What Are The Rules On House Extensions

What are the rules on house extensions?

Heather

Written by

Heather

Last updated Tuesday 6th October 2020

Dovercourt road 4 large

We won’t lie to you, there are quite a few rules when it comes to building an extension, but this doesn’t have to put you off. Like any game, once you know the rules, you’re more likely to score and win yourself that extension you’ve been dreaming of.

In this quick guide, we'll be discussing the rules around permitted development rights. This is the easiest way to add an extension on your home, as you won’t require full planning permission. It's also the planning route with the most defined rules, as a full planning application is more subjective and dependant on the area you live in.

Now we’ve got that out of the way, let’s start from the ground up. Here are a few areas that you need to consider...

Rules for a rear extension

Your project must...

  • Sit to the rear of the house (not the front)
  • Not extend beyond the rear wall of the existing house by 3m if an attached house or 4m if detached
  • Use similar building materials to the existing house
  • Take up less than 50% of the size of the land around the original house ("original" being the latest of when the property was built or if it was built before 1948, then as it stood on 1st July 1948)
  • Be less than 4m in height (or less than 3m if within 2m of a property boundary)
  • Have eaves and a ridge that are no taller than the existing house

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Rules for a two-storey extension

Your project must...

  • Have no windows in wall/roof slope of side elevation in additional storeys
  • Take up less than 50% of the width of the original house
  • Take up less than 50% of the size of the land around the original house ("original" being the latest of when the property was built or if it was built before 1948, then as it stood on 1st July 1948)
  • Use similar building materials to the existing house
  • Have eaves and a ridge that are no taller than the existing house
  • Terraces to be no more than 3.5m higher than the next tallest terrace.

Single storey homes are excluded.

Rules for a side extension

Your project must...

  • Sit to the side (as long as this will not face a highway) of the house (not the front)
  • Use similar building materials to the existing house
  • Take up less than 50% of the size of the land around the original house ("original" being the latest of when the property was built or if it was built before 1948, then as it stood on 1st July 1948)
  • Take up less than 50% of the width of the original house
  • Be less than 4m in height (or less than 3m if within 2m of a property boundary)
  • Have eaves and a ridge that are no taller than the existing house

116 Roakes Avenue 4

Rules for a wraparound extension

When combining a side and rear extension to form a ‘wraparound’, the permitted development restrictions will be judged against the criteria for both extensions individually, making it unlikely for the project to fall under your permitted development rights. For instance, side extensions are only permitted development where they are less than half the width of the original dwelling, but the combination of a side and rear extension will likely exceed half the width of the original.

Rules for loft extensions

When converting your loft, your project must...

  • Have a volume allowance of 50 cubic metres additional roof space for detached and semi-detached houses
  • Use similar building materials to the existing house
  • The development must not include a window in any wall or roof slope forming a side elevation of the dwelling house
  • The roof pitch of the principal part of the dwelling must be the same as the roof pitch of the existing house
  • Have a dormer wall that is set back at least 20cm from the existing wall face
  • Have windows that are non-opening if less than 1.7m from the floor level
  • Have side windows that are obscured/frosted

Homes where different rules apply

The following property types don't benefit from permitted development rights and will need to use a full planning application...

  • Listed buildings
  • Flats or maisonettes
  • Some new developments

Homes from conservation areas are not excluded from permitted development rights, however they do hold much greater restrictions.

It's also worth noting, certain homes and areas have not been included in the 2020 extension of permitted development rights. These are...

  • Homes within Scotland, Wales, or Northern Ireland
  • Homes built before 1948

In these cases, you'll still be able to enjoy having permitted development rights but you'll need a full planning application if you want to add a new storey or build a larger rear extension.

If you are unsure of what rules apply to your home, we recommend seeking tailored advice from our experts. Book a free consultation with them here.

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