Two storey extension

Two storey extension above by Martin, architect on Design for Me. View his full profile and shortlist him for your project here


Do I need planning permission for a two storey extension?

Two storey extensions do not require planning permission, if they fall within permitted development guidelines described below.


How big can I build a two storey extension without planning permission?

  • MAXIMUM HEIGHT: Firstly the eaves and pitch heights must be no higher than those of the existing house. However, if the building is within two metres of a boundary, the overall maximum eaves height is restricted to 3m. The roof pitch should match the existing house as much as reasonable practicable.
  • FOOTPRINT: Under permitted development rules, you can extend up to three metres from the original house* but it must be more than seven metres from the rear boundary (opposite the rear wall). Any extensions to the original house*, sheds or outbuildings should not exceed more than 50% of the total area of land around the house.
  • MATERIALS: The materials used should be similar in appearance to that of the existing house.
  • LOCATION: Two storey extensions to the side or front of the original house are not permitted development.
  • OTHER: No verandas, balconies would be allowed without planning permission. Any upper floor window in a side elevation must be obscured glazing and non-opening (unless its more than 1.7m from floor level internally).

*original house means as it was built or as it stood on 1st July 1948.


There are some specific restrictions regarding your particular property that you will need to check too:

1. Is your property a house?

Flats, maisonettes or any other type of buildings do not have permitted development rights, so you won’t be able to build your extension without getting full planning permission. Also, be aware that if your property has undergone a change of use or has been converted into a house in the past, it may not enjoy permitted development rights.


2. Is your house, or any buildings contained within the boundary, listed?

If so, you will need to contact your local council as other permissions may be required e.g. listed building consent. This often requires more detail than a typical planning application.


3. Is your house in a conservation area or other ‘designated land’

This includes National Parks, areas of Outstanding Natural Beauty, the Norfolk or Suffolk Broads and World Heritage Sites. If so, you will not be able to build your two storey extension without full planning permission.


Note: The above advice relates to England, and policy in Wales may be different.



How much does a double storey extension cost? 


Figures have been updated in 2022 following recent price increases in constructions costs, according to a survey of architects and designers on Design for Me.

As a basic rule of thumb, a two storey extension will cost around 50% more than a single storey extension. Read about extension costs per square metre in our guide here. Based on this guide a (3x6m) two storey extension would be upwards of £60,000 for the basic build cost.

  • Add on 10-15% for professional fees (architect, planning application, building regs, structural engineer) (£6,750 at 15%)
  • VAT (£12,000)

Double storey house extension cost = upwards of £81,000+

Please note this does not include kitchens or bathrooms, and applies to most areas in the UK. Costs in London and SE can be considerably higher.  

For more detail, read our blog on calculating your a house extension cost here.



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