Ongoing research by the SPAB is providing convincing evidence to support our long-held contention that the thermal performance (U-value) of old, solid walls is frequently better than assumed and use of ‘breathable’ (‘vapour-open’) insulation minimises the risk of elevated moisture levels that can harm not only traditionally constructed (pre-c1919) buildings but their occupants’ health.

Our findings to date are that standard U-value calculations (used across the construction industry to quantify the rate of heat transmittance through building elements) underestimated the thermal performance of the traditional solid walls sampled in 77% of cases. In some instances, heat loss was up to three times lower than calculated. Ultimately, this could have negative consequences for old buildings because the adoption of overly pessimistic theoretical U-values as the baseline for assessing the thermal performance of their walls may lead to disproportionate energy saving interventions that are not only unnecessary but also invasive and potentially harmful to historic fabric.

Our research suggests that the performance of solid walls after insulation is affected not only by the external and internal climate but material characteristics (such as vapour permeability), quantity of insulation, location, orientation and condition. It suggests that excessive thicknesses of insulation and non-breathable materials should be avoided. It also shows, though, that uninsulated solid walls tend to lose less heat than previously thought and that thinner installations of less high performing, more breathable insulation – where insulating is justified – can achieve successful upgrades.

Download the SPAB Research Reports:

SPAB Research into the Energy Efficiency of Old Buildings: A Precis

The SPAB Research Report 1: U-value Report. Revised November 2012

The SPAB Research Report 2: The SPAB Building Performance Survey:
Interim Report, October 2011
Interim Report, October 2012
Interim Report, October 2013
Interim Report, December 2014
Interim Report, October 2015
Interim Report 2016 (published February 2017)
Interim Report, December 2017

Final Report, December 2019

Building Performance Survey 2016 – Summary

The SPAB Research Report 3: Hygrothermal Modelling: Interim Report. October 2012