Energy efficiency is becoming the key issue for people working with historic buildings. SPAB believes that if approaches aren't based on the right figures to begin with, then we could, unintentionally, be doing untold, invasive damage.The initial objective of the SPAB research project was to fit in with the work begun by Historic Scotland and Historic England. Historic Scotland has produced a various reports , looking mainly at the performance of sandstone construction, while English Heritage is currently looking at brick construction. SPAB felt a responsibility to represent other nationally important traditional walling types such as, wattle & daub paneling, cob, limestone, slate, granite etc. These traditional materials often get overlooked, but, from a historical perspective, they probably have the most to lose in terms of standard assessment.

Results from the first stage of SPAB's 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. In some instances, it now appears that heat loss through vernacular materials can be up to three times lower than expected.

The initial 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 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, formerly 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 base-line for assessing thermal performance of different types of constructions. However, SPAB's on-the-spot research suggests that 77% of the traditionally built walls sampled (including walls of timber, cob, limestone, slate, and granite) actually perform better than expected.

Jonathan Garlick, SPAB technical officer explains: "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. 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. 

Jonathan Garlick says: "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."

For more information, download our research reports, visit Historic Scotland's Technical Conservation Knowledge Base or read the SPAB Briefing on energy efficiency.