Calculation question-Renovation of dwelling with more than 25% of the surface of dwelling envelope?

pathogan2008

I note on my BER Home Energy Upgrade Advisory Report the following:

"1. Major Renovation is defined in the Building Regulations Part L Technical Guidance Document and means the renovation of

a dwelling where more than 25 % of the surface of the dwelling envelope undergoes renovation. Where a dwelling

undergoes a major renovation, the energy performance of the whole dwelling should be improved to the cost optimal level

by achieving a B2 or by implementing the energy performance improvements as set out in the Building Regulations Part L

Technical Guidance Document."

How is 25 % of the surface of the dwelling envelope calculated? What constitutes the envelope? Roof, Walls, Doors, Windows?

Where could I get more information on this?

Thanks

PH

sydthebeat

https://www.boards.ie/discussion/2058312217/calculation-question-renovation-of-dwelling-with-more-than-25-of-the-surface-of-dwelling-envelope

How is 25 % of the surface of the dwelling envelope calculated? What constitutes the envelope? Roof, Walls, Doors, Windows?

Where could I get more information on this?

see TGD L 2021

definitions: major renovations

Major Renovation: means the renovation of a building where more than 25 % of the surface of the building envelope undergoes renovation. 

The surface area of the building thermal envelope means the entire surface area of a building through which it can lose heat to the external environment or the ground, including all heat loss areas of walls, windows, floors and roof.

The surface area should be  calculated as outlined in section 0.4 using internal dimensions. 

essentially, all of the surface area of the dwelling.

sydthebeat

https://www.boards.ie/discussion/comment/121509991#Comment_121509991

any reason you say this?

i must say that i have yet to come across any project where the calculation of the surface area of a dwelling is difficult

muffler

https://www.boards.ie/discussion/comment/121510019#Comment_121510019

From their other comments in multiple forums it seems fairly obvious that they are post building ... or worse maybe!