Towards Zero Carbon (26-Sep-07)
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Full story: Towards Zero Carbon (26-Sep-07)
The Government has specified that by 2016 all new houses should be zero carbon rated. In June 2007 The Stewart Milne Group, one of the UK’s leading privately owned house builders, celebrated the completion of its first five star rated, near zero carbon show homes. The homes have a range of environmentally friendly features, and are designed to meet all nine elements of the Governments Code for Sustainable Homes, it is expected that they will go into commercial production well in advance of the 2016 target.
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With the news that by 2016 all new houses should be carbon zero rated, Director of Product Development Ross Peedle talks through Stewart Milne Group’s innovative Sigma project.
Written by James Hurley & Produced by Nicholas Davies
One of the UK's leading privately owned house-builders, Stewart Milne Group has enjoyed consistent growth since it was established in the North East of Scotland in 1975.
The Group is split into four Operating Divisions; homes, timber systems, construction, and developments.
As the company expands and looks to position itself as a UK-wide operation – it recently unveiled a new UK-wide commercial property division – it is looking for innovative ways to meet the range of legislative, environmental and commercial challenges that house-builders are facing.
Sigma project
By 2016, the Government has specified that all new houses should be zero-carbon rated, and there will be stamp duty exemptions given for homes meeting the criteria. In June, Stewart Milne Group celebrated the completion of its first five-star rated, near-zero carbon showcase homes – pre-empting the guidelines by almost a decade.
At the Building Research Establishment (BRE) innovation park in Hertfordshire, the company created two versions of its Sigma homes to demonstrate a number of new configurations and innovative technologies.
“We’re quite a diverse organisation,” says the company’s Director of Product Development Ross Peedle. “Sigma means ‘the sum of all things’, and in this project we’ve pulled together all of our combined knowledge of the market place to take things as far as we could.”
The two houses it completed have a range of environmentally friendly features, heating water from solar panels and using electricity that is generated from roof turbines and photovoltaic tiles.
While the houses could be viewed as a well publicised experiment, the applications and implications of the designs behind them are genuine and far reaching. The homes were designed to meet all nine elements of the Government's Code for Sustainable Homes and are expected to lead to commercial production well in advance of the Government's 2016 target.
“With the Sigma project, we were trying to do two things. Firstly, we were trying to respond to the sustainable development agenda, with increased energy efficiency and the use of mixed renewable energy technology which gave us the five star code rating. We were also looking at the end user and trying to pre-empt what they might be looking for ten years down the line.
“The houses are unusual in their layouts for a volume house builder. They’re very open plan and contemporary. We were trying to gauge whether the market has moved on from the traditional three storey, boxy town houses that you see up and down the country towards something that’s more design led,” Peedle explains.
While Sigma house at BRE was a prototype, the company is looking to learn a number of lessons from the project. “We’re looking for customer feedback to measure and monitor the performance of the building. For example, do the turbines do what the manufacturer said that they’d do? We’re going to produce a next generation of the Sigma home and expand it into a Sigma village.”
In May, Gordon Brown announced plans to build 200,000 eco homes on brownfield sites to create what he called ‘eco towns’. The then Chancellor said that more sustainable and affordable homes would have to built to soothe the UK’s housing shortage.
Brown said that he envisaged "communities with combined heat and power with a whole range of eco measures including better public transport, cycle lanes that actually make it possible for us to have a very much higher quality of life in our new buildings and in our new towns".
Stewart Milne Group believes that its sigma homes will be a perfect fit for these ‘eco towns’. “We hope to work with the public sector agencies and the housing corporation to identify suitable development opportunities to take this into a larger context and away from the prototype status it has at the moment,” says Peedle.
The company currently has an internal steering group devising a strategy for this. “Within a year we’re hoping to have secured the opportunity to be working on a live site. We want to have identified where the sigma village opportunity is going to be, who we will be working with and all the land issues that come with this sort of project.”
Lessons learned
With the Sigma project, Stewart Milne group has proven that there is a lot that can be done with the energy efficiency of the building during the construction process, but it also arguably highlighted some gaps in the current thinking on the future of renewable developments.
