What can I build? Find out in two minutes.

A careful, indicative check of whether your extension or loft is likely to be permitted development, need prior approval, or need a planning application. It takes about two minutes.

Sheet: P-200
Drawing: Permitted development
Note: Indicative only
Rev: C · Oct 2026

01 Property
02 Restrictions
03 Project
04 Size
05 Result

What kind of property is it?

Property type Detached house Semi-detached Terraced or end of terrace Flat or maisonette

Has the house been extended before? No Yes Not sure

Any special restrictions?

Is it in a conservation area? NoYesNot sure

Is the building listed? NoYesNot sure

Is there an Article 4 direction, or a condition removing permitted development? NoYesNot sure

Your council's website has a conservation area map and Article 4 list. Not sure? Choose "Not sure" and we'll flag it.

What are you planning?

Project type Single-storey rear extension Side or side-return extension Wraparound (side + rear) Loft conversion New basement

Roughly how big?

Depth beyond the original rear wall (m)Enter a depth between 0.5 and 12 m.

Highest point (m)Enter a height between 2 and 8 m.

Is any part within 2 m of a boundary?NoYes

Eaves height near the boundary (m)Enter an eaves height between 1.5 and 6 m.

Width of the side extension (m)Enter a width between 0.5 and 10 m.

Width of the original house (m)Enter a width between 3 and 25 m.

Highest point (m)Enter a height between 2 and 8 m.

Extra roof volume added (m³)A typical rear dormer on a terrace adds 25–40 m³.Enter a volume between 1 and 200 m³.

Does anything face the street (a front dormer)?NoYes

Will the ridge be raised, or is there a balcony or terrace?NoYes

No measurements needed for this one. Wraparounds and new basements are assessed on the next screen.

Please read

This is an indicative guide based on simplified permitted development rules for houses in England (Classes A and B). It is not legal or planning advice.

Permitted development is measured from the original house, and can be removed by earlier conditions, Article 4 directions or local designations. Building Regulations and the Party Wall Act still apply either way.

For certainty, apply for a Lawful Development Certificate, or ask us at a free consultation.

Quick limits (houses)

Rear, attached: 3 m · 6 m with prior approval
Rear, detached: 4 m · 8 m with prior approval
Height: 4 m max · 3 m eaves within 2 m of a boundary
Side: Single storey, up to half the house width
Loft volume: 40 m³ terraced · 50 m³ semi or detached

Sill & StoreyArchitects · Est. 2011

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9 Tranquil Mews
Blackheath, London SE3 0ZZ

Studio open Monday to Friday, 9:00 to 18:00.

020 7946 0418
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Studio & team

Concept design by Orderhatch. Sill & Storey Architects is a fictional business.

Example credentials, shown as plain text only: RIBA Chartered Practice style, ARB-registered architects, professional indemnity insured. Costs are example pricing. Reviews are example reviews. Planning tools are indicative only and are not legal advice. Phone numbers are from the Ofcom drama range.

Concept · fictional business, designed by Orderhatch