Diminishing returns
We insulate to prevent heat loss, so the more the merrier, right? Not necessarily.
Both Building Regulations and the Passive House standard dictate certain minimum u-values (or heat transfer through a surface) for elements forming the external fabric. Insulating is likened to putting a puffer jacket on your building and zipping it up tight. So why not two puffer jackets?
Firstly, someone’s paying for that second jacket and how do you prove it’s actually needed? Too much insulation becomes unhelpful and cumbersome – just try tying your shoelaces wearing two puffer jackets. There is a Goldilocks Zone where you have just the right amount. PHPP can be used to run scenarios for different insulation types and thickness. This shows that adding more insulation delivers diminishing returns in performance past a certain point. Designers can use this throughout the design to test and tweak the insulation within each element to find the optimal thickness.
No Insulation without Ventilation
In retrofit projects there’s also a mantra ‘no insulation without ventilation’, which seeks to prevent the unintended consequences of adding insulation without considering the wider impact on the rest of the fabric. Insulating will raise internal temperatures and lead to a greater air tightness, which is a bad combination if the ventilation is already poor. Insulating can lead to fundamental changes in the way a building manages moisture and in the worst cases, lead to internal condensation, interstitial condensation, and mould growth.
Insulating is the best way to reduce space heating demand and bring down the carbon footprint of our buildings, but use it wisely. Seek guidance from an experienced Retrofit Coordinator and Retrofit Designer on how to apply the right materials in the right places and to ensure there’s enough insulation to be both useful and economic.
