There is a long-standing position in the heritage community that insulating masonry walls can present more risks than benefits, but this may not always be the case. Advances in building science, analysis and hygrothermal modelling are bringing a more science-based approach and a better understanding of the forces at work. On the Centre Block rehabilitation, we were able to demonstrate that the walls could be insulated with marginal or negligible increase in the risks of condensation, mould and freeze-thaw damage, and that factors such as exterior wetting, poor water shedding, structural issues and original detailing of the assemblies would have a much greater impact. This is not a sweeping conclusion that we can apply to all heritage masonry walls. But it does show that by challenging our assumptions and basing decisions on analysis rather than gut instinct, we can come up with better, more sustainable and enduring solutions.
Martin Sing is team lead for sustainability and energy at WSP in Canada, and Chessa Stevens is WSP’s national lead for built heritage in New Zealand. Malene Holmsgaard was director of building preservation at WSP in Denmark until December 2022.