The short answer
You can build a porch with an external floor area of up to 3m² without planning permission, provided it is also no more than 3m high and more than 2m from any boundary fronting a highway. The 3m² is measured around the outside of the structure, so the usable internal space is a little smaller. As a rough guide, 3m² is around 1.7m by 1.7m, or 2m by 1.5m. Exceed the floor area, the height or the 2m boundary rule and you usually need to apply for planning permission.
Size is the question people ask most about porches, because it sets the limit between a simple permitted-development build and a full planning application. The 3m² floor area is the headline figure, but it only delivers a permission-free porch when the height and boundary conditions are also met. This guide explains exactly how the floor area is measured, what 3m² looks like in practice, and how the three limits work together. The rules summarised here follow the Planning Portal; your local planning authority is the final word for your property.
Porch size at a glance
- Maximum floor area 3m² (external)
- Roughly 1.7m × 1.7m or 2m × 1.5m
- Maximum height 3m
- Distance to highway More than 2m
- Measured Around the outside
- Over any limit Permission usually needed
How the 3m² limit works
The permitted-development floor-area limit for a porch is 3m², measured externally — that is, around the outside face of the walls and glazing. Because the measurement is external, the internal usable area is slightly less once you allow for the wall and frame thickness. The limit applies to the porch on its own; it is separate from the rules that govern extensions. As long as the external footprint is 3m² or less, the floor-area condition is met.
| Example footprint | Floor area | Within 3m²? |
|---|---|---|
| 1.5m × 1.5m | 2.25m² | Yes |
| 1.7m × 1.7m | 2.89m² | Yes |
| 2.0m × 1.5m | 3.0m² | Yes (at the limit) |
| 2.0m × 2.0m | 4.0m² | No — permission needed |
The other two limits matter just as much
A porch within the 3m² floor area is only permitted development if it also satisfies the height and boundary rules:
- Height — no more than 3m from ground level to the highest point. A pitched roof can approach this, so it is worth checking on a taller design.
- Distance to a highway — more than 2m from any boundary fronting a road, public footpath or bridleway. This is the limit that most often catches front porches out.
All three conditions must be met at the same time. See porch permitted development rules for the full detail, and do I need planning permission for a porch for the situations where the rights do not apply at all.
What if you want a bigger porch?
If you want a porch larger than 3m², taller than 3m, or closer than 2m to a highway boundary, you can still build it — you simply apply for planning permission first, and the work will usually also need building regulations sign-off. A larger porch costs more both to build and to get approved, so it is worth weighing the extra space against the added cost and time. See cost to build a porch. This is general guidance, not advice for your specific property; always confirm with your local planning authority and building control.
Sizing your porch? Compare quotes
An FMB-registered or building-control-approved porch builder can design a porch that stays within the 3m² limit and give you an itemised quote. Free to use, no obligation.
Frequently asked questions
What size porch can I build without planning permission?
Up to 3m² external floor area, provided the porch is also no more than 3m high and more than 2m from any boundary fronting a highway. As a rough guide, 3m² is about 1.7m by 1.7m or 2m by 1.5m. Exceed any limit and you usually need planning permission.
Is the 3m² internal or external?
External — the floor area is measured around the outside of the porch. The internal usable space is a little smaller once the wall and frame thickness are taken into account.
Can I build a 4m² porch without permission?
No. A porch with a floor area over 3m² is not permitted development and you would need to apply for planning permission, and it would usually also need building regulations sign-off.
Does a small porch ever still need permission?
Yes. Even a porch under 3m² needs planning permission if it is within 2m of a boundary fronting a highway, is taller than 3m, or your property is a flat, listed building or in a restricted area. Size is only one of the three conditions.
Sources & further reading
- Planning Portal — porches: permitted development floor-area limit
- GOV.UK / Building Regulations Approved Documents — when a porch is exempt
- Your local planning authority / local Building Control — the final word for your property
- Federation of Master Builders (FMB) — finding a registered builder
This is general information, not advice for your specific property. Permitted development rights and their limits can change and can be restricted locally; always confirm with your local planning authority before building. We are an independent information and introduction service, not a builder.