What are the rear depth limits for permitted development?

For semi-detached and terraced houses, the maximum rear extension depth is 3m (or 6m with prior notification under the larger home extension scheme). For detached houses, the limits are 4m (or 8m with prior notification). These are measured from the original rear wall of the house. Conservation areas cannot use the larger extension scheme.

What is the larger home extension scheme (prior notification)?

The larger home extension scheme allows deeper single-storey rear extensions under PD — up to 6m for semi/terraced and 8m for detached — subject to a prior notification process. You submit a notification to the council, who consult your neighbours. If no objections are raised within 42 days, you can proceed. This does not apply in conservation areas.

What height limits apply to PD extensions?

Extension eaves must not exceed 3m. The ridge of a rear extension must not be higher than the existing house ridge. For side extensions, eaves are limited to 3m and only single storey is allowed under PD. The extension must not be higher than the highest part of the existing roof.

Can I extend in a conservation area under PD?

PD rights are more restricted in conservation areas. Rear extensions are limited to 3m (semi/terraced) or 4m (detached) — the larger extension scheme does not apply. Side extensions and cladding are not permitted. Any extension visible from a highway may require planning permission. Always check with your local authority.

Do I still need Building Regulations for a PD extension?

Yes. Permitted Development only removes the need for planning permission — it does not affect Building Regulations. All extensions must comply with Building Regulations (structure, insulation, ventilation, drainage, fire safety, electrics) and require a Building Regulations application and inspections.

TradeCalculator

Extension Permitted Development Calculator — PD Rights Check

Check whether your extension falls within permitted development rights based on rear depth limits, eaves height, ridge height and property type.

House type

Extension position

Rear extension depth

Extension eaves height

Extension ridge height

Existing house ridge height

How We Calculate This

This calculator checks your extension dimensions against the permitted development rules set out in the Town and Country Planning (General Permitted Development) Order 2015 (as amended).

Key PD limits

Rear depth: 3m semi/terraced, 4m detached (or 6m/8m with prior notification)
Eaves height: maximum 3m
Ridge: must not exceed existing house ridge height
Side extensions: single storey only, not in conservation areas

Frequently Asked Questions

Related Calculators

Extension Cost Estimator

Estimate extension cost per m² for single and two storey with material breakdown.

Extension Foundation Calculator

Calculate extension foundation depth and width with tree proximity per NHBC Table 4.2.

Extension Roof Calculator

Calculate extension roof materials for pitched or flat with insulation.

Extension Wall Calculator

Calculate extension wall materials: blocks, insulation, bricks, DPC and wall ties.

Garage Conversion Calculator

Calculate garage conversion insulation, replacement door structure and services.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.