Old walls perform better
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.
Interesting article. I refurbishing my 17c. cottage after removing all the modern extensions including double glazing the old cottage has become much warmer. The cottage is timber frame, wychert, brick, stone and anything else I think they could find at the time!
Stone most defintely retains temperature better than stick building, properly cured concrete retains energy extremely well. Once Thermal Mass is brought up to temperature it is very difficult to change that temperature, therefore it takes little energy to maintain it. A geo-cell consisting of 1,000,000 lbs. of stone aggregate andf item 4 can be used under the slab to store heat energy collected from a series of 10 geothermal wells, with a basement cooling loop(closed system), or outside water source (open system) to cool the structure during the warmer months. The temperature in the earths soil is 55 degrees. A consistent flow of 55 degree water throughout the radiant tubing coils within the thermal mass panels will bring the structure down to temperature, which is always set at 70 degrees; it is the most comfortable temperature to maintain all year round with no expansion or contraction of the structure. Since it is not a forced air heating system where the temperature of the house will change every time the wind howls because cold air is replacing the forced hot air and the boiler system has to continually start up to heat the house. The thermal mass structure will retain it’s 70 degree temperature with minimal energy applied to the system.
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