The importance of breathability and real-world research

The Alliance for Sustainable Building Products (ASBP) says ‘breathability is the most effective way of maintaining stable and harmless moisture levels within the building fabric’.

A healthy building uses natural materials which enables controlled ventilation and vapour- permeability to maintain a balanced environment for both the building fabric and its occupants.

Computer-model based research

The primary issue of previous insulation research which is carried out using computer models is that it isn’t based on real-world performance.

Computers make basic, unrealistic assumptions – such as insulation being perfectly installed, humidity only flowing inside to outside and ignoring leaks – which can wrongly predict the performance of insulation materials.

Six years of real-world data

In 2011, working with the Society for the Protection of Ancient Building and ArchiMetrics, we installed four sensors into the external wall of a two-bed, 1820s home to monitor the real performance of our natural insulation materials.

Unlike a typical insulation upgrade of plasterboard fixed to foam insulation, we installed woodfibre onto a parge coat (Lime Green Duro), followed by a coat of highly-vapour permeable lime plaster (Lime Green Solo) before coating with a mineral paint to retain breathability.

We placed sensors on both the external (S4) and internal (S3) faces of the brickwork, as well as onto the parge coat (S2) and beneath the plaster at the interface of woodfibre (S1). We monitored both saturation and humidity data every five minutes over a six-year period.

Saturation margin (01 Nov 2017 – 30 Jan 2019)

The data, showing the performance of the wall over the most recent period, displays the sensors’ measurements of the saturation margin data.

Condensation starts to occur when temperatures drop below 0°C.

The saturation margin at S1 showed no condensation – as you’d expect with an inside wall where a big drop in temperature would be needed to create condensation.

S2 and S3 also indicated no condensation between the woodfibre and the Duro coat which, crucially, was not the prediction of the computer model.

Moisture was detected at S4 – the external wall – during several periods, particularly during the winter months, suggesting it was affected by wet weather conditions.

Our data disproves the computer’s assumption that temperatures of the external wall and environment match.  Sharp increases in the saturation margin suggesting a hot surface – as a result of direct sunlight – causing vapour to flow back inside of the house.

Relative humidity (01 Nov 2017 – 30 Jan 2019)

S1 experienced stable relative humidity (the maximum amount of moisture the air can hold before saturating) although is influenced by internal humidity: buffering excess moisture before releasing it later. S2 and S3 showed even steadier results, whereas S4 fluctuated with external weather.

Why natural is the only way forward

A breathable building allows vapour to escape and prevents mould growth.  These factors are critical for occupants’ respiratory health and the building’s long-term integrity.

Our research proves that breathable natural products work.  Over the six years, the wall steadily dried out and no condensation was detected.

For more information about the positives of breathability or the products used within our study visit www.lime-green.co.uk or call 01952 728611.