Mind the Gap

NBT Updates

As the winter sets in and we all turn up the thermostat, we’re reminded of how inefficient and draughty a traditionally-built home can be. And yet, not much has changed in the way much of our domestic buildings are constructed, perpetuating the problem of poor building comfort and unnecessary carbon emissions.

The problem is that insulation – whether part of a new build installation or used as a retrofit solution – is often considered to be just a tick box exercise, with the designed thermal performance and actual thermal performance often being woefully different. In fact, it’s estimated that a high percentage of new builds fail to meet their designed energy performance target. Considerably worse than that of a certain car manufacturer.

Part of the problem is that the thermal performance of the building is assumed to be directly correlated to the thermal conductivity of the insulating material, but this assumption does not take into account any gaps or other materials that can be incorporated between and around sections of insulation.  Even a tiny opening of just 1mm can have a significant impact on the thermal performance of the building envelope, so the thermal values of the insulation should be considered as part of a complete solution that includes airtightness.

Insulation works best when it is used as an external thermal wrap for the building, creating seamless continuous protection against the ingress of cold air from outside and the loss of heat from the inside. It’s important to be mindful, however, that outdoor temperatures are not cold all year round, so improved year-round comfort can be achieved by using woodfibre insulation, like Pavatex, which provides excellent heat buffering to ensure an ambient indoor temperature during the summer months.

To aid thermal performance wind tightness, many of the woodfibre insulation boards within the Pavatex range – including Isolair, Isoroof, Pavatherm Plus and Pavatherm Combi – are designed with tongue and groove edges to provide a neat and snug fit that protects the join between sections of insulation to encapsulate the building envelope.

For improved airtightness, the Pavatex range also includes breathable airtightness membranes, some of which incude self-adhesive strips, which are used to provide both a vapour control layer and an airtight barrier for the building envelope. These are installed in combination with our airtightness tapes to seal any joins in the membrane, in much the same way that the taped seams on your windproof jacket ensure that cold air cannot penetrate and warm air does not escape.

The whole system must be designed into the building alongside a suitable ventilation strategy. Reluctance to specify airtightness into buildings still persists because of the misconception that stale air will be trapped in the building, but, with good design and a holistic approach to designing healthier buildings, this is not the case.

It is surprising just how much energy is lost through the loss of warm air that leaves a building when it’s cold outside. Perhaps building more airtightness into their projects is a resolution that all architects, developers and contractors could make for the New Year.