House extension - Insulating existing concrete floors

[akist]

We are building an extension and the building control surveyor said that even for extension a certain U value must be achieved for all the retained structures (walls and floors), and from a table he sent to me for the floor, it is 0.70 as a minimum (threshold) with 0.25 listed as "improved".

I am slightly puzzled and concerned because I have visited various extension projects and the do not insulate any retained walls or ground floors, only the new parts. Insulating an existing floor means breaking up the existing, in which case it is not an "extension"?

Can anyone please help me with this?

 

[Notch7]

Do you mean you are building an extension, but some of the new room is utilising some existing parts?

In which case you should improve.

It would be in your interest to have better floor insulation anyway.

 

[DevilDamo]

New thermal elements would need to meet the u-values as stated in L1B (Table 2) and retained thermal elements (that are usually subject to those areas being converted or upgraded) would need to meet the u-values as stated in L1B (Table 3).

 

[^woody^]

Only the new bits need to meet current standards, not the existing bits - unless you are converting existing rooms.