The Zero Carbon Hub is running a collaborative industry led programme examining the discrepancy between design and as built energy performance for new homes. This session will examine the latest evidence and conclusions from this research. It will highlight issues that influence the performance gap and explore ways to reduce this including the application of rigorous quality assurance processes.

1. Design vs As-built
Evidence Review
Ian Orme
Sustainable
Construction Group
BSRIA

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3. Evidence Gathering
Aims
• Understand where the gaps in the development
process occur,
• Reflect performance issue for dwellings constructed
to meet current Regulation requirements,
• Review different scale developments and developers,
• Develop a prioritisation matrix to help focus and
prioritise possible solutions
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4. Evidence Gathering
• Literature review
– 100+ reports and documents reviewed to date
• Housebuilding process review
– Nine developments covering 1,000 plots
– On-going work
• SAP audits and questionnaires
– Review of as-designed and as-built SAP
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5. Literature Review
• State of the Industry
– Aggregated data from NHBC, LABC, professional
institutions, house builders, manufacturers
• Compliance Processes
– As-built SAP ratings, Air Permeability tests results, use of
ACD/ECD, Commissioning Test Results
• Field Trials
– EST Heat Pump report, TSB BPE programme
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6. Literature Review
• Academic Studies
– Stamford Brook, Elmtree Mews, Temple Avenue
• “Secret” knowledge
– Manufacturer’s field trial data, unpublished academic work
• Anecdotal
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7. Literature Review
5%
Evidence type
5%
10%
35%
45%
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Guidance
Manufacturers
Field Trials
Academic Studies
Site visits (inc TSB)
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8. Housebuilding Process Review
• Approach
– Information gathering followed by semi-structured
interviews
– Design review
– Construction site walkthroughs
• Developments volunteered by housebuilders
– Nine completed to date
– Have tended to be volume builders, but ‘pot’ is increasing
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9. SAP Review
• Three stage approach:
– Review of original design stage assessment as
provided by the developer,
– Recalculation of the design stage based on the design
information provided for the process review,
– Calculation of as-built SAP based on site inspection
and interview findings. Comparison with developer
provided as-built SAP, if available.
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10. Synthesizing the Findings
• Approx. 50 issues identified across the Working
Groups
• Frequency with which each issue occurs in the
dataset
• Nature of the source data: peer reviewed academic
paper; journalistic article, ‘hear say’
• Evaluation by review group of impact across a range
of deliver models (volume, small scale and traditional
contracting)
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11. Literature Review Number of Sources Referenced by Issue Area
100
90
80
70
60
50
40
30
20
10
0
Concept &
Planning
Detailed Procurement Construction Verification
design
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Testing
Energy
Overarching
Modelling
Tools
Good
Practice!
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12. Literature Review Number of References by Issue Area
1200
1000
800
600
400
200
0
Concept &
Planning
Detailed Procurement Construction Verification
design
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Testing
Energy Overarching
Modelling
Tools
Good
Practice!
12

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15. The Matrix
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23. Illustration of Findings
• Integration of design
– Focused on architectural layout and optimisation of
space
– Increases complexity of geometry with ‘knock-on’
impact to structural requirements, increasing thermal
bridging
– A near complete absence of an engineering approach
to services design with resulting problems in
installation and commissioning
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24. Illustration of Findings
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25. Summary
• Evidence review has established 15 clear issues that
are demonstrated to impact the performance gap
• These encompass, knowledge and skills,
communication and responsibility for the energy
performance
• Broad themes and findings similar to wider TSB BPE
work
• Developing strategy for Priority for Research in next
phase of project
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26. Design vs As-built
Evidence Review
ian.orme@bsria.co.
uk