Possible Future Performance Standards for Part L outlines measures the construction industry could take to cut energy use. For specifiers of cladding and sports facilities there is plenty to mull over, including the following statements taken from the report:
"Energy or carbon calculation methods in SAP should be used as the basic method for establishing what is reasonable"
The move to a SAP-style rating is in part driven by a new EU directive on the Energy Performance of Buildings due in January 2006, which the UK must incorporate into law. One requirement is for a methodology to be adopted for calculating the overall energy performance of buildings which will encompass HVAC and low-carbon/zero carbon systems.
A move to whole building standards means that precise U-value targets are less significant. There will be less onus on the elemental method of compliance although designers will have to match a worse allowable U-value for each element. The document suggests that the worst allowable U-value will be 0.7 W/m2K for exposed walls and 3.3 for wood/PVCu/ metal windows and glazed doors. The elemental method of compliance will still exist though, and U-value standards will be improved in 2005.
"Consideration is being given to a legal requirement to carry out pressure-testing"
To improve the levels of airtightness the government is suggesting that more buildings undergo pressure testing. It says that non-dwellings with floor areas of more than 200 m2 should be tested (current guidance is to test buildings of more than 1000 m2). For dwellings, the report says that where robust details or third party quality assurance schemes are not used, housebuilders will have to pressure test homes. The paper says that tests could be made compulsory if it is found that robust details are not delivering the required standards.
"[There is a need for] improved correlation between design and as-built performance"
The government is considering two measures to improve workmanship on site:
- Increase the type and frequency of pre-completion testing to check that build quality matches the design brief.
- Base the performance standards on more realistic assumptions about build quality. This means that to achieve a given U-value more insulation might be required to compensate for defects in a typical construction. Builders who can demonstrate that their construction methods or systems deliver better build quality than the standard could use this to justify reducing insulation thickness.
"New airtightness standards could be justified for adoption in 2005"
Airtightness standards are likely to be improved and the government is considering adopting the following standards for different building types: The report says that the level of improvement will be more likely for energy-intensive buildings (such as balanced mechanically ventilated dwellings).
"We are giving consideration to whether standards could be defined for swimming pools and hot tubs"
The government is looking at what other elements within buildings might provide opportunities for reducing carbon emissions. The report says that swimming pools and hot tubs are particularly suited to the application of no/low carbon systems such as solar water or combined heat and power systems.
"Current thinking is that the effects of thermal bridges should be quantified as part of the overall assessment of whole building energy performance"
The issue of thermal bridging is one area that the government is looking at improving. New European Standard EN 14683, quantifying the effects of thermal bridging, will allow thermal standards for the building envelope to be measured. The report says that if the thermal bridging in design details are quantifiable and proven to perform well, they could be offset against poorer standards in the main elements of construction.
Working panels involving more than 250 building professionals are now considering the proposals and will report their findings to the Building Regulations Advisory Committee in the spring. BRAC will in turn recommend to the government what measures should be included in the Part L consultation paper, which is due to be published in June this year. The working panel meeting notes can be obtained from www.odpm.gov.uk.
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For more on the likely impact of the Part L proposals, see Building, 13 February, pages 55-57.