Thermal phase shift is the time delay between the moment of peak outdoor temperature and the moment that peak temperature is reached on the inside of a building element. It is expressed in hours.
A longer phase shift means that the interior temperature will be less affected by outdoor heat, helping to keep indoor spaces cooler for longer. A shorter phase shift means that heat penetrates more quickly into the building, potentially increasing the need for cooling in the evening and early night.
Ideally, the phase shift should be calculated based on the entire build-up of the construction. This provides a realistic picture of the total thermal performance and allows for evaluating the contribution of each layer — such as the insulation — to the overall delay in heat transfer.
Phase shift depends on the type of material, its thickness, and its mass. For example, a flat roof system using 100 mm PIR insulation (such as IKO enertherm) on top of a 160 mm concrete structural deck results in a phase shift of 8.2 hours.
For tailored advice and performance evaluations, contact your IKO advisor.