Specialist focus: roofing: Liverpool's Paradise Project

It was always going to be a major challenge to provide the structural waterproofing needed to complete the massive green roof areas specified for The Paradise Project, one of Europe's biggest-ever retail projects. Despite the daunting scale of the task, Hammersmith-based Rock Asphalte has completed more than 90% of its contract, a tribute to the craft skills of its employees.

Liverpool's vast new shopping development, led by main contactor Laing O'Rourke, is one of the most ambitious and eco-friendly in Britain, part of a dramatic phased regeneration scheme in the city costing nearly £1bn. The finished scheme will include one million square feet of shopping spread over six distinct districts, with flagship retail units including John Lewis and Debenhams. Trading will take place on two floors, with cafes covering the paved areas.

However, it is not just retail therapy that will draw people in. The roofs of all the retail units and car parks are being planted with turf, trees and flowers to create a finish that is both beautiful and sustainable. This will be one of the largest green roofing projects in the UK were you to fly over the development, it would look more like a park than a retail complex.

The roofs are not just there to be looked at from afar. Shoppers will walk through these lush areas to get to the next series of retail outlets on a higher elevation. Benches and other features will also encourage them to stop and relax on the green roofing, ensuring they get maximum benefit from their brush with nature. This is as much about creating green public space as about simply protecting the building.

This ambitious design has been possible partly thanks to the use of Rock Asphalte's own fully-bonded Flexiphalte Structural Waterproofing System. This is a combination of Flexiphalte Pommar - an advanced polymer modified mastic asphalt, and Flexiphalte Baryprene - a polymer modified membrane, covering more than 50,000m2.

Asphalting goes green

Rock Asphalte's waterproofing products are mainly being used on the sloping green roofs of the retail units and car parks, protecting the buildings beneath from rain damage or flooding.

To further boost the site's impressive green credentials, any excess rain water will run directly off the surfacing into holding tanks. This will then be pumped back onto the roof when needed, to support the growth and health of the landscaping. This will ensure no water is needlessly wasted, and help the grass and plants remain lush throughout the year.

Many months before construction work began, Rock Asphalte was already working closely with the architect and contractor to develop the design and build waterproofing package. The company had been specified for the £6m-plus waterproofing contract by BDP Architects, with whom it had successfully worked at the Chapelfield Shopping Centre Project in Norwich, where it used its Flexiphalte Triple Protection Inverted Roofing Systems. These systems have also been used over the retail areas at the Paradise Project, and carry a warranty for the designed life of the substrate they are laid upon.

The molten mastic was delivered by lorry in 'hot charge' loads, enabling it to be laid immediately it arrived on site, saving the time and effort of mixing on site.

Designed to be laid 'dead flat' and offering either two or three waterproofing layers, the system consists of a high performance polymer modified Flexiphalte Baryprene membrane fully bonded to the substrate in hot bitumen. Rock's Flexiphalte Pommar, a polymer modified mastic asphalt, is then fully bonded to the membrane.

"This is one of the biggest and most challenging projects we have ever undertaken," says Gary Jukes, contracts manager for Rock Asphalte. "The biggest challenge for us was coming up with a system that enabled construction work to proceed on schedule, with no risk of damage to the integrity of the Flexiphalte system we had laid."

This was achieved, at Rock's suggestion, by adding a 30mm layer of Flexiphalte Pompav polymer modified paving grade mastic asphalt on top of the Flexiphalte Structural Waterproofing System. By doing this, construction and delivery vehicles of all sizes were able to traverse the site without damaging the integrity of the structural waterproofing below.

Opening soon

Developer Grosvenor began work on site in April 2006 and The Paradise Project is due to open for business in March 2008, ready for Liverpool becoming next year's European Capital of Culture. Large-scale buildings on either side of the main pedestrian boulevard at the Paradise Project will offer high quality housing and leisure at higher levels.

"The Paradise Project is the most exciting and challenging project we are involved with," says Grosvenor chief executive Mark Preston. "It sets new standards, makes new rules and will create a new and lasting city centre for Liverpool's people and businesses."

Looking back on his team's work on the scheme, Jukes adds: "Everyone involved with this project is thrilled with how the finished areas look. As soon as you see it, it's clear this is not simply just another concrete shopping centre.

"With so much greenery and landscaping around, The Paradise Project feels very natural and inviting. We are delighted that Rock Asphalte was able to help make this eco-friendly vision become a reality."

The Paradise Project is being funded by the Grosvenor Liverpool Fund, a partnership between private investors and Liverpool City Council.

The Paradise Project will be one of Europe's largest retail projects (top) Rock Asphalte used a combination of products to waterproof the structure (bottom left) from the air, the development's green roofs will look like parkland.