Homing in on zero-carbon

Maybe it is the nation’s preoccupation with self-build TV programmes but the terms ‘concept’ or ‘eco homes’ have become bywords for properties equipped with the latest green ’bling’ and expensive grand-designs. While there is a place for pushing technological boundaries and showcasing cutting-edge architecture, the reality is that they do not show how the UK can deliver volume, low cost, energy efficient and ultimately zero-carbon homes.

Current economic factors aside, we face major challenges. The reality is that the Government’s zero carbon targets for new homes remains in place. There is also a critical need to understand how to build to Level 6 of the Code for Sustainable Homes (CfSH) on budget and at the same time tackling housing shortage by delivering 240,000 new homes by 2016.

The Tarmac Homes project, which is part of the University of Nottingham’s Creative Energy Homes initiative, will see the construction of two concept homes which will aim to create a blueprint for volume, zero carbon housing.

Two semi-detached homes (one property will be built to Code Level 4 and the other to Level 6) are being built using tried and tested masonry products and techniques by Tarmac and its partners, Lovell, the University of Nottingham’s School of the Built Environment and project architects Bill Dunster architects.

It is generally accepted that the first step to meeting the higher levels of the CfSH is to improve both the fabric insulation and the air tightness of the structure. We plan to include 100mm of partial fill insulation in the brick and block cavity walls of the Code 4 house and will be using a biomass boiler to provide space heating in combination with solar hot water for both homes.

Meeting Code Level 6 is a tougher challenge and the use of onsite renewable technologies is necessary. For this property, the external walls are being constructed from a single leaf of Tarmac aircrete blocks with external insulation and render finish. Along with the solar hot water system we have included photovoltaic panels (PV) on the roof to accommodate the electrical demand from lighting, pumps and fans and all the domestic appliance load.

How will our decision to build using masonry products affect our ability to reach the highest levels of the CfSH? We are confident that masonry products are able to meet this challenge and, in doing so, we will help to address some of the industry misunderstanding of the BRE’s Green Guide 2008 ratings.

It is important to remember that building low and zero-carbon properties is about delivering an overall sustainable package which is not just governed by one material or technology. The environmental impact of materials is assessed by the Green Guide 2008. It looks at a range of materials or products used in a number of building structures (such as walls, floors and roofs) and assesses their overall impact over a 60 year study period by measuring against 13 impacts such as climate change, mineral resource extraction and fossil fuel depletion. The Green Guide then awards each material a score in ‘Ecopoints’ and takes the overall impact of the best and the worst results for a particular structural element and building type. It divides the gap between them into six equal bands, E (highest impact) to A+ (lowest impact).

There is a worrying misconception across the construction industry that only A+ materials detailed in the Green Guide can be used to build at the highest levels of the CfSH. This is simply not true and the reality is that a building is the sum of all parts and using one criterion such as embodied carbon or recycled content to make specification choices will not deliver an efficient building. It is worth noting that many existing masonry construction elements meet A to A+ Green Guide Ratings.

One of the key issues that needs to be understood is the importance of considering whole-life energy performance of building products and techniques – not just the embodied energy. Examining the way materials and products perform ‘in-situ’ is key to delivering energy efficient and zero-carbon homes, and is, in fact, an issue that has been highlighted by BRE.

Responsible sourcing is another key element of the CfSH and throughout the build we are looking to ensure that 80 per cent of materials are responsibly sourced. Within the CfSH, up to 6 credits are awarded for achieving a level of responsibly sourced elements such as ground floors, roof, external walls, internal walls and staircase. Up to 3 credits are awarded for responsibly sourced finishing elements such as stair, windows and fascias.

While the use of recycled materials is not one of the direct measures detailed in the Green Guide, many of the materials used within the project contain a proportion of recycled materials such as Tarmac Hemelite (lightweight aggregate) blocks where the average recycled content is 47 per cent.

How is the Tarmac Homes project tackling site waste management?

Lovell, our project partner is operating a site waste plan which includes procedures to reduce site waste in accordance with best practice. In addition, we have a clear commitment to sort and divert waste from landfill.

Block waste from site will also be removed and recycled as part of Tarmac’s Take Back Scheme, an initiative with HIPPOWASTE™, the national waste solution provider which has been already rolled out to Tarmac customers.

The Take Back Scheme involves disposing of all off-cut blocks in special bags. Once 10 or more bags are full, HIPPOWASTE™ collects and transfer them to a Tarmac recycling facility or manufacturing site. The recycled aggregates produced by crushing and screening of the blocks will then be re-used within the block production plants or supplied to other Tarmac recycling customers.

The Tarmac Homes initiative is a live testbed for the construction industry to understand how it is practically possible to use existing masonry products and techniques to build at the highest levels of the CfSH. Despite the current economic downturn, the Government’s 2016 target still remains and it is vital that we use this project to understand how to deliver affordable and scaleable zero-carbon housing now.