The Department of Energy and Climate Change (DECC) launched this month a consultation on the Standard Assessment Procedure (SAP), the main overarching calculation tool for demonstrating compliance to Part L for new build dwellings.
The consultation aims to set out the changes being proposed to improve the accuracy of SAP assessments, which underpin many other environment related policy initiatives such as Energy Performance Certificates and the Carbon Emission Reduction Target. SAP is being revised to tie in with the next revision of Part L, due for publication late 2009, for implementation in April 2010. Comments on SAP are invited by 12th August 2009 and the final version is expected to be published in the fourth quarter of this year.
TRADA Regulations Consultant Rupert Scott said, ‘We do believe that the changes will be very positive, but they will impact on the timber frame industry. We are therefore planning to stage a workshop for members, in partnership with designers who have a comprehensive working knowledge of SAP, to appraise the effect of the proposed changes.'
He added, ‘As we design buildings with much improved thermal efficiency, it is generally accepted that the current version of SAP (2005) becomes increasingly flawed. SAP is principally a regulation tool, rather than a design tool. It is expected to calculate the right results at the levels of performance set in the current Building Regulations / Part L. Broadly speaking, it has delivered this, although many might argue against this point! However, it is not sufficiently robust or sophisticated that it can deliver "correct" results at higher levels of thermal performance.'
Changes are being suggested and opinions sought in a number of key areas:
Monthly calculations
Calculations to be performed for each month, rather than for four seasons. This should lead to a more accurate calculation of the energy balances (heat losses and gains).
Updated weather
The current data originates from 1960s and 1970s and it would therefore seem reasonable to use up-to-date weather records. The consultation asks whether regional data should be used, which will make quite a difference in some areas. The question is also raised whether we should predict the climate going forward, ie consider designing for possibly hotter conditions.
Boiler efficiency figures
Independent measurements of boiler efficiency levels are consistently lower than those declared by boiler manufacturers. The proposal is to address this.
Inclusion of thermal mass and cooling calculations
Part L requires that a fairly simple calculation is performed to estimate the likelihood of overheating in the warmest summer periods, to check if it might be too high. The draft revision will for the first time take account of thermal mass. An equation for calculating the ‘thermal mass parameter' has been proposed, plus a table (1C) of common construction materials and their thermal capacity values, required for the formula. TRADA believes that this is certainly something for the timber frame sector to watch carefully and aims to attend workshops where the newly proposed formulae will be trialled, to see what effect it has.
Hot water
Once buildings achieve very high levels of energy efficiency in terms of their fabric, hot water becomes the most significant energy-consuming element. Consequently the assumptions made about hot water demand and energy characteristics have been revisited.
Email if interested in participating in TRADA's SAP workshop as tutor or delegate. More details will be released in the near future.
