Whats an outbuilding conversion deemed as

[livingthedream]

Does anyone have any experience to what an extension and conversion of a car port into a fully enclosed annex be deemed as a "new dwelling" or in the eyes of U-values "fabric elements of existing dwellings"?

[Temp]

I believe it's the latter unless planning permission allows the annex to be sold off as a separate dwelling.

[kandgmitchell]

Table 4.2 of Approved Document L Volume 1 - Dwellings - it's an existing building.

 

However, if the annexe is to be a separate dwelling then refer to paragraph 11.5 of that document, because that is a change of use, in which case new elements should still comply with table 4.2 but existing elements need to be brought up to comply with Table 4.3.

[DevilDamo]

It would be based on upgrading retained thermal elements, similarly to a garage conversion.