Q: I've been told to watch out for thermal bridges in solid wall insulation. What does that mean?

A: Thermal bridging is often talked about as a major concern for anyone who has an interest in making their property more energy efficient, but what does the term mean? Put simply, it that occurs when you have a relatively small area of your heat loss envelope (the surfaces of your home that are exposed to the cold) that has a much lower insulation value than that which surrounds it.

Heat loss through thermal bridging is usually relatively small - by definition a large area of poorly insulated fabric is no longer a bridge but a normal heat loss element! The main problem with thermal bridging (also known as cold bridging) is that it can cause a focal point for condensation. This can be especially pronounced with well-insulated properties, where any cold spots become can attract a much more pronounced amount of condensation, leading to surface water and mould growth.

Is thermal bridging a problem?

Well, it depends on your specific circumstances. Whether it results in mould is going to depend on a number of factors including the humidity levels, your location (i.e. how cold it is outside), the degree of thermal bridging and your ventilation levels. If you live in a poorly ventilated property and dry your clothes indoors, you may well find yourself with problems. If the Green Deal and ECO lead to a large amount of solid wall insulation being installed, it could be something that becomes a growing phenomenon.

Typically thermal bridges can occur at the following places:

-      window reveals
-      in the corner of a party wall and end external wall
-      where there are solid floor and ceiling slabs
-      poorly un-insulated steel lintels
-      out of sight areas of exposed wall above party walls
-      uninsulated sloping roof sofits

To deal with the problem, the obvious thing is to apply similar insulation to that used elsewhere in the property. However, the nature of the problem often prohibits this – for example where it occurs on a window reveal with limited space.  In this instance the following are other techniques for reducing risks:

1. Apply even a thin amount of insulation if possible.  You may want to use a higher performance but more expensive option for this areas, e.g. aerogel
2. Employ additional, humidity controlled ventilation
3. Reduce moisture vapour i.e. install low flow showerheads, dry laundry in rooms without the thermal bridging

If this is something you don’t fancy tackling yourself, there are plenty of companies out there that can help you. And if you are about to start a refurbishment, it is worth having a think about where thermal bridging might occur and to deal with it before it becomes an issue.

For help with thermal bridging issues, contact info@parityprojects.com. 

About the author: Chris Newman leads on development and delivery of the Parity Projects Home Energy Masterplan.

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