Are our (highly insulated) walls performing as they should?

ISO 9869-1:2014 describes the heat flow meter method for the measurement of the thermal transmission properties of plane building components, primarily consisting of opaque layers perpendicular to the heat flow and having no significant lateral heat flow.

The properties which can be measured are:

• the thermal resistance,?R, and thermal conductance,?C, from surface to surface;
• the total thermal resistance,?RT, and transmittance from environment to environment,?U, if the environmental temperatures of both environments are well defined.

Thermal conductivity is the ability of a material to conduct heat. High conductivity materials conduct heat well. It is measured in watts per meter Kelvin. Thermal conductance, for instance, is a measure of the ability of a material to transfer heat per unit time, given a unit area of the material or construction build-up and a temperature gradient through the thickness of the material. It is measured in watts per meter per degree Kelvin. that the thermal conductance is the time rate of steady state heat flow through a unit area of a material or construction build-up induced by a unit temperature difference between the body surfaces, in W/m?K.

The following image shows the in-situ real time U-value reading of an existing (poorly insulated) masonry wall.

The heat flow meter measurement method is also suitable for components consisting of quasi homogeneous layers perpendicular to the heat flow, provided that the dimensions of any inhomogeneity in close proximity to the heat flow meter is much smaller than its lateral dimensions and are not thermal bridges which can be detected by infrared thermography.

ISO 9869-1:2014 describes the apparatus to be used, the calibration procedure for the apparatus, the installation and the measurement procedures, the analysis of the data, including the correction of systematic errors and the reporting format.

Zero Energy + Passivhaus have been analysing existing and new built thermal envelope since 2015 when we acquired the U-Value kit from the Swiss company greenteg AG and the gOMS I in 2018. We have now invested in a new improved model, the gOMS II with capacity to analysis up to five points and three building fabrics.

With this addition we increase our capacity to investigate, analysis and optimally dimension the required insulation thickness, specially for existing buildings or to determine the quality of construction for new built.

gOMS also can help to understand existing thermal envelopes without the need to bore holes and accurately estimate the thermal performance quality of masonry in old buildings. We can also examine critical walls, like basements or walls in humid spaces for the risk of mold growth.

In the last decade, we have been using the U-value kit and the gOMS I mainly in listed buildings, where interior insulation is usually used, and leads to high costs and an unnecessarily high reduction of living space, which could have been otherwise avoided with more precise dimensioning.

One of key findings is that, in few occasions, the readings showed that wall structures are not always homogeneous. Therefore, the different walls should be compared with each other using thermographic images. Then, it can be determined which walls should have their U-values measured for renovation planning.

With the gOMS, we can produce an ISO 9869 report wiressly and in a very cost-effective manner. Do you want to know the thermal transmitance of your walls? Please contact us to enquire for more information at [email protected]

If you want to more practical info, you can find here a report from John Gilbert Architects who were commissioned to prepare evidence based, bestcase retrofit design guidance to Renfrewshire Council for their existing housing stock. Report.