Properties made from traditional stone are more energy efficient than many people think and the thermal performance of such vernacular materials are up to three times lower than expected, a new report shows.
Results from the first stage of the Society for the Protection of Ancient Buildings (SPAB) research on the energy efficiency performance of old buildings suggest that standard U-value calculations used across the construction industry underestimate the thermal performance of traditional walls.
The study suggests that conventional industry practices are struggling to accurately represent the thermal performance of traditionally built walls. Ultimately, this could have negative consequences for historic and older buildings as calculated theoretical U-values (suggesting a poorer performance) may lead owners and professionals to adopt disproportionate energy saving interventions that may not only be unnecessary, but also invasive and potentially harmful to the fabric of a building.
SPAB’s report, written by Dr Caroline Rye, MSc student at the University of Portsmouth, compared the in-situ U-values (U-value is the universally known unit to describe the rate of heat transmittance or loss through a wall / roof / floor etc) of various traditional vernacular walls against the theoretical U-value for these walls using the class-leading BuildDesk U 3.4 software.
Importantly, the theoretical value obtained from the U-value calculations is used by professionals as the baseline for assessing thermal performance of different types of constructions. However, SPAB’s on the spot research suggests that 79% of the traditionally built walls sampled, including walls of timber, cob, limestone, slate, and granite, actually perform better than expected.
Even taking into account a possible error margin of up to 10%, SPAB’s findings show that old buildings may not be as energy inefficient as the building industry has generally understood them to be.
‘Amazingly, this research has not been carried out before in England. 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, but are they correct?’ said Jonathan Garlick, SPAB technical officer.
‘We believe that with some traditional materials our in-situ results prove that they are not. We appear to be actually underselling the thermal performance of our old buildings by not fully understanding them,’ he explained.
‘Energy efficiency is becoming the key issue for people working with historic buildings. If we aren’t basing our approaches on the right figures to begin with, then we could, unintentionally, be doing untold, invasive damage,’ he added.
‘It’s all about understanding the building first, how it performs, how we use it and how we live in it. U-values are not the complete story. Energy efficiency is also about our behaviour in a building, moisture content in the structure, humidity, temperature, air-tightness, the quality of the air we breathe. These are all issues that we intend to consider in further stages of the project.’
SPAB’s energy efficiency project continues throughout 2011. Research is already underway on air tightness, moisture and air quality. Later this year the team will return to buildings constructed from traditional materials that were first assessed in an ‘as found’ state and which have since been upgraded to enhance their energy performance.
‘We believe that this important research will at last reveal some fascinating and useful information to help people make beneficial, effective and appropriate decisions about their old buildings without the need to destroy historical fabric or harm the indoor environment in the process,’ added Garlick.
Roger Curtis, Historic Scotland’s Head of Technical Research added: “We hope that this research will build on our existing knowledge of the thermal performance of traditional building elements and develop our understanding of energy efficiency. In this way we hope to be able to make more sensitive and considered interventions to improve their thermal performance.”