No, not a recipe for a quiet night in, but rather the ingredients of Adnams’ deep green distribution centre. Thomas Lane went to Suffolk to meet a brewer with a difference

From the road near Southwold in Suffolk, the distribution warehouse of Adnams’ brewery is barely noticeable. The building sits in a hollow, so the gentle, rounded profile of its enormous green roof blends in perfectly with the surrounding fields. Its architect, Aukett Fitzroy Robinson, is perfectly at ease with this discreet presentation because its building is noteworthy for its environmental rather than its visual credentials – in fact, it is billed as Britain’s greenest warehouse.

That said, its handsome appearance belies its utilitarian function, and the green roof softens its 4,500m2 footprint. The roof, in turn, is supported by enormous curved glulam beams, which are described as the largest ever installed in the UK. Instead of the standard crinkly tin walls usual for this type of building, the exterior is finished in white render, and sits on a brick plinth. This hides one of the building’s most radical features – cavity blockwork walls made from lime and hemp, with the gap between the two skins filled with yet more lime and hemp to give the walls a U-value of 0.18W/m2K.

With the additional insulation provided by the roof, the building does not need a mechanical plant to keep the beer inside it cool, even in the summer, which means lower carbon emissions. Now the building is finished, the team can relax in a virtuous green glow. But pioneering the UK’s first commercial use of lime hemp construction was challenging. How did they get on?

For client Adnams, environmental responsibility is a part of its core values. Andy Wood, its managing director, says it was important to put this into practice at a reasonable expense – the £5.8m building cost 15-20% more than a conventional shed. “If we want to set an example to our customers and shareholders we have to put our money where our mouth is,” he says. “But it’s also a good business decision. This asset will have a life of at least 30 years, which will more than compensate for the costs, and second, the decision was based on a long-term view of energy prices. We estimate the energy savings are between £50,000 and £60,000 a year.”

Aukett Fitzroy Robinson presented Adnams with a menu of options, including rainwater harvesting, solar panels and green roofs. “We had to justify how much extra each option was costing and the payback periods. Plus, it had to meet Adnams’ criteria for operational efficiency,” says project architect Nitesh Magdani. Straw bales were considered for the walls, he says, but discarded because of worries over fire, vermin and strength.

A company called Lime Technology advised on the practicalities of using lime render over straw, but ended up suggesting an alternative material – lime hemp. “Lime hemp had some way to go for this application, but it had the advantage of having been used in France for the past 20 years,” says Ian Pritchett, managing director of Lime Technology. Helped by research funding from Adnams, Lime Technology worked with structural engineer Faber Maunsell and the University of Bath to develop and test a block solution – previously the material had been cast in situ like concrete. “Part of the reason for the blocks was so that contractors knew they could use a normal construction process – we didn’t want to put them off,” says Magdani.

Clearly this strategy worked since

Haymills, the firm that took it on, saw it as a fairly conventional job, with a fast-track 40-week programme. “When we looked at it, we didn’t realise the complexity,” says David Lott, Haymills’ contracts manager. “It wasn’t until we moved onto site that we realised how complex it actually was.” The first challenge was the glulam beams, specified because they contain less embodied energy than steel. The 40m long beams are the longest ever used in the UK.

The size of the beams worried Lott. Getting them delivered from Denmark was hard enough, but then he had to find a way to put them up. “We had numerous meetings on the methodology,” he says. The problem was keeping the steel columns and beams in place while they were fixed together.

Luckily, Lott heard about Mick King, a timber structure expert who runs a firm called Woodworks. “He suggested the crane sizes and the methodology and even made some models to show how the beams would swing round,” explains Lott. “It was amazing – we thought we would need scaffolding, but he said it wasn’t necessary.”

The solution was to use a crane to lift the beams. Straps were tied to each end, and these were attached to weights that anchored the beams in position while they were connected to steel columns.

With the structure up, Haymills started on the lime hemp blockwork. The timescale of the programme meant that 60 bricklayers were recruited to lay the 90,000 blocks. “The blocks were a challenge,” says Lott. “The first lot crumbled – they were terrible. They got better as the job progressed, but they needed careful handling to prevent the corners being knocked off.” Another problem was that the blocks were heavy and the bricklayers found them exhausting to use.

Five courses of blocks were laid, then left for four days for the lime mortar to go off before the lime hemp infill was placed. This was to prevent the pressure of the infill collapsing the newly laid blocks.

This stage also tested the patience of Haymills. “The idea was to pump the lime hemp infill in, but there are only two or three suitable pumps in the world. We tried to modify a hedge-trimmer, but in the end we had to shovel it in by hand,” says Lott. All this extra handling meant Haymills had to bring in extra fork-lifts to lighten the load.

If Haymills thought they were on the home stretch once the blockwork walls were up, they were wrong. The lime rendering had to be added by conservation specialist IJP Building Conservation, a sister company to Lime Technology. The tight programme caught them out, and Haymills had to bring in a local firm of plasterers and trained them up.

All these factors added 10 weeks to the project. And Haymills was hit by the unexpected costs of the additional plant needed to handle the materials. “We haven’t lost any money, but we haven’t made the margin we should have,” says Lott. Despite this, all the parties involved in the project, including Haymills, are keen to do another one. “It was so rewarding. The feedback we got was incredible,” says Lott. “It’s not just be another warehouse in Suffolk.”

Don’t smoke it – build with it

So what’s so special about hemp? Hemp is cannabis sativa – the same as species as the proscribed drug, but without the psychoactive THC. It does make an excellent green construction material, however. Once treated, it won’t degrade, it is fireproof and it is unattractive to vermin.

When mixed with lime, it can be used to construct walls. It has several advantages as a material: it is an excellent insulator, and it allows walls to “breathe”, so moisture inside a building can pass to the outside. It is also green because it takes just 14 weeks for one hectare to produce enough hemp to build a house. It is also carbon negative, in that it locks 80 tonnes of carbon in its walls; if it had been built out of conventional brick and block, it would have produced 450 tonnes.

According to Lime Technology’s Ian Pritchett, one reason for turning the lime hemp into blocks was so that the team could use the same codes of practice as they would for conventional blockwork diaphragm cavity walls, which made the approvals process easier. But Pritchett says the Adnams experience has taught him that the future isn’t in blocks. “There is now sufficient knowledge and confidence in the material that means we don’t have to go down the blockwork route again. We would do it in situ,” he says. “It’s faster and more economical.”

Lime Technology has just built itself an office using “Hemcrete”, the name now given to the material.

Pritchett says the company will be supplying Hemcrete for an education building at the Centre for Alternative Technology in Wales and 26 social housing units in Elmswell, Suffolk. A single side of shuttering is erected and Hemcrete is sprayed on to this to the required thickness, then smoothed off, ready for rendering.

It was also seen as a conventional construction process that would appeal to builders.