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What is thermal bridging in insulation, and should I worry about it?

Posted by Chris Newman on 22 January 2013 at 2:10 pm

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 

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

If you have a question about anything in the above blog, please ask it in the comments section below.

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5 comments - read them below or add one


derekcfoleyComment left on: 24 September 2013 at 5:17 pm

Hi Nick, Very interested in your posting, I've often thought about going back to the old ways and have a larder.

I'd say your issue is most likely due to condensation forming at the warmest point on the insulation, this often happens in highly insulated loft spaces, where the condensation can damage/rot timbers.

I'd suggest two solutions to this:

1) you could try adding more ventilation, to help dry out the condensation


2) Increase the thickness of the insulation on the wall inside the house between it and the larder, this will cause the natural "dew point" to be deeper within the insulation, and if it is something like kingspan or celotex, then this can be eliminated completely if it is thick enough. I'd consider adding a second layer over the top of the same thickness. This should solve the issue, unless you have warmth leaking into the space in some other way, e.g. through the floor, which again, you might also insulate to the same amount - don't forget to do the same on the door too.

I'd do the second option as 1) is caused by 2)

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Parity Projects

Parity ProjectsComment left on: 24 January 2013 at 9:29 am

Thanks Prescient Power

Its definitley a big worry for some installations.  An illustrated example:

A solid wall house undertakes some internal insulation under ECO. Around 75% of the walls are insulated but the hardest or most expensive are not.  Also costs are kept down by just doing flat surfaces and reveals and sloping soffits are ignored.  Additional, appropriate ventialtion is not provided and the windows remain single glazed but have some draughtproofing carried out.  All this is probably 'acceptable' under Green Deal / ECO, and the economics would drive this to be a prefered solution.

There will be a high likelihood of damp and mould growth where there previously was none.

The reliance on installer training is a bit of a red herring as we are not aware of any requirements to undertake formal training on a holistic approach to responsible retrofit.

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Parity Projects

Parity ProjectsComment left on: 24 January 2013 at 9:21 am


I'll have to speculate a fair amount here...the damp is most likely coming from warmer air from inside the house coolling down in the larder and so its relative humidity is increasing and so water is condensing out.  Only a few things that could help:

1) draughtseal the door so that air only gets in when you open the door

2) increase the ventilation and if the two airbricks are not top and bottom to facililtate circulation then add ventilation at the top and bottom.

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Prescient Power Ltd

Prescient Power LtdComment left on: 23 January 2013 at 3:14 pm

A really clear, informative blog Chris. Thank you!

It will be interesting to see how many installers of the Green Deal recognise this problem and deal with it accordingly.

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Nick Hanna

Nick HannaComment left on: 22 January 2013 at 5:12 pm

Interesting..I guess this may explain a problem I have had: we built  a larder cupboard about 18 months ago with about 5cm of insulation on the 2 walls inside the house and two airbricks to the outside. It's very cold and works perfectly as a larder but I have noticed damp on the top of the wall inside of the cupboard recently and couldn't understand why as I couldn;t see anything wrong I guess this is somewhere with 'deliberate' cold bridging, but I;m not sure how to deal with the damp problem?

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