Let’s reveal the importance of reveals

Barry Turner’s picture shows how IWI is commonly fitted

There will be some research coming out soon that starts to explore the importance on the detailing aspect of insulation works.

The work has focused on the issues of thermal bridges around windows and doors. These thermal bridges (cold spots) that are created by the fact that many insulation systems do not insulate around doors and windows (the reveals). The norm for most insulation works is to stick on lots of insulation to the main walls, but the more complicated and difficult reveals are just left devoid of any insulation.

The effects of missing this insulation vary between properties because houses have different types of wall, different sized windows and doors, different orientations, … However, it is possible to model the thermal performance of the house to see what effects are likely. Bearing in mind that ‘all models are wrong, but some are useful’ one cannot predict exactly how any one situation will play out in real life but there are some useful pointers that come out of the work.

One of the worked examples shows that by applying 100mm of insulation to the walls only is actually less energy efficient that applying 20mm of insulation to all the surfaces (i.e. including the reveals).

The trouble is that you generally need a thin insulation around windows so that the operation of the windows and doors are not impeded. The main insulation companies use cheap EPS insulation systems and these boards are too thick for use around reveals. So they don’t. If you wanted to use a thin insulation material like aerogel then this would be deemed to be incompatible with the main system and hence would invalidate any warranty offered. So people are left with having the choice between a warrantied insulation system that won’t work as well as predicted and might actually cause some ‘unintended consequences’ (resultant cold spots can attract condensation and mould) and a system that would probably be much more efficient, but would not be guaranteed. Unfortunately we tend to err on the side of caution when we have such major refurbishments undertaken. Of course only time will tell if the warranties that companies offer are actually worth their salt. One imagines that they will be toothless and won’t be worth the paper that they are written on, but we shall see.

The issues of reveal insulation are applicable both for IWI and EWI (Internal and External Wall Insulation), but the timescales, knowledge and budgets associated with the most of this work will mean that an opportunity for better improvements will be lost. What makes it worse is that already companies are having to go back to the work that they did a couple of years ago and un-do much of it. This is a shocking waste of money, resources, carbon as well as a double dose of disruption for the householder. 

Work for groups like the Passive House Trust and others seems to be highlighting that actually doing thermal improvements properly would save more carbon than the mass roll-outs are actually producing. There is a cost issue associated with this as each property would be more expensive to insulate (due to more expensive materials being used and the time required for the detailing). The idea of doing fewer buildings properly is not as attractive to politicians as mass roll outs to the fuel poor, even if the carbon savings would be greater.

The trouble with the decision making system in the UK is that it is driven by the tools that are available to it. The use of things like Energy Performance Certificates and the spreadsheet assumptions that underpin it mean that reveal detailing is not taken into account. Moisture and condensation risks are also not part of the calculations. So the extrapolated predictions that are created by EPCs are fundamentally wrong and misleading, but it is all that councils, Government and Housing Associations have to go on. So no wonder we continue to store up problems in our housing stock. I feel a hobby horse coming along!!


The importance of reducing thermal bridging is really important in terms of energy efficiency and carbon reduction, so if you have any control over the process at all we would recommend ensuring that insulation in the reveals is specified and installed correctly. Easier said than done, but getting insulation right is possible, it’s just that you need to be aware of the ‘pinch points’.