Miller cracks the Code for Sustainable Homes

Miller Homes is conducting an unusual experiment in Basingstoke. It is constructing six houses to each of the six levels of the Code for Sustainable Homes, to work out how much it costs to build them - and what consumers are prepared to pay. By Will Mann.

"You don't have to build revolutionary houses to achieve Level 6 of the Code for Sustainable Homes. That's what we set out to prove with this project and that's what we've done."

Ian Beal, managing director of Miller Homes (South), is talking about a small housing scheme dubbed 'Miller Zero' in Basingstoke. At first glance, there's appears little remarkable about the row of six identical houses. But therein lies the beauty of Miller's experiment.

"We had received planning permission from Hampshire County Council for these houses based on the 2006 Building Regulations," explains Beal. "But then we thought, why don't we try to build each of the six houses to each of the six different levels of the Code, as an R&D project, to establish how much it will cost us every time we move up a level, and how much the consumer will be prepared to pay?"

In that respect, this is the first attempt by any house builder to test a Code 6 home on the private market.

The first house on the street, already sold, has been built to 'base level', ie. the Building Regulations, rather than Level 1. (Miller decided to leave out Level 3, feeling that building to the other five levels was sufficient for its R&D purposes.)

Move along the street, and up through the code levels, and while the houses look the same, a few features are subtly different. So, for example, the upstairs airing cupboard is the same in each house, but the size of the mechanical plant inside increases further up the levels.

Smart metering

All houses have a mechanical ventilation and heat recovery (MVHR) system, plus smart metering, and all bar Level 1 have water saving baths, WCs and taps. Rainwater harvesting features on Levels 5 and 6, with a 2000-litre tank used for non-potable services.

At Level 3, the first renewable feature is introduced - an air source heat pump. Because the project is driven by R&D, Miller has chosen to trial different renewables at different levels. Level 4 features a ground source heat pump, Levels 5 and 6 biomass boilers and photovoltaic (PV) panels.

Similarly, different insulation methods have been used. Levels 3, 4 and 6 have aircrete panels supplied by H+H Celcon, Level 5 uses Kingspan TEK Structural Insulated Panels (SIPs).

"This exercise wasn't about building to each level as cheaply as possible - more to find out what we could achieve and what we could learn from different types of construction," says Beal.

"Obviously some features are only suitable in certain circumstances. For the ground source heat pump, where we drilled a 90m-deep bore hole into the chalk layer below, we had to do extensive testing to ensure the geology was right."

Costliest feature

The costliest renewable feature Miller has used is, by quite a distance, the photovoltaics. On the Level 5 house, 14m² has been installed, with 40m² on the Level 6 house - at a cost of roughly £1,000 a square metre.

Certainly, building green is not cheap. The 'base level' house, constructed to the Building Regulations (2006), cost £98,000 to build, and has been sold for just under £300,000.

Progress up the levels of the Code, and the building costs mount, though the sale prices don't necessarily rise by the same percentages. Beal reckons Level 3 cost an extra £5,000 to £7,000 on top of the base level, most of that coming from the air source heat pump, with a further rise at Level 4, due to the £8,000 ground source heat pump.

Level 5 cost an extra £30,000 on top of the base level, the steep increase down to the PV, while Level 6 adds on a whopping £50,000.

And here's the rub: valuations Miller has received for the Level 6 home price it at £340,000. That would mean the cost of building to the top code, compared to the base level, translates into a £10,000 loss per unit for the house builder - maybe more if it doesn't get the asking price.

"It's a big issue," says Beal. "The problem is the renewables. If the requirements for these were less stringent, the costs become more manageable. The government needs to look at it because house builders aren't going to start building homes at a loss."

Of course, there is a saving on running costs via cheaper utility bills. At the bottom end of the Code, this is fairly minimal at around 10%, but the ground source heat pump cuts a typical household's energy bills by about two-thirds, and zero-carbon Level 6, of course, is completely energy self-sufficient.

Will that tempt consumers? Once the units are sold, Miller will run a monitoring programme with the residents for a year. "This will tell us what consumers really want from these homes, and how they behave," says Beal. "Because that's what we really need to know.

"Will they see a Level 6 home as having extra kudos, or will the higher purchase price put them off, even with the saving on utility bills?"

---

Using masonry to build to the Code

Despite a perception that timber frame is necessary to hit the higher levels of the Code for Sustainable Homes, Miller has proved otherwise.

"We believe strongly in a masonry envelope, we don't believe in timber frame, and we wanted to prove that a masonry system could work up to Level 6 of the Code," says Ian Beal.

To achieve this, Miller Homes turned to aircrete panel supplier H+H Celcon. On the homes built to Code Levels 3, 4 and 6, the house builder used full-storey 200mm thick Vertical Elements aircrete panels supplied by H+H, applied with 3mm thin joint instead conventional mortar.

On the zero-carbon Level 6 house, where a tighter U-value of 0.09W/m²K had to be achieved, the aircrete panels were used in conjunction with internal dry lining, plus a 200mm rendered external insulation, supplied by WeberTherm, which also offers a 'water-shedding' finish.

This caused minor complications with installing external features such as the front door canopies, which had to be fastened through the render on to the aircrete panels.

H+H claims that on a larger, 20-unit development of three-bed semi-detached houses, built to Level 3, aircrete panels can be used to achieve the required U-values of 0.25W/m2K at a cost saving of £59/m² compared to timber frame or SIPs.

---

So what has Miller learnt from the exercise?

"One thing we've learnt is that our subcontractor base is up to the job," says Beal. "Our M&E contractors Turnpike and AH Electrical had no problems with the renewables installations. LB Plastics came up with a bespoke, triple-glazed window design for Levels 5 and 6, where the air gaps between the glazing are filled with Krypton rather than air."

All the houses conform to the 'lifetime home' standards, so the downstairs toilet can be adapted to a shower, there is room in the entrance lobby for a wheelchair to turn around, and the stair is wide enough to accommodate a chairlift.

The biomass boiler has to be fed with wood chips costing £2.50-a-bag. "It means more maintenance by the homeowner," admits Beal, "but the way we are marked by the Code, this counts as carbon neutral because the carbon from the wood chips has previously been absorbed so does not count as a fossil fuel."

Beal believes a future project could achieve greater energy efficiencies at reduced construction cost - depending on planning. "This was an R&D project, but if we were building with purely commercial considerations in mind, we would probably have had the biomass boiler serving the whole street," he says. "We wanted to put up a wind turbine, which could also have served several homes, but the local authority would not agree to it, even when we asked for just a temporary one for our own research purposes."