Product / system manufacture
South East England
Minett Group (aircrete installing subcontractor)
Jumbo Bloks, Celfix mortar, Vertical Elements
Miller Homes decided to take real customers, as well as its supply chain, on a journey towards Code level 6 on the 3.65 acre site. The company has built five identical Miller Zero houses to different levels of the Code for Sustainable Homes. These homes, which are the same in layout to others on the site of 79 units, have been completed to Code levels 1, 3, 4, 5 and zero-carbon 6.
The CfSH houses are among 79 homes for sale on this development. Miller had planning permission for these houses based on 2006 Building Regulations; but as an R & D project, it was decided to construct some of these homes to various levels of the Code for Sustainable Homes. They wanted to know what the development costs would be between each of the Levels and additionally, how much consumers would be prepared to pay for homes created to the Code for Sustainable Homes.
Building as cheaply as possible was not a consideration for Miller; it was about achieving the different Code Levels using different types of materials and construction methods. They also realised it would be the first time that any house builder would test this decision on the open market.
Having tested how the additional construction costs compare, Miller Homes is now researching the public appeal of homes built to different levels. Once sold, each of the homes will be monitored by Miller (with the approval of the owners) to collect data on their lifestyles. The model can then be value-engineered towards possible future sites nationwide.
Although thin-joint is a well established method of construction within the UK, Miller did not traditionally use thin-joint on their housing developments. To align with their determination to create something outside their usual development and build methods, using Jumbo Bloks with Celfix mortar seemed a natural development. Using larger sized aircrete blocks and laying them with a fast-setting mortar enabled the houses to be built in less time. Traditionally, this would also mean a cost saving to the project in time and materials.
The Code level 6 home is super-insulated with the external walls built using H+H’s 200mm Vertical Elements. The Elements themselves have excellent thermal insulation properties of 0.11 W/mK with a compressive strength of 3.0 N/mm2. The Vertical Elements in combination with 200mm WeberTherm insulation and render achieved a U-value as low as 0.09 W/m2K.
Excellent levels of airtightness were also achieved to help meet the mandatory heat loss parameter required for Code 6 Homes of 0.8 W/m2K. This is aided by the fact that the Vertical Elements’ larger panel surface areas of aircrete mean fewer joints, higher levels of air-tightness and of course, improved speed of build.
The Vertical Elements are lifted into place using a “cast in” lifting eye at the head of each 2.4m-high Element, which enabled the contractor Minett Group to build the house in only one and a half weeks. The Elements were installed very specifically by using a layout drawing prepared and supplied by H+H UK, which clearly identified where each element should be placed. H+H also supplied drawn details and information specifically concerning significantly reduced linear thermal bridging, which are possible through the use of H+H aircrete material.
H+H aircrete can achieve significant results on larger developments. A 20-unit development of three-bed semi-detached houses built to CfSH Level 3 using aircrete panels can be used to achieve an external wall U-Value of 0.25W/m2K at a cost saving of £59/m2 compared to timber-framed or SIPS.
The discussions between Miller Homes and H+H on the benefits of using Celcon Blocks and Vertical Elements, along with the support given during the whole R & D project, made a strong case for the use of H+H aircrete for this very unique development.
Miller Homes’ MD for the Midlands and South-East, Ian Beal, was also very keen to challenge the industry’s typical belief that timber-frame is the only material which can reach the higher levels of CfSH.
“For whatever the reasons that timber- frame is so widely associated with sustainability, we wanted to open up the possibilities. No one thought they could build Code level 6 in a masonry design.”
Ian Beal, Managing Director, Miller Homes (Midlands & South)
“The co-operation was already within our own supply chain to make things work in this new territory. This was important, because we wanted a plug-and-play solution to the Code.”
Adrian Corser, Production Director, Miller Homes (Midlands & South)