Barbican, London

We were asked to replace the covering on the distinctive barrel vault roof that caps Frobisher Crescent, a semi-circular block next to the Barbican Arts Centre. We were called in after the recently installed liquid-applied roof material had failed and started leaking. It’s part of an ongoing development by United House to re-convert the building back to flats – for most of its life it was used as a business school.

The building’s grade II listing is extensive so there was pressure to maintain visual aspect in terms of colour and preserving the smooth barrel lines, while complying with Building Regulations on thermal performance. We won the contract by looking at it holistically and working with the membrane and insulation manufacturers.

We preserved the smooth curve of the vaulting by using Rockwool mineral wool insulation boards, approved by the Single Ply Roofing Association (SPRA), which were pre-cut on the back to follow the tight radius of the successive vaults. The boards are covered by a single ply membrane from Sarnafil. It’s a green product and it complies with Part L on thermal performance.

We were able to get the membrane in traffic white to match the listing requirements. The membrane can also be cold applied, reducing the fire risks associated with alternatives such as bitumen felt, which is applied using hot wax.

The roof is only four floors above the hall in which the London Symphony Orchestra plays, and even drilling into the roof with a 5.5mm drill can be heard throughout the building.

So we installed a galvanised steel subframe to reduce sound transference while drilling.

Brendan McNulty, managing director, Delomac Roofing