Home Features Projects Harper Square adopts a new Drytech façade system

A new façade system has been adopted on a housing development in south London for the Family Mosaic housing association. London-based Drytech Façades has used an energy efficient and space saving concept to achieve high performance standards in the façade. Adrian JG Marsh reports.

Technical performance is all important for social landlords as part of their drive to achieve the targets set by the Code for Sustainable Homes and tackle fuel poverty for tenants who are less able to compete in the open market.

Family Mosaic’sHarper Squarescheme is a seven-storey development in the Elephant and Castle area of Southwark,London. A series of five individual buildings linked with shared stairwells will include 75 apartments. Walls in the new complex demand exceptional U-value of 0.15W/m2K so that it meets the thermal performance proposed as standard for new-build in the 2016 Building Regulations.

In October 2011 Drytech Façades was appointed to carry out a £1.4 million 3,200 m2 façades package which included coloured glazed terracotta rainscreen and Marley Eternit pre-finished cladding board. Drytech also took on responsibility for installing windows.

“The architect was looking for a very low U-value which traditionally we would have achieved with a standard metal framing and then built up the insulation on the outside of the studs,” said Richard Horobin, operations director at Drytech Façades.

In conventional systems, the insulation is applied externally and so adds to the thickness of the walls, decreasing the amount of lettable or usable space. Horobin’s team proposed using the new Knauf ThermaFrame solution which places the insulation in the frame itself so that it is sandwiched between the gypsum-based sheathing board and the internal plasterboard, solving the problem of usable space.

Drytech Façades worked with Knauf Façades to put forward alternative designs to the original SFS design because an alternative solution using structural insulated panels had already been considered and rejected because of its higher overall build cost.

The first indicative specification employed 195mm Knauf ThermaFrame stud, with a 95mm internal Z bar together with Knauf ThermaFrame insulation, Knauf Windliner and two layers of Knauf ThermaFrame Liner VC taped and jointed internally (split between the internal Z bar).

Once the main contractors, Lovell Partnerships, had approved the indicative design, Drytech and Knauf worked with the project architect and engineers over eight weeks to produce detailed drawings for the five blocks.

Works were planned to maximise productivity and ensure that critical deadlines were met. The façade design also reduced on-site activity as metal sections were prepared off-site and delivered in a predetermined sequence.

Richard Horrobin said: “We’ve found that the Knauf ThermaFrame meets the U-value required without the need for any additional external insulation, which can sometimes interfere with the support work required for the finishes or cause condensation.

“The system can also accommodate wind loadings of more than 1.0kN/m2 and would carry the deadload of the terracotta rainscreen. The new system also has 90 minute fire resistance that would otherwise mean we would have had to install dense products such as mineral wool insulation or cement particle board.”

Drytech has handed over the façades package and the whole scheme is due to be completed this year. Its sister company secured the drywall installation package.