Low energy is a key issue in building specification and must be considered alongside sustainability criteria. Barbour Index and Scott Brownrigg offer some suggestions
1. Take a balanced view
Energy use has been a topic of concern for decades, but with the onset of global warming it has recently taken a leap up the political agenda. This has fed through into tougher Building Regulations, making energy use one of the specifier’s key considerations. Balancing low energy use during construction with other sustainability issues, such as lifetime energy use is critical.
2. Know your materialsSpecifiers should ensure that they understand the criteria being considered. Ensure when you are specifying a material that it meets the client’s requirements, and remember to balance high embodied energy material like concrete against its everyday energy performance and long life. Also carefully consider the building’s use pattern to specify targeted energy conservation measures.
3. Consider thermal performanceThermal performance takes into consideration a number of terms, typically thermal resistance (R-value) or thermal conductivity (K-value). The U-value is an overall measure of thermal transmittance through a section of the building. It takes account of the R-values of all the material used in that section and allows for surface transmittance and any air gap. Remember the U-value is only a relative guide as U-values are based around static conditions that hardly ever apply in the real building. Also, the law of diminishing returns applies to improving U-values after a certain point, so it may be more cost-effective to save energy in other ways such as installing efficient boilers.
4. The airtightness issueConsideration of the building’s air infiltration rate is another key issue that is being brought into focus by Building Regulations. Infiltration now has to be checked in most buildings by pressure testing. Specifiers need to be clear what materials are being used as air seals, particularly around doors and windows, and what is being utilised as the vapour control layer. These may be the same or different depending on the design and performance required.
5. Work with the M&E engineerClose liaison is also required with the mechanical and electrical engineer on all but the simplest of projects. This is because the building’s systems have a fundamental part to play in energy use and are becoming increasingly sophisticated. Use of condensing boilers, under-floor heating, night purging to cool the building mass and intelligent facades are a few examples of good practice.
Many projects now consider the use of some form of solar collector, rainwater harvesting and even wind generation. It is clear that the payback period is long for photovoltaic panels, making it difficult to justify its viability while energy outputs are so low and the costs so high. Thermal solar collectors, on the other hand, provide a very useful energy input for comparatively little cost.
6. What about green features?
7. Think about your glazingThe energy performance of glazing, particularly if south or north facing, can be considerable. New types of glass with up to 13 coatings that reject low-frequency heat but let light through are now available. The combination of energy-saving low-emissivity coated glass and edge seals with low thermal conductivity are achieving very good U-values (in the region of 1.2 W/m2K). This is still 10 times more conductive than unglazed areas, though, so snug-fitting thermal blinds are a practical solution. Insulation embedded in the floor and at cold bridges is also a good way to improve performance. Most heat escapes through large glazed external surfaces and at the corners, so concentrating on these areas will improve performance.
8. Stay cool without air-conditioningWith potentially warmer summers, we should be considering how to keep building occupants cool without recourse to energy-intensive air-conditioning. Use of the building’s form to draw in air currents, ideally over water, can provide an attractive feature and achieve a significant amount of cooling. Adequate shading can be created by the roof or architectural features such as brises-soleils.
9. Retrofitting old buildingsA big problem is energy-inefficient existing building stock, as significantly improving the energy performance of an existing building can be difficult. However, overcladding the walls with insulation and render can be very successful. Overlaying flat roofs with insulation and a single-ply membrane is effective, too, and pitched roofs can be improved by installing prefabricated insulation panels, leaving just the tiles to be installed. New windows may be expensive but are straightforward to install. The British Fenestration Rating Council’s new scheme (see www.bfrc.org) for grading windows in the same way that white goods are rated makes the process very straightforward.
Remember, all windows are now subject to Part L of the Building Regulations.
10. Whole building calculationThe move towards whole building calculation methods of energy use means analysis of energy performance is becoming more complex for the specifier. Specifiers should make a start on understanding what is involved now.
11. Keep abreast of technological advancesLook out for new materials, including foils and multilayer sheets, low-density foams such as nanofoam, more sophisticated coatings and hybrid insulation products such as vacuum-sealed panels. However, it is important to be aware that the thermal analysis of these products is still not necessarily carried out very well.
Standards and Quality in Development: A Good Practice Guide, published by the National Housing Federation, which also produces a range of other useful guides.
The Housing Corporation also produces a range of useful literature.
Subject guides similar to this are available from Barbour Index as part of its Construction Expert and Specification Expert services.
For further information contact Barbour Index on 01344-899280 or visit www.barbour-index.co.uk