Solarcrest offer breathable open-cell and vapour protection closed-cell spray foam insulation suitable for walls, floors and roofs
What to look out for
PIR between rafter on a 5M premiership home
100mm of gappy PIR between
the rafters of a £5M luxury home
The latest interlocking cavity insulation installed by an engineer
Interlocking PIR cavity wall insulation installed by bricklayer
Energy Performance Gap
The Difference Between Design & Reality

Imagine you bought a new car that was supposed to do 30MPG, but the first time you filled it up you discovered it only achieved 20MPG at best. This car is not an occasional commuter, you're going to be running it 24x7, potentially forever. Not doing what it's designed to do is bad for your wallet not to mention the environment. Now substitute 'car' for 'home' and assume that gap in performance is going to happen if you don't intervene during the construction project.

In terms of buildings, a performance gap with the insulation is very common. The Centre for the Built Environment at Leeds Beckett University claim the average gap between predicted and measured performance is 60%, That's 60% more fuel burnt and 60% more emissions than intended. Many are over 100%. But that's not the full story. A performance gap often exists with the heat recovery you put in to ventilate your 'eco' home too. The Building Research Establishment claim this is over 100%. Pretty sad when you consider most new houses are built with a performance gap because developers can 'get away with it'. Don't rely on building control to spot the errors, it's not their department.

The links below explain why the performance gap occurs and what Solarcrest can do about it. It's not so much the materials that are used, but the way they're installed. Gappy insulation lets heat out and gaps are almost impossible to avoid. When warm air escapes and meets a cold surface condensation risks increase too. Adding an airtight membrane might make it airtight, but half a millimetre of material doesn't stop much heat escaping. What you ideally need is airtightness through the whole roof or wall assembly, without stopping the passage of vapour.

For ventilation the performance gap is caused by convoluted ducting, which adds unnecessary air resistance, which then overloads the motors. The ducting gets convoluted because the installer is given the cheapest materials to work with instead of the best.

Here's some more reading if you want to mind the gap.


If you're building or renovating Solarcrest can prevent a performance gap. It starts with the right ventilation because that goes in first. Without it you can't have the airtightness that makes your insulation work.

spray foam insulation applied below the roofGet a proposal now
spray foam insulation applied below the roofSend plans to sales@solarcrest.co.uk
call us for a spray foam insulation quoteCall 01625 423020 for help