Energy and CO2
The Code for Sustainable Homes presents considerable challenges, particularly with regards to thermal performance, enhanced insulation and reduced air leakage. To answer these challenges, The Concrete Centre has published a new guide that demonstrates how to achieve the Code’s mandatory energy and CO2 requirements with masonry and concrete
Of the nine of design categories in the Code, Energy and CO2 accounts for up to 36 of the available 100 points. This reflects the importance placed on minimising operational CO2 emissions relative to the other included environmental impacts.
The new guide, ‘Energy and CO2: Achieving targets with concrete and masonry’, is based on research carried out by a working group comprising members of the Home Builders Federation (HBF) and the Modern Masonry Alliance (MMA). The research found that the standard of fabric performance required at each level of the Code can be achieved with the systems and materials already available. However, ongoing improvements in the performance and cost of renewable technologies and products such as triple glazing will assist future code compliance, particularly at high levels.
Key conclusions from the guide include:
The Code Challenge
At each level of the Code the challenges for different house types are the same for all materials
No single approach
No single design approach to minimising CO2 emissions will suit all house types. For example, houses with a large exposed area will benefit most from improved U-values, whilst smaller attached units will benefit more from the introduction of renewable energy.
Wall U-values – code levels 3 and 4
A U-value of between 0.2 and 0.28W/m2k for external walls was found to be appropriate for code levels 3 and 4.
Wall U-values – code levels 5 and 6
At code levels 5 and 6, the optimal U-value for all types of wall construction may probably be around 0.15-0.17W.m2K, reflecting the best balance between overall CO2 reduction and insulation costs.
Orientation
Orientation and passive solar design have an important role to play in optimising heating energy requirements and the performance of active solar systems. The thermal mass of concrete and masonry construction allows full benefit to be made of passive solar design.
Air leakage
Concrete and masonry can provide robust, long-term solutions to airtight construction and can achieve air leakage rates below 2m3/(h.m2) with good site practice and detailing
Airtightness at code levels 5 and 6
At code levels 5 and 6, insulation and airtightness requirements are essentially the same for all construction systems, and the emphasis shifts to the provision of renewable energy.
Cavity width
A cavity width of 150mm can provide a U-value of 0.15W/m2K, which equates with Passiv Haus performance and is suitable for the highest level of the Code.
Of the new guide, Guy Thompson, head of architecture at The Concrete Centre said: “It is clear that there is no single solution that can be used for all dwelling types. Those that have greater exposed areas, such as detached houses, will benefit more from improved U-values. Terraced and flats will benefit more from the introduction of renewable energy. For most dwelling types, level 3 can be achieved without renewables and in all cases level 4 can be reached with the addition of limited renewables. This guide focuses on the issues in the context of masonry and concrete construction and provides the answers”.