Over-cladding existing homes to improve their energy efficiency as well as aesthetics is proving the solution of choice for local authorities in their bid to meet Decent Homes standards, and more recently, the Community Energy saving Programme (CESP).

At least two councils have used rainscreen cladding panels combined with insulation to refurbish properties ranging from apartment blocks to individual houses, and improved their thermal performance by up to seven times.

Improving a building’s thermal efficiency from the outside is proving an ideal solution for properties without cavity walls and where internal measures would impact on living space – already a premium in many modern homes.

Bristol City Council is currently on the penultimate phase of an eight-year, £15million programme to refurbish more than 2,000 precast reinforced concrete (PRC) houses, including Cornish, Wates and Reema houses, in line with the Decent Homes Act.

All built between the wars to alleviate a chronic housing shortage but now considered defective under the Housing DefectsAct 1985, the generally uninsulated homes are being made more energy efficient, more maintenance-free and more comfortable for the tenants.

The programme started with Airey homes where the original concrete panels were tied into the main concrete support posts of the properties, giving them their rigidity and structural strength. Rainscreen cladding panels from Steni UK were specified for their racking strength which in effect made the concrete posts redundant. More recently, over-cladding the Cornish, Wates and Reema houses with Steni panels has been coupled with mineral wool insulation between the fixing system of a grid of timber battens. This has helped to improve their U-values seven times over, from .0W/m²K to 0.3W/m²K.

The latest solution was designed in-house by the council’s building surveying department in conjunction with main contractor Alfred Bagnall & Sons (West).

Some 70,000²m of Steni Nature panels in a total of four colours – Nordic Spar, Ivory, Pink and Grey – have been fitted by specialist contractor Yewtree Fascias on almost all of the affected units.

The lightweight fibreglass reinforced polymer composite panels feature a surface of crushed natural stone and are resistant to fire (Class O), weather, rot and aggressive environments.

A spokesman for Bristol City Council’s surveying department said: “There are many other products that could be used but some of the locations call for a stronger system so Steni is used. They are the most reasonably priced rainscreen panel and are easily worked and fitted.”

At North Lanarkshire Council in Scotland, work has drawn to a close on a £3.5million refurbishment of two apartment blocks in Motherwell, identified by the Department of Energy and Climate Change (DECC) as an area of low income and therefore a priority for CESP.

Here, some 5,000²m of Steni Nature panels have been fixed by main contractor Lovell Partnerships on the 17-storey Airbles and Whamond towers in a total of five colours – Sienna, Ivory, Sea Green, Salmon Pink and Brick Red. They were specified by the council’s project architect for four primary
reasons. “Their robustness, proven performance, weather resistance and lack ofmaintenance,” said Ian Gillespie. This was to meet the design team’s objectives. “The main priorities were to eliminate water ingress, improve the thermal efficiency of the blocks, and enhance the physical appearance of the external envelope,” he said.

The original prefabricated concrete panel constructions, while structurally sound and considered perfectly adequate when original erected, did not meet today’s thermal requirements.

Part L of the Building Regulations further reduces the thermal conductivity of wall constructions so improving their thermal performance was a major focus of the project for the council.

And since most of the residents were happy in their homes and the cost of demolition and reconstruction was prohibitive, the decision to refurbish – and more specifically over-clad – was not a difficult one.

Works included rainscreen over-cladding to external walls from the first floor upwards, pitched roofs over the existing flat ones, and the replacement of all windows with double-glazed PVCu ones.

“The main element of the refurbishment is undoubtedly the rainscreen over-cladding systems which incorporates the Steni panels. This system incorporates mineral fibre insulation to upgrade the thermal performance of the external walls to current standards,” said Mr Gillespie.

To achieve the thermal efficiency requirements demanded by the specification, the Steni panels were installed on an extruded aluminium sub-frame with was fixed to the original outer skin of the buildings. The cavity created was then filled with mineral wool insulation between 125mmand 200mmin thickness, depending on the level on insulation required.