Top 10 Criteria for Permitted Development

What is Permitted Development?

Permitted Development is a series of policies that describe extensions or alterations to a property that does not require formal Planning Permission. Permitted Development policies exist for any building type or building Use Class. This document discusses Permitted Development for Householders or Dwellings in particular.  

Just build the extension or formalise Permitted Development first?

Basic Permitted Development can be constructed without formalising it through the Local Authority Planning Department. There is a non-mandatory option to formalise the extension or alteration as Permitted Development, which is called a Lawful Development Certificate. Formalising Permitted Development can prove beneficial in clarifying the legality of an extension or alteration, particularly through the resale of the property.

Top 10 Criteria

The following top 10 list gives you a guideline towards understanding the basic policies of Permitted Development for householders:

  1. 50% rule: extensions or outbuildings over and above the original house must not exceed 50% of the curtilage (the land around the original house)
  2. No higher than the highest part of the roof of the existing dwelling house (eaves or ridge)
  3. An extension must not be on the front or principal elevation (one that fronts a highway)
  4. Rear extensions must be no greater than 4.0m for a detached house or 3.0m for any other dwelling type
  5. Extensions must not exceed 4.0m in height
  6. Extensions must not be within 7.0m of any neighbouring boundary to the rear
  7. Side extensions must not exceed half the width of the original house (and not protrude beyond the front or principal elevation)
  8. External materials shall be of similar appearance to the existing dwelling
  9. A loft conversion may be possible, though must not extend beyond the plane of any existing roof slope that forms the principal elevation of a dwelling house and fronts a highway
  10. A loft conversion must be less than 50 cubic meters volume for a detached house and 40 cubic meters for any other dwelling type

The above top 10 criteria are a simple and initial guide to Householder dwelling extension or alteration and do not necessarily form the entire policy information or guidance. Professional advice should be sought for any development either through your Local Authority Planning Department or a professional in the industry, such as an architect or planning consultant.

Where to find advice?

Your Local Authority Planning Department will be able to give you some initial advice towards Permitted Development. They may require some drawings that demonstrate the extent of development in order to provide adequate advice. Your Local Authority Planning Department will offer a Duty Planning officer, either over the phone, by email or at their offices, who can discuss your proposal and advise about Permitted Development.   Please note that fees may apply to obtain advice from the Planning Department.

The Planning Portal is an online website that provides some basic advice towards Permitted Development and other planning-related matters, including an interactive 3D guide.

The actual policies for Householder Permitted Development can be found through this link.

Architects and Planning Consultants are professionally trained to be able to give advice towards Permitted Development.   Professional fees may apply for initial consultations and will certainly apply to engage their services.   However, having professional support in your development will give you the peace of mind that you are meeting your statutory requirements or obligations.


A reasonable degree of development to dwellings is entirely possible through Permitted Development.   Be aware that some local authorities, such as the New Forest National Park Authority, have some additional policies controlling the level of development that may be different from the General Permitted Development Order for Householders.  

Careful consideration should be made when considering an extension to your home and professional advice should be sought to clarify whether the development falls within the Permitted Development Policies.   Where an extension or alteration falls outside any of the criteria set out in the Permitted Development policies it is likely that it will require some form of formal Planning Permission.

Permitted Development, or Planning Permission for that matter, is very different from the Building Regulations.   Both are statutory obligations towards building development.   Your Permitted Development extension or alteration may require separate consent for Building Regulations approval.

As specialists in householder development, V&L architects in Romsey are ideally suited to give advice on extensions & new build house development throughout Hampshire, The New Forest, Salisbury and surrounding areas.   Feel free to give us a call at 01794 524200 or contact us through our website:

Written by Laurence Wright. Laurence is an Architect at V&L Architects, based in Hampshire. He is passionate about improving lifestyle within the residential design and making efficient use of your space.