Building regulations make allowances for existing buildings when it comes to improving thermal performance. It’s called design flexibility. Yet when it comes to extensive refurbishments and extensions we have to tread carefully.
External wall insulation can become a singular focus in properties where an exterior wall has been stripped right back to the bare brick.
In a recent project in London the building control officer was not satisfied with building regulations notional and proposed SAP calculations. They simply demonstrated the improvement of thermal performance for the building as a whole based on some original u-values from the existing house.
The building control officer was worried about the stripped external wall and why it couldn’t have all the insulation required to meet building regulations minimum standard? The reason was simple, not enough space and external insulation wasn’t an option.
So, seeking a solution, the building control officer asked for a set of notional SAP calcs where every elemental u-value was at current building regulation minimum standard. This had to be accompanied by the proposed set of SAP calculations with the u-values proposed by the developer. This included some compensation of extra insulation in the ground floor and roof with a low u-value for windows too.
This proved acceptable because the difference between the two dwelling emission rates showed a better level of energy efficiency in the proposed dwelling despite the slightly underperforming external wall.
Food for thought.