House Extension: The Secret Sauce of Resale Property Investment

The UK’s resale market of single-home properties has seen increasing popularity recently.  Many of our clients who purchased or looking to purchase such property often ask a question:

Can I expand the size of the house and therefore boost the value of the property?

The quick answer is: YES!  In this blog, we will share some tips on how to plan for and start a house extension!

House Extension in the UK

Based on our experience, most semi-detached and detached residential properties are considered to be a permitted development for an extension. It may or may not require a planning application from local authority. However, it is subject to certain limits and conditions per below:

  • Any part of the extension is not higher than the highest part of the roof of the existing property
  • The eaves of the extension are not higher than the eaves of the existing property
  • Any part of the extension does not extend beyond any wall facing a road if it forms the principal or side elevation of the original property
  • The eaves are no more than 3m in height if any part of the extension is within 2m of the property boundary
  • The materials used in the exterior work are of similar appearance to the existing property
  • An upper floor window on a side elevation within 15m of a boundary with another house is obscure glazed and is non opening unless the parts which can be opened are more than 1.7m above the floor of the room in which the window is installed
  • A side extension does not exceed 4m in height or be wider than half the width of the original property
house extension example
Real client case photo, Aug 2020
Single-storey extension
  • The extension must not extend beyond the rear wall of the original house by more than 4m for a detached house or 3m for any other type of house.
  • The height of the extension must not exceed 4m.
  • No part of the extension is within 3.5m of any property boundary with a road opposite the rear wall of the house.
Extension with more than one storey
  • The extension must not extend beyond the rear wall of the original property by more than 3m.
  • No part of the extension is within 7m of the property boundary opposite the rear wall of the property.
  • The roof pitch of the enlargement is as far as practicable the same as that of the original property.

Before making the decision on property extension, check with the Government’s Planning Guide and investigate the rules and how they apply to what you wish to do. There are two ways to apply for planning permission: It can be completed in writing and submitted to the appropriate authority or it can also be completed online.

If you have any questions about planning, please get in touch with our team. If you are thinking about buying a resale property and make extension at a later time, COSMO can help make that dream a reality. Should you have any other questions about house extension in the UK or overseas property investments in general, feel free to reach out by simply click the live chat button or send us an email to

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