For the past year or so I’ve been following some interesting in-situ research by the Society for the Protection of Ancient Buildings (SPAB) about the energy performance of old buildings. Now the results from the first stage of that research are suggesting that standard U-value calculations, used across the construction industry, underestimate the thermal performance of traditional walls. In some cases, it appears that heat loss through vernacular materials can be up to three times lower than expected.
This is quite a revelation because those accepted theoretical performance figures have long been used as a standard base measurement by professionals and homeowners when old buildings are being up-graded, altered or even assessed for Energy Performance Certificates. Put simply, it looks as though the thermal performance of our buildings has been undersold.
Ultimately, this underselling could have negative consequences for historic buildings as calculated theoretical U-values, which suggest a poorer performance, may lead to disproportionate energy saving interventions being adopted which may not only be unnecessary, but also invasive and potentially harmful to the fabric of a building.
SPAB’s research compares the in-situ U-values of various traditional vernacular walls – including timber, cob, limestone, slate and granite – against the theoretical U-value for these walls using the BuildDesk U 3.4 software. It suggests that 79% of the walls sampled perform better than expected.
Of course, U-values are not the complete story. Energy efficiency is also about occupant behaviour in the building, moisture content in the structure, humidity, temperature, air-tightness, the quality of the air we breathe. Even so, this research is a start in broadening our understanding of how old buildings work and I, for one, will watching the ongoing research with interest.
SPAB audio visual presentation on the project here.