Retrofit for the Future: What Did It Cost?

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Results Now Out


In summer 2009, I and others were involved in setting some of the rules for this competition. They included the minimum CO2 reduction targets to aim for and methods to calculate whether a proposed retrofit would meet the target or not.

Well, the results of the work are now out. The costs incurred have been analysed in a report by the Sweett Group PLC for the Technology Strategy Board, the body which funded most of the RFF project [1].


Interesting Reading


It certainly makes ‘interesting’ reading, as one might say. ‘Interesting’ is an ambiguous word which can be used to express either positive or negative emotions. On reading it to analyse the figures for a client, I think that the predominant emotion should be a little downbeat. We should be thinking along these lines: ‘Well, some of this is very satisfactory, but the bulk of the results are not good enough. How can we do better in future?’


The Bottom Line


The average costs for the measures utilised ranged from moderately high to extremely high. Bearing in mind that money matters to people, the sums involved are inconsistent with the vision of every UK building undergoing a ‘Passivhaus retrofit’ between now and about 2050.

There are circumstances in which such extensive work might be worthwhile. One of them could be an oil-heated solid-walled house undergoing very major renovation. But they do not seem likely to arise on every dwelling.

On average, the cost incurred for external solid wall insulation (EWI) with a slab of plastic foam insulation, usually EPS or XPS, was £123 per m2 of wall area. Strikingly, this is almost 50% more than the ‘mature market’ cost of EWI analysed in a report by Ecofys for the European Council for an Energy-Efficient Economy in 2009 [2]. Based on continental European experience, including Germany, Ecofys documented a cost of around £80 per m2 for 50 mm of EWI plus a marginal cost of around £4/m2 per extra 50 mm of thickness.

Does this 50% ‘premium’ over experience in continental Europe reflect limited UK experience and the resulting ‘learning curve’, combined with a temporary excess of demand over the supply of installation skills? I hope so.

The Sweett report also lists the maximum and minimum costs incurred for the measures. Here I am slightly reassured. The lowest cost paid for EWI was a very modest £56 per m2, suggesting that a significant minority of projects may have paid close to ‘mature market’ costs.

But it could have helped to analyse and present this information if Sweett had asked each separate team how long they had worked on energy-efficient buildings and listed the costs incurred by experienced, average and novice teams. Maybe all the experienced teams did manage to install EWI for £80/m2 or less.


The Future?


Even if EWI can be fitted for £56 to 80 per m2, and other measures for correspondingly ‘reasonable’ amounts, the inescapable logic is that Passivhaus-level thermal retrofits are not set to be universal on UK buildings by 2050. We need to plan harder for how our buildings might meet demanding CO2 reduction targets despite this limitation on retrofit insulation measures.





[1] Retrofit for the Future: Analysis of Cost Data. Prepared for the Technology Strategy Board, Swindon by the Sweett Group PLC (June 2014).

[2] Andreas H. Hermelink, How Deep to Go: How To Find The Cost-Optimal Level For Building Renovation. PBENDE084668. Prepared by Ecofys GmbH, Köln, Germany for European Council for an Energy-Efficient Economy (August 2009).