Chapter 10 - Condensation| NHBC

There are black mould spots above the patio doors and the wall feels cold to touch.

A thermal bridge, sometimes called a cold bridge, is a localised weakness or discontinuity in the thermal envelope (the insulation layer) of a building. Thermal bridges generally occur when the insulation is interrupted by a more conductive material.

As homes become better insulated, thermal bridges become even more significant for heat loss and the likelihood of condensation occurring in specific places increases. These localised ‘cold-spots’ sometimes occur where a critical element has been omitted due to a lack of understanding or communication between the designer and the SAP assessor or the designer and the housebuilder, for instance, a section of loadbearing steel above a large span (such as a patio or double door) where the usual insulated window lintel cannot span far enough.

The thermal bridge can lead to condensation build-up or mould growth, especially in a home where the ventilation systems are not working or the original provision is overridden by occupiers, for instance closing or blocking ventilators. Quite a large amount of moisture is created in homes by normal living activities such as cooking, showering, washing clothes and also by breathing.

New homes are designed to cope with normal levels of moisture generated by occupants, but it is important that the ventilation and heating systems are used correctly and the design and construction have eliminated cold bridges.

Things that can go wrong:

Damp and cold walls;
Mould growth;
Additional heat loss;
Respiratory conditions and poor health for residents.

Future-proofing recommendations:

DESIGN: Design out cold bridges and carefully consider non-standard details;
INSTALL: Avoid product substitutions;
INSTALL: Ensure good communication between designer / SAP Assessor and housebuilder;
COMMISSION: Ensure insulation is carefully positioned in accordance with the design drawings;
MAINTAIN: Ensure the ventilation strategy for the home is well-explained to the homeowner and warn of the consequences of closing or blocking background ventilators or disabling fans.