Types of thermal bridge

There are three types of thermal bridges:

1. Point (3D)

2. Linear (2D), and 

3. Area/Field (1D)

   
   

👉 Point Thermal Bridges

These occur where discreet shapes pass through the thermal envelope, for example steel beams, columns, and roof anchor points.

Impact on thermal efficiency 

On their own, the relative impact of point thermal bridges on the efficiency of an envelope can be relatively minor. However, as envelope performance improves generally, the relative impact can be material particularly if there are lots of repeating elements across an envelope.

Also structures with specific thermal requirements, like coolstores or labs, are other applications where point thermal bridges may warrant mitigation.

Addressing potential condensation risk

Where they definitely do warrant careful consideration is where condensation is a risk, either due to climate conditions or project specific factors such as indoor swimming pools. In these cases, mitigating the effect of point thermal bridges may be a worthwhile investment (and essential in some cases).

Linear Thermal Bridges

These are thermal bridges that run along or up a thermal envelope such as slab edges, floor/wall connections or balcony connections. 

🔎 Magnified impact on thermal efficiency 

Their impact on a building envelope’s thermal efficiency is often significant because of the long ‘effective edge’ of the thermal bridge. This is magnified even further for elements like balconies that are repeated across a building envelope. That’s why investing in mitigation measures such a slab edge insulation has very good bang for buck in terms of lifting overall thermal performance (and why it’s a code requirement in many climate zones in NZ).

A famous (in building science at least 😉) example where the impact of linear thermal bridges is bemoaned is the Aqua Tower in Chicago - coined a ‘thermodynamic obscenity’ by building science guru Joseph Lstiburek. 

Average/Clear Field Thermal bridges

These are really a combination of point and linear thermal bridges, grouping them together to make it efficient to estimate the impact of thermal bridges over a larger area such as a wall or a roof. For example a timber stud wall with fasteners and insulation would be ascribed an average thermal bridge value (thermal transmittance).