A new lease of life; retrofitting and upgrading two 1960s blocks behind the iconic Regent’s Crescent

Iain McLellan sets out how these two buildings were saved.

Two existing buildings with 92 apartments have been retrofitted and upgraded, while the residents remained in occupation. Designed and built in the 1960s, they form part of the new Regent’s Crescent development which reinstates residential use to the Grade I listed crescent.

Located at the rear, these buildings were part of a facsimile rebuild following bomb damage in WW2 when the crescent was developed as a series of offices. The recent decision to take down the ‘60s office development and rebuild did not include these two blocks, instead, a strategy was formed to save and upgrade them using a fabric first approach.

The two buildings join with the rear of Regent’s Crescent, they remained occupied throughout the construction phase

The transformation of these two buildings is truly remarkable, demonstrating how a failing building can be saved and given a new lease of life for many decades to come. A key challenge for this site was how to assimilate the new envelope with its 1960s proportions and levels to connect aesthetically with the new rear façade of the heritage building, with its Regency proportions and levels.

Of typical design and construction of the time, the two poor quality, concrete and masonry buildings were fitted with a large proportion of single glazed Crittall windows; apartments were cold in the winter and tended to overheat during the summer months. In addition, the masonry was spalling, to the point where it was cracking and falling off the building, so a potential danger to the public.

The existing buildings joined to the rear of the office development rebuild of the 1960s, the arched windows to the facsimile facade are just visible through the office windows

A total retrofit overclad solution was conceived with a thermal upgrade to the envelope comprising the roof, windows and walls. An external fabric first approach was needed so the residents could remain in occupation. The works were all very carefully organised with new windows fitted in a day per unit before the external cladding was installed. There were occasions when some tenants moved out for a short time.

At eight storeys (22 metres) high, the design team needed to make very careful product decisions, in particular with regard to Building Regulation 7, in terms of the classification of the insulation used and it's combustibility. Products in line with the more rigorous standards were selected.

The warm jacket consists of a mineral wool, rendered wall insulation, selected for its high energy saving performance with aluminum faced timber windows to provide acoustic attenuation from the site conditions and traffic. In terms of ratio from an existing masonry wall, a 100mm overclad insulation is a major improvement. However, the thermal mass of the existing walls was recognised to assist with reducing the diurnal temperature changes and release of energy into and out of the building. Thermal bridging was checked at all key floor and window junctions, and fire and cavity barriers were installed. Smaller measures such as increased overhangs to windows also assist with the cut off from summer radiation.

The roof improvements involved installing tapered insulation to work to existing rainwater outlet positions without affecting parapet levels. Additional works included the replacement of the outdated boiler which provided centralized heating and, for aesthetic reasons, the replacement of communal doors and upgrading of corridors.

The increased thermal performance has led to significantly reduced energy bills for residents. The improvements have almost halved the space heating demand in each unit (there were no works to the internal heating infrastructure). More importantly is perhaps the significant improvement to comfort levels with overheating considerably reduced and acoustics improved.

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