Key takeaways
- Many rear conservatories fall under permitted development and need no planning application, within size limits.
- As a guide, a rear conservatory can extend up to 4 metres on a detached house or 3 metres on a semi or terrace, under 4 metres high.
- Your allowance is cumulative: extensions a previous owner added count against what you can build now.
- Listed buildings, conservation areas and flats have tighter rules, so always check with your council first.
A conservatory often counts as permitted development, which means no full planning application, but only if it stays within set limits. Go beyond them and you will need permission. Here is how to tell which side of the line you are on.
When you usually do not need permission
A conservatory built at the rear is normally permitted development if it does not extend more than 4 metres from the rear wall on a detached house, or 3 metres on a semi-detached or terraced house. It must be no more than 4 metres high, and where it sits within 2 metres of a boundary the eaves must not exceed 3 metres. It also must not cover more than half the garden, and must not project forward of the front of the house.
When you do need permission
You will need to apply if the conservatory goes beyond those limits, faces a road at the front, or sits on a flat or maisonette rather than a house. Listed buildings, conservation areas and other designated land have stricter rules, and permitted development rights are sometimes removed altogether.
The catch: the allowance counts every extension the house has ever had. If a previous owner already added a rear extension, you may have little or none of your permitted development left, even though you have never built anything yourself.
Larger conservatories
Bigger single-storey rear extensions, up to 6 metres on a semi or terrace and 8 metres on a detached house, can sometimes go ahead under a prior approval process. You notify the council, they consult your immediate neighbours, and if no one objects on valid grounds it can proceed. It is not automatic, so allow time for it.
Building regulations
Separate from planning, a conservatory is often exempt from building regulations if it is at ground level, under 30 square metres, separated from the house by external doors or windows, has its own heating controls, and uses safety glazing. Change any of those and the regulations can apply. For costs and value, see our home improvement cost report and improvements that add the most value.
FAQ
How big can a conservatory be without planning permission?
As a guide, up to 4 metres deep on a detached house or 3 metres on a semi or terrace, under 4 metres high and covering less than half the garden. Previous extensions count against this, so check your remaining allowance.
Does a conservatory need building regulations approval?
Often not, if it is under 30 square metres, at ground level, thermally separated from the house and uses safety glazing. If it does not meet those conditions, building regulations can apply.
What about conservation areas and listed buildings?
Rules are tighter, and permitted development rights may be restricted or removed. Always check with your local planning authority before starting in these cases.