What’s working - Offsite technology

Lemon Tree House, London, Affinity Sutton Group

Project

In common with many urban locations, the 0.14ha site for 49 homes and two floors of retail space faced severe access and storage restrictions. The project was on a “red route” that prohibits parking at any time and it was impossible to get the usual articulated lorry on to the site. In addition, the building was to be on top of a London Underground Tube line so had to use the existing foundations. Contractor Avebury also agreed to work closely with an adjacent special needs school to minimise disruption and to provide education opportunities to the pupils during the project.

Avebury designed and built the project along with structural engineer John Allcock. Mechanical and electrical services were provided by Brentwood.

The Brief

Affinity Sutton selected Avebury to deliver the project as it planned to use its timber frame Wave technology – a joint venture with Riverside Housing Group. This would allow for offsite manufactured products to be delivered on a “just-in-time” basis, minimising the need to store materials on site. It also meant that the lighter materials would not require the foundation strengthening to protect the Tube line that are needed for heavier traditional approaches. Avebury also promised that the project would be delivered in 15 months, with the main construction period taking half as long as traditional construction methods. At one stage, Avebury claimed it was building a floor every week.

Feedback

In its November 2005 report into modern methods of construction, the National Audit Office found that the key factor preventing new technologies such as timber-frame housing from delivering cost as well as time savings over brick and block techniques was a lack of upfront planning.

In common with the other two schemes covered in this section, Avebury had to rework the original designs as they were not done with the specific MMC in mind. That said, Wave director Stuart Gee says his team was allowed a six month lead-in time in which to address issues such as where and how to get the electrical services through the floors; what panel sizes would need to be used; and how long each phase of lifting the panels into place would take. “We spent six months on the planning phase,” says Gee. “This was very generous as we usually only get eight to 12 weeks. It also helped that we had a complete set of plans as opposed to the usual argy-bargy you get on other projects.”

He points out that this detailed planning meant that the savings in the amount of waste generated both in the production phase and on site “really were incredible”. A recent report into the project by Avebury found that, when compared with traditional construction methods, there had been 30% less waste in production and 60% less waste on site with 90% recycled in total.

Besides the lengthy planning phase, Gee credits this to the supply chain: “It is critical to us as we have no factory ourselves. We use Pattrick & Thompsons, which is part of Walker Timber Group, and Finnforest. They are absolutely key to us in terms of the engineered timber product they provide.”

Another way that Avebury was able to cut down on the amount of time taken and waste generated was by ensuring that 70% of the materials required to complete each floor were lifted into place by crane before the next floor was installed. “We didn’t have to go back and cart materials around after we’d finished each floor,” says Gee. “It was mainly materials for the internal lining: sheet material like insulation for the floating floors and plasterboard.”

What is worth repeating?

As a result of the success of the project, Avebury commissioned cost consultant Davis Langdon to evaluate the scheme in comparison with traditional construction. It found that the cost – at £1,400/m2 – was to the lower end of what would be expected for more mainstream methods. Gee is confident that this can be improved and aims to boost the 300-400 homes that Wave builds each year to 1,000.

One point worth making

‘We had an active fire alarm system on every floor. Also there is no smoking allowed on site – you just don’t do it’
Stuart Gee, Wave

Products used

brick cladding: Wonderwall, Hanson Rhenophol
roofing: Oakleaf Roofing
carpets: Home Call Carpets
landscaping: Land Structure
metal work: Arlec
lifts: Schindler
windows: Col Secure
rainscreen cladding: Terreal Rainscreen, fitted by Astley
brises-soleil: Levolux fitted by Astley

Houndmills, Basingstoke, Sentinel Housing Association

Project

The proposal for this site on the edge of the town centre in Basingstoke had been proving tricky to get through planning for Sentinel Housing Association. It had submitted designs by HTA Architects but the council wanted more shared-ownership housing and Sentinel was unable to structure a deal that stacked up financially.

The breakthrough in what became a 162-home scheme came when Sentinel approached developer Fleming to form a joint venture. The Irish company was keen, having only recently launched in the UK, and the two formed Vestal Developments. Fleming decided it would use its own Fusion Structural System, which is a series of modular pods built in its factory in Cork. However, this presented some difficulties as the HTA plans had been designed for traditional brick-and-block construction. Fleming commissioned architect PRP – with which it had worked on English Partnerships’ Summit House in 2005 – to rework the designs. Also on the project team were structural engineer Barrat Mahoney Engineers and M&E contractor Rybka.

The Brief

The aim was to halve the project construction time and gain an EcoHomes rating of “very good” from BRE. One hundred of the homes would be for rent and shared ownership with the remainder being sold by Fleming. Houndmills was also to be a series of three blocks, the tallest of which would be 12 storeys – the highest building yet built with this pod system, according to Fleming.

Feedback

In all, more than 400 pods were manufactured and shipped from Ireland to Basingstoke, which meant that Fleming had to work closely with its architect and client to ensure that what was being designed was precisely what was needed.

Once Iain Thayne, chief executive of Fleming UK, and his staff were satisfied that their project team was familiar with the constraints of designing a building whose pod components, because of transport restrictions, could not exceed 10.2m by 4.6m, they concentrated on preparing the site. “We did the foundations and then built the core; then we came in and stacked the pods,” he says.

