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Egg-shaped primary school uses offsite construction to get ahead of the curve

The design process for Birmingham’s Four Dwellings Primary School gave it an unusual elliptical shape. Offsite construction and prefabrication of the timber frame and roof panels ensured a speedy programme and minimal costs.

Four Dwellings Primary School in Quinton, Birmingham, does not look like an ordinary school: it’s egg-shaped. The 1,600 sq m new-build school shares a campus with its sister high school and was constructed under Birmingham’s Building Schools for the Future programme in 2012.

Main contractor Lend Lease used offsite construction and prefabricated components on the project, speeding up the build and enhancing the project’s sustainability credentials.

Shape born of the design

The building’s unusual elliptical shape came out of design meetings between the architect dRMM and the school’s senior management and pupils, as project architect Adam Cossey explains.

“We were given a pretty well-defined brief about what the school needed to do,” he says. “We allowed management to arrange the classrooms as they wanted, and a circular shape leading from nursery around to year six soon emerged.

“The main hall would be in the middle, with group learning areas placed in the corridors so that they were not just used as dead circulation space. This became a very simple egg-like shape.”

Timber chosen for the frame

After examining a number of options, the team decided to use a timber frame for the building, with prefabricated components made by Framewise in its Welsh factory.

“Cross-laminated timber is now used quite widely in the UK, particularly on education projects, and we considered it here before choosing timber frame construction,” Mr Cossey says.

“As well as being quick and cost-effective, the timber frame also allows for future adaptation much more easily than steel or concrete”

Adam Cossey, dRMM

The timber cassettes were made offsite, with panels consisting of an oriented strand board on one side that could be insulated if required, and a breathable membrane on the other.

“It allowed for an incredibly quick construction process,” Mr Cossey explains. “The panels were brought to site and it was a case of literally screwing them into place on the sole plates.”

Prefabricated timber was not just chosen for its programme benefits, however.

“As well as being quick and cost-effective, it also allows for future adaptation much more easily than steel or concrete,” Mr Cossey says. “And it’s far more sustainable.”

Prefab roof saves time and boosts sustainability

The other major prefabricated element of the build was the roof. Prelasti EPDM sheets were used – 1.2 mm single-ply membranes originally developed by Pirelli from the by-products of making tyres.

AAC Waterproofing supplied the material for the project, which was chosen for a number of reasons.

“The membrane is very sustainable and the prefabrication process reduced the amount of time spent on site in a similar way to the timber frame,” Mr Cossey says. The 1.2 mm thickness also meant the material was light enough for a timber-bearing structure.

Following the receipt of CAD drawings and a site survey, AAC bonded the Prelasti EPDM sheets together in its factory to create panels up to 500 sq m in size.

“Creating a curved school out of straight elements was the biggest technical challenge on the project”

Adam Cossey, dRMM

The bonding technology is known as vulcanisation, and it involves heating the material to 200 deg C to join the sheets at molecular level, ensuring there are no seams.

On site, the bonded membrane sections were rolled into place, trimmed to fit and adhered to 150 mm flat board insulation and a vapour control sheet.

“We again looked at a number of different roofing systems but settled on Prelasti for these reasons,” Mr Cossey explains. “The components were able to just be glued and screwed onsite, providing a very quick construction process.”

Creating the curve

A datum line was used with individual sheets bonded in stepped lengths to recreate the curve required for the building’s elliptical shape.

“Creating a curved school out of straight elements was the biggest technical challenge on the project,” Mr Cossey says. “It took some head-scratching to find a solution to this on the timber frame, and we came up with a hanging element that could help to generate the curve.”

“The solution was an aluminium ‘helping hand bracket’. This was fixed back to the timber cassette panels and the distance the bracket protruded could be adjusted, allowing for vertical and horizontal timber battens to be fixed, generating the required curvature.”

The western Cedar timber shingles, interspersed with polished stainless steel shingles, were then fixed backed to the timber battens allowing for the curved facade to be formed.

With both the timber frame and the roofing elements of the build using prefabricated components made offsite, the school opened in time for the new term in September last year. The children moved straight in to the new building as planned.

“The components allowed a simple and cost-effective build that fit in with our design and the levels of sustainability we wanted,” Mr Cossey says.

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