The three planning measurements
A porch outside an external door can normally use Class D permitted development where its ground floor area, measured externally, does not exceed 3 square metres. No part may be more than 3 metres above ground level. No part may be within 2 metres of a boundary between the dwellinghouse's curtilage and a highway.
These tests apply together. The 3 square metre figure is not usable internal floor space: enclosing walls consume some of that footprint. Likewise, the height test concerns the highest part, not simply the eaves. The Planning Portal porch rules describe these national limits.
Measure the highway relationship accurately
The relevant distance is to the curtilage boundary with the highway, not just the road's carriageway. A pavement or public highway verge may place that boundary closer than the visible traffic lane. Corner plots can have more than one highway-facing boundary, so checking only the front garden depth may miss a restriction.
Show the closest part of the proposed porch on a measured site plan, including relevant projections. Do not assume a hedge marks the legal highway extent. Where ownership or highway limits are unclear, seek appropriate records before designing tightly to the minimum distance.
Check eligibility and other consents
These porch rights apply to eligible houses, not flats or maisonettes, and certain homes created through permitted development routes are excluded. Planning conditions or an Article 4 direction may remove the entitlement. A porch can serve a side or rear external door; it is not restricted to the main front entrance.
Listed building consent may be required where work affects a listed building's special interest, even if a planning allowance appears available. Conservation area status does not by itself remove every porch right, but local restrictions still need checking. Read the wider permitted development explanation alongside the property's planning history.
House extension plans
- Single storey rear extensions, including open plan kitchen and family rooms
- Side return and infill extensions on terraced and semi-detached houses
- Wraparound extensions combining a side and rear addition
The separate building regulations exemption
A ground-level porch with a floor area below 30 square metres is normally exempt from building regulations where the existing external entrance door remains in place. The glazing and any fixed electrical installation must comply with the applicable requirements. Where the house has ramped or level access for disabled people, the porch must not adversely affect that access.
The 30 square metre threshold is not an alternative planning allowance. A porch larger than 3 square metres may require planning permission while still potentially meeting a building regulations exemption. Conversely, a small porch can lose its exemption if the separating external door is removed. Discuss the actual arrangement with building control.
What porch plans should show
Porch plans should identify the external footprint, overall height, roof profile and nearest highway boundary. Include the existing entrance door, proposed door swing, glazing and access levels. Elevations help assess whether the roof and materials sit comfortably with the house, especially where permission is required.
Measured site surveys provide a reliable base where entrance levels or boundaries are awkward. For a porch forming part of wider alterations, house extension plans should show the complete proposal rather than presenting the entrance in isolation.
If the design exceeds a planning limit
Exceeding a Class D limit does not mean a porch is unacceptable; it means that this permitted development route is unavailable. A planning application allows the authority to consider appearance, highway safety, neighbour effects and relevant local policies. A certificate application cannot waive an exceeded dimension.
Avoid reducing the footprint without reviewing usability. Safe entry, suitable glazing, accessible thresholds and room for door movement may be more important than achieving permitted development at all costs.
This guide is general information only and does not replace advice on your specific property. Rules can change, so always check the current position before starting work.
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Frequently asked questions
Is the porch area measured inside or outside the walls?
For the 3 square metre planning limit, measure externally. Internal floor dimensions alone understate the area used by the enclosed porch and its walls.
Can I remove the old front door after enclosing the porch?
Removing the separating external door can take the porch outside the normal building regulations exemption. Obtain building control advice before treating it as part of the heated entrance hall.
Does the highway distance include the pavement?
The test concerns the boundary with the highway, which may include the pavement and verge. It is not simply a measurement to the kerb or carriageway.
Are rear entrance porches covered by the same rules?
Yes. Class D can apply outside any external door of an eligible house, provided the dimensions, highway separation and other relevant restrictions are satisfied.