So far so simple. Yet with some of the 400 pods weighing up to 20 tonnes and the process of lifting them into position lasting 12-13 weeks, Thayne says it was anything but. He points to the integration of the M&E elements of the project as being a key lesson, given its height and scale. He also says working at the height that was required to hoist pods onto the top storeys was a “major crane operation”.

Once all of the pods were in place, Fleming added the steel roof before “mixing off and on site … [by] going back to the more traditional techniques of cladding” the exterior of the blocks.

Establishing a factory in the UK would go some way to helping Fleming combat the common accusation levelled at modular pods that all they do is effectively transport air from the factory to the site.

Thayne adds: “The reality of the system is that a load of stuff is going to be transported to a site regardless. Plus, you will only have one lorry turning up at the actual site as opposed to loads under traditional building.”

What is Worth Repeating?

Thayne attributes the popularity of the scheme to the fact that Fusion is run by a “builder turned manufacturer”. Fleming plans to open a UK factory that will be able to produce “at least 2,500 pods a year”. It generally takes two to three pods to make each flat, giving a capacity of about 800 homes a year.

One point worth making

‘Logistics are a big issue for us. The largest thing on the road is 10.2m by 4.6m and has to be escorted’
Iain Thayne, Fleming

Products used

external brickwork and render: Weber System
rainscreen cladding: Glasal
roof: Kalzip
windows: Schüco
lifts: Kone
boilers: Atmos
glass block walling: Luxcrete

West Rainton, Durham, Three Rivers Housing Association

Project

This is the first time that this type of offsite technology has been used on a volume housing scheme in the UK – despite the fact that it has been used extensively throughout the USA and much of the rest of Europe for the past 30 years. Housebuilder CGR Ecohomes decided to use the insulating concrete formwork (ICF) process after searching the internet to try to find an approach that would allow it to develop low-carbon homes. ICF is based on hollow, lightweight blocks made from insulating material that lock together without the need for cement. This then provides a formwork system into which concrete is poured. The eight-home first phase was awarded an innovation prize by best-practice body Constructing Excellence. Working with CGR Ecohomes were structural engineer Portland Engineers and architect Anthony Watson.

The Brief

Three Rivers wanted to build a series of bungalows that would meet the EcoHomes “very good” requirements. To do this, all of the U-values in the homes had to be below 0.19. The client was also keen to see reduced levels of carbon during the construction of the project.

Feedback

CGR Ecohomes was able to meet the requirement to cut carbon emissions during the construction phase without too much trouble – the ICF process uses up to 40% less carbon than traditional brick-and-block construction. An added benefit of the technique was the speed with which it allowed the homes to be built. “We were able to do two semi-detached bungalows in two days,” says Les Baxter, business development director for CGR Ecohomes. “It is very light so no heavy lifting is required. Also, it’s a semi-skilled job so it’s possible to train people to do this wherever you go.”

Baxter adds that the costs of the materials was on a par with what he would have expected if using traditional building techniques. This was helped by manufacturer Beco Wallform striking a bulk purchase deal. There was a similarly negligible impact on costs in the design phase. This was despite the fact that architect Anthony Watson had initially designed the project for brick-and-block construction. “West Rainton had standard foundations and only a few changes were required to the design to use ICF – nothing major. Insulation was now already included in the wall for example,” says Baxter.

He adds that it is a mystery to him why some of the larger housebuilders have not yet begun to use ICF. “Thousands of homes have been built in the US and the rest of Europe using it. The only things that housebuilders need to work out in using this stuff is what the design possibilities are with it, and the structural engineers need to work out what its loadbearing capability is. They are just reluctant to change from the systems they have now as they know how they work and they are easy to cost.”

Although Baxter has nothing but praise for the ICF system, he was less happy with the manufactured roofing system that he bought from a company in Belgium. “It was a sandwich of insulation and hardboard. It was a complete nightmare to be honest and very expensive.

We went by the U-values as this gave us 0.16 and I wanted to get below 0.19 or below. It came all the way from Belgium and then didn’t have any ties with it for lifting. So we had to make our own sling to hoist it into place. I definitely wouldn’t use it again. We are using attic roof trusses on the second phase, which is going up just now.”

What is worth repeating?

CGR Ecohomes was only set up last year and this was its first project, but Baxter says the company will only use ICF from now on. He says it is about to start work on a four-storey project in Chesterfield and that, by the end of the year, the firm will have built 80 homes.

“We are hoping to hit 200 homes this year and within five years to be doing 500 homes a year,” he says. “We have the interest already and are struggling to meet demand. I have lost count of the number of people who have called me up about this scheme and wanted to see it.”

One point worth making

‘It is incredibly strong. We accidentally put a wall in the wrong place and it took us two days to knock it down’
Les Baxter, CGR Ecohomes

Products used

roof panels: Unilin Unipur
roof tiles: Marley Modern
wall structure: Beco Wallform 313 System
windows and external doors: John Watson’s
render: Alsecco
heating boilers: Glow Worm
insulation: Kingspan
kitchens: Symphony