25% rennovation rule

[garyo]

How is the "25% renovation of any thermal element" rule applied to knock through extensions?

Specifically - Let's say I built a single storey rear extension on the back of a house, and knock the entire wall through so that the size of the original room in the house - let's call it a lounge - was doubled. It would look like one large room apart from a couple of piers and a downstand where an RSJ must be.

Have I renovated 50% of that room, so need to bring the floor and wall insulation up to spec in the existing half of the room?

Gary

 

[jeds]

Have I renovated 50% of that room, so need to bring the floor and wall insulation up to spec in the existing half of the room?
Gary

No, because you have not renovated or replaced 25% of a thermal element. If you were to hack off 25% of the plaster or lift 25% of the floor in the original room then technically that would need to be upgraded.