Thermal Bridging In Passive Houses

If insulation is the heart of the passive house then thermal bridging is one of the two banes of the building process.

In passive house design the envelope must have no thermal bridging.

In many ways the detailing of junctions to eliminate thermal bridge is the secret of passive house design.

All buildings have junctions.

These are where the floor meets a wall or where a window in installed in a wall or where the roof and walls meet.

So how can a house be build without thermal bridging?

The answer is careful design allied with thermal modelling

This analysis gives the heat transfer effects of thermal bridging.

So what exactly is a thermal bridge?

A thermal bridge or cold bridge as it is sometimes called is created when materials which are poor insulators come into contact.

They occur at building junctions and when determining the heat loss a one dimensional calculation is not adequate so two dimensional or three dimensional calculations is usually required to determine heat flow.

Thermal bridges are either

• Repeating Thermal Bridging such as wall ties

• Non Repeating Thermal Bridging such as window cills or window lintels

• Geometrical Thermal Bridging at say a wall corner junction

The funny thing about thermal bridging is that it increases as the amount of insulation is used on elements such as walls and roofs.

As you insulate an element such as a wall or a floor the thermal bridge will intensify the heat transfer.

Thermal bridging is the major contributor of condensation.