Part L
Energy and SAP calculations
Design-stage and as-built SAP calculations for new and converted homes, with the EPC lodged at completion.
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Energy & performance calculations
Thermal bridging and psi-values
A qualified thermal modelling specialist models the heat loss at key junctions, such as wall to floor and around openings, to calculate psi-values to BRE BR 497. Your energy assessor can then use them in SAP instead of default values.
When you need it
Heat escapes faster at junctions than through plain walls. Where calculated values are not available, the SAP calculation uses default values, which are often less favourable. Approved Document L allows construction joint details calculated by a suitably competent person following BRE BR 497.
Calculated psi-values are optional, but they can improve the SAP result or allow a less onerous fabric specification. The temperature factor from the same model also shows the surface condensation and mould risk at each junction.
What is included
Included
- Review of the junction details and drawings
- Numerical modelling of each junction to BR 497 conventions
- Psi-values and temperature factors for each junction
- Results set out for your SAP or SBEM assessor
Priced separately
- SAP or SBEM calculations
- Redesign or redrawing of details
- Photographic evidence of the built details
- Remodelling after details change
Your written quotation confirms the exact scope, what is included and any limits for your building.
What you receive
A thermal bridging report listing each junction with its psi-value and temperature factor, ready to enter in the energy calculation.
Sent as a PDF. We can send it to your building control body or agent on request.
Our reports and testing support the compliance process. Approval and completion decisions remain with your building control body: the local authority, a registered building control approver, or the Building Safety Regulator for higher-risk buildings.
How to prepare
- Large-scale junction details, with dimensions
- Wall, floor and roof build-ups and products
- A list or marked-up plan of junction types and lengths
- Your SAP assessor’s contact details
- Any manufacturer psi-values you already have
Send what you have. Missing details will not stop an enquiry; we will tell you anything still needed.
How it works
Tell usChoose the service or describe the job.
Written quotationScope, deliverables and price, confirmed in writing.
We manage the workArranged and coordinated by RegulaBuild. Technical work is carried out by appropriately qualified professionals.
Your reportThe output named in your quotation, with any follow-up.
Questions
Do I have to calculate psi-values?
No. SAP can use default values. Calculated values are a choice that often improves the result.
What is a y-value?
It summarises the heat loss from all junctions across the whole building. It is worked out from the psi-values and the junction lengths.
Do the built details need checking?
Yes. For new homes, Approved Document L asks for photographs showing the details were built as designed. We offer that as Part L evidence support.
Often booked with
Combine them in one quote request
Part L
U-value calculations
Heat-loss calculations for walls, floors and roofs, so the specification can be checked before build.
Energy calculationsView service
Part L
Part L evidence support
Photographic evidence and the BREL report, gathered during the build and issued at completion.
Energy calculationsView service
Where we work
Thermal bridging and psi-values across England
Request a quote
Discuss thermal bridging and psi-values
Start with this service and add anything else you need. If you are unsure, say so and we will advise.