If you are pricing up a conservatory, the base is often the first thing on your mind and the first thing quoted. The good news is that in most cases the base itself does not need its own planning permission, because planners look at the whole conservatory, not the slab underneath it. There are exceptions though, and in parts of Bristol they catch people out.
Planning law does not treat a conservatory base as a standalone project. When a council assesses whether you need permission, it considers the finished structure: its footprint, height, position on the plot and how much of your garden it covers. The concrete slab or dwarf walls beneath it are simply part of that structure.
So the real question is whether the conservatory itself needs permission. Most do not, because they fall under permitted development rights, which allow single storey rear extensions without a planning application provided they stay within set limits.
For most houses in England, a conservatory can be built without planning permission if it meets all of the following conditions. Miss any one of them and you will need to apply, base and all.
Bristol has more than 30 conservation areas, including Clifton, Redland, Montpelier, St Andrews and much of Bedminster around the Chessels. In a conservation area permitted development still applies to rear conservatories in most cases, but side extensions and anything visible from the street are treated more strictly, and some streets have Article 4 directions that remove permitted development rights altogether.
If your home is listed, you will need listed building consent for a conservatory regardless of size, and that includes groundworks for the base. It is also worth knowing that once the base goes in, you are committed, so a quick check on Bristol City Council's planning pages or a free call to their duty planner before excavation is time well spent. A lawful development certificate costs around £150 and gives you written proof the work was permitted, which is useful when you sell.
Even where no planning permission is needed, the base can still matter for building regulations. A conservatory is exempt from building regs if it is under 30 square metres, built at ground level, thermally separated from the house by external quality doors, and has its own heating controls. Most standard installations qualify.
If you later remove the doors between house and conservatory, or fit one large enough to need approval, the base will be inspected like any other foundation. That means adequate depth, typically 600mm to 1 metre depending on ground conditions, and deeper near trees or on the shrinkable clay found across parts of south and east Bristol. A properly built base with a damp proof membrane and insulation costs little more at the outset and avoids expensive remedial work if you ever upgrade the conservatory to a full extension.
No separate permission exists for a base alone, but laying one counts as starting the development. If the finished conservatory would need permission, you should have it granted before any groundwork begins.
Typically 600mm to 1 metre of foundation depth, with the final figure depending on soil type and nearby trees. On the clay soils common in parts of Bristol, or within a few metres of a mature tree, deeper foundations are often needed.
Not necessarily. Permitted development limits depend on your specific house, plot and any previous extensions, and some Bristol streets have had those rights removed. Check your own position rather than relying on what worked next door.
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