“Sigma goes along way to meeting some of the sustainable development criteria which are being raised. Where we have a bit more of a conundrum is on integrating micro renewables within our buildings, and we’re really not sure about that as a strategy for the future,” says Ross Peedle.
“It’s incredibly expensive to do, and we have some real doubts as to the performance of solar panels and wind turbines in particular. We know that there are also all kinds of legislative and insurance obstacles. The NHBC (National House-Building Council) won’t insure any of these products which are fixed to buildings.
" Adding all of this up, we just don’t see it as a viable option.” Peedle says that a sensible solution would be for house-builders to focus solely on the fabric of the building to maximise efficiency. “It’s quite encouraging to see government starting to think along those lines as well.”
The Home Builders Federation and British Property Federation have recently backed the proposal to scrap the so-called "Merton rule", which requires builders to obtain at least ten percent of a building's energy from sustainable sources such as solar or wind power.
“Most developers would be delighted if the Merton rule was scrapped. We don’t think it’s commercially viable or that the technologies are there to deliver that yet. Generating green energy is a great idea, but not at the micro renewable scale in tight urban locations. Some of the major energy providers are probably better placed to provide that than house builders,” he says.
Supply chain
To make advancements in the construction process, the company set itself some highly challenging targets, not all of which could be met at the prototype stage. “We had been relying quite heavily on air tightness in the buildings. We had a very ambitious target of achieving an air tightness factor of one when a more normal factor would be around ten. We found that incredibly hard to achieve.
We had a team of guys for four days sealing and taping all the joints and even with all of that, and some very careful attention to detail at the design stage, we found it incredibly difficult to achieve those targets.
“Another part of the code rating is water consumption targets which are fairly onerous for a five star house. The figure that we’ve achieved at the sigma house is eighty litres per person per day, where a more typical figure would be 160 litres per person per day,” Peedle says. “Bath and shower water is used to flush the toilets and rainwater is collected and stored for watering the garden.”
However, the firm did run into a familiar problem that afflicts companies working in innovative areas. “There aren’t enough products around which are able to achieve these kinds of figures. The supply chain is going to have to move some way before we have enough choice in the type of dishwashers, washing machines or taps that builders will require, so there’s a lot of work needed.”
Much of the project’s success can be attributed to a combination of the versatility of timber frame construction and the advantages of off-site construction. Stewart Milne is the market leader in the UK in timber frame, with approximately 25 percent market share. “We are familiar with what is happening in Scandinavia and the States where timber frame is very poplar. With Sigma, we introduced a new acoustic floor, which was originally pioneered in Scandinavia.”
The DB50 floor cassette adds increased sales value and reduces the total cost to customers by removing nine processes that clients formerly needed to perform on site. It uses normal timber joists with slots cut in them which act as a dampener. “It’s an excellent advancement as it gives robust detail of acoustic separation. It does away with the need for a floating floor system which is normally the case with a timber separating floor, so it speeds up the process on site. It also reduces costs and is quicker and easier to install.
The Sigma house employs a steel frame bathroom pod, which is integrated into the design, sitting on timber floor cassettes. “We wanted to show that it is possible to integrate pod and hybrid technologies with timber frame as well as more traditional forms of construction. This sped up the finishes on site because the bathrooms were effectively pre-finished. We also used a cassette roof so we could control the manufacturing in a factory. At the upper levels, this allows bedrooms with vaulted ceilings which can add value for the end user.”
Timber frame wall cassettes are craned into position, so the timber frame panels come to site fully sealed and with a services zone built onto the inside. “Once the electrical services are fitted just a final plaster boarding is required. The advantage of that is the main thermal zone isn’t broken into,” explains Peedle.
Peedle praises the advantages off-site construction brings, and anticipates this becoming an increasingly significant for house-builders.
“Quality control is much easier to secure in the factory environment. Factories work to quality standards way beyond what most sites are capable of working to. That’s certainly an advantage and the speed of erect is a major factor for us.”
As house-builders construct multi-storey flats where nothing can be sold until the whole building is completed, or suburban house buildings where it’s difficult to achieve maximum value until the whole environment is completed, anything that boosts speed of construction will bring a significant advantage. “Doing more in the factory - we see that as the future.”
- Source: Construction Digital
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