I cut the joints into the frame instead of relying on screws and brackets alone. See decking on clay soil for how moving ground is dealt with, and which decking screws last near the sea if your slope faces the coast.
What about steps and getting on and off the deck?
Plan them in from the start, especially if older family members will use it.
Steps down from a raised deck are part of the structure, and Approved Document K asks for guarding at the sides of flights of steps where there's a drop of more than 600mm. It's also worth planning the steps, and a handrail, around whoever will use them most, whether that's small children or older family members.