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How green is a good retrofit?

Grosvenor 119 ebury street inarch ltd
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The kind of detailed, three-dimensional thinking architects excel at needs to be applied at scale if we are ever to get out of the climate mess we are in, says Hattie Hartman

This is World Green Building Week, the seventh in a series of annual events spearheaded by the World Green Building Council, the global network of organisations working to influence local building industries in the direction of sustainability. Almost a year on from the Paris climate change agreement, at which nearly 200 nations committed to limits on emissions to relatively safe levels, it is an apt moment to reflect on where we are in the UK.

With more stringent regulations in effect in the UK, new buildings are increasingly designed to perform better. And there is progress in the retrofit sector, too, as the range of projects showcased in the AJ Retrofit Awards (AJ 15.09.16) earlier this month demonstrates.

Sustainable retrofit is nowhere more difficult to accomplish than in listed buildings

As ever, residential retrofit remains the biggest challenge, representing over half of UK built environment carbon emissions, according to the Green Construction Board’s Low Carbon Routemap (2013). With 2012’s Green Deal acknowledged as a resounding failure and now scrapped, we must look elsewhere to see what’s next.

Sustainable retrofit is nowhere more difficult to accomplish than in listed buildings. Of the UK’s approximately 500,000 listed buildings, over 90 per cent are Grade II-listed, designated by Historic England as ‘of special interest’.

Two recent retrofits of Grade II-listed residential properties – one targeting Passivhaus EnerPHit (‘Quality-Approved Energy Retrofit with Passive House Components’) and another BREEAM Outstanding – have painstakingly explored the limits of what can be achieved. Both projects highlight a key question – how green is green enough?

Prewett Bizley’s upgrade of an 1820s Grade II-listed building in Bloomsbury targeting Passivhaus EnerPHit (AJ 15.09.16) has transformed a former solicitors’ offices into a daylight-filled home with greatly increased comfort. Three types of moisture-open insulation – wood fibre, aerogel and spray-applied foam – were meticulously applied to the internal face of the terraced property’s external walls.

16js 10 detailsection

16js 10 detailsection

The heating load was slashed by 90 per cent, with secondary glazing (a measure which required 18 months of negotiation with Westminster Council) delivering about a third of the savings. Overall carbon emissions reduction is predicted to be just under 80 per cent. Concealing ducts and pipes and two MVHR units in service voids, the architect led the services design, which was completely worked out at feasibility stage. Prewett Bizley’s signature axonometric drawings show the service runs down to the duct and pipe dimensions.

Also in Westminster, David Morley Architects’ comprehensive overhaul of a run-down hotel at 119 Ebury Street into three high-end rental properties for Grosvenor reveals the same thorough-going approach. For the majority of its listed properties in Westminster (which comprise about a quarter of its Westminster holdings), Grosvenor has targeted a 50 percent reduction by 2050. At Ebury Street, Grosvenor opted for an ambitious 80 per cent savings by 2020 and achieved BREEAM Outstanding at design stage.

Grosvenor 119 ebury street rear extension inarch ltd

Grosvenor 119 ebury street rear extension inarch ltd

Source: Grosvenor

119 Ebury Street, refurbished by David Morley Architects

Modelling heat loss of the existing building revealed that 27 per cent was through external walls, and a further 24 per cent due to air leakage. Just as in the Bloomsbury property, the challenges were insulation and secondary glazing. Airtightness, measured at the outset at 17ACH at 50Pa, was to be reduced to 3. The original windows were refurbished and secondary glazing installed. Rooftop PV panels are predicted to meet about 10 per cent of the properties’ electrical load. The entire building will be monitored, along with a property a few doors down on the same terrace retrofitted to Grosvenor’s standard specification to provide a baseline.

It’s all well and good for a major London landlord to showcase an exemplar and for a private client with a generous budget to test the limits of sustainability, but what can be intelligently replicated more widely, and how? And what role can architects play?

The recent refurbishment of a former Victorian hunting lodge, Bicester Town Council’s Garth House – shortlisted for the RIBA President’s Awards for Research – suggests another way forward. Undertaken by Oxford Brookes University together with Bioregional, pre-refurbishment monitoring of both building and occupants informed a refurbishment strategy (a rapid-fire proprietary internal insulation system cut off-site, secondary glazing, and improvements to heating and ventilation), which was deployed while occupants remained in situ and achieved a 58 per cent saving in energy consumption.

These are impressive outcomes, though greater architectural involvement would have resulted in more sensitive installation of secondary glazing.

The obsessive holistic, yet detailed, three-dimensional thinking reflected in these projects is what architects are so good at. If we are ever to get out of the climate mess we are in, this thinking needs to be applied at scale – and not just at the top end of the market.

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