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2nd floor and loft extension


I live in a semi detached and have a single storey rear extension which is 6x4m. We need to build on the existing extension a 2nd floor extension and hopefully a full with dormer loft conversion too. I see in permitted development that the extension can't be higher than 4m. My questions

Is the 4m from ground level or is it the extended part ? (4m doesn't seem that high for an extension)
Can I build the dormer in the loft out to the extended projection from the house (4m)
Would this qualify as permitted development ?

Many Thanks


4 Answers from MyBuilder Architectural Designers

Best Answer

You need planning permission, because it is two storey. You will need Building Control/Structural Engineer to confirm that your existing foundations are suitable for a two storey extension.


Answered 10th Apr 2021

Any second floor extension will need planning permission.
The 4.000m height refers to single storey extensions.
Loft conversions do not need planning permission if you say used Vellux type windows however with a dormer window planning approval would be required.


Answered 10th Apr 2021

The 4 metres threshold refers to the highest point that can be reached by the roof of the ground floor extension, in case of a sloped roof; the reason for this limit is easy to understand: it prevents the roof of the ground floor extension from encroaching with the windows of the first floor.

With regards to the upper floor extension, it DOES require a planning permission; whilst it is still possible to obtain planning consent for 1st floor extensions, these type of extension should be carefully designed in order to avoid a) overdevelopment b) loss of daylight to neighbouring properties, which are usually the grounds for refusal for this kind applications.


Answered 21st Apr 2021

You mention the house is a semi detached house. An additional storey on top of the ground floor extension can only extend out from the original house wall by a maximum of 3 meters under permitted development legislation.
A loft conversion with a dormer is acceptable as long as the total volume created by the new room does not exceed 50 cubic meters. If the extension is within 2 meters of a side boundary then the extension can not be higher than 3 meters.
Hope this helps.


Answered 28th Apr 2021

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