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
Water efficiency calculations
A qualified energy assessor calculates the expected water use of each new home with the government water efficiency calculator, or checks it by the fittings approach, so you can show the 125 litre standard, or 110 litres where planning requires it, is met.
When you need it
Regulation 36 limits the potential water use of a new home to 125 litres per person per day. Where the planning permission sets the optional requirement as a condition, the limit is 110 litres. Homes formed by a material change of use are not covered by regulation 36.
Approved Document G sets out two ways to show compliance: the water efficiency calculator, or a fittings approach with maximum flow rates and capacities. The person carrying out the work must tell building control the result no later than five days after completion, so the calculation should reflect the fittings actually installed.
What is included
Included
- Design-stage calculation for each house type
- Schedule of the fitting flow rates and capacities the result relies on
- Advice on fittings where the target is missed
- Final calculation using the installed fittings, for the building control notice
Priced separately
- Supply or installation of fittings
- Rainwater or greywater system design
- Recalculation after fittings change on site
Your written quotation confirms the exact scope, what is included and any limits for your building.
What you receive
A water efficiency calculation for each house type, showing litres per person per day against the 125 or 110 litre target, with the figures needed for the notice to building control.
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
- Number of homes and house types
- Planning permission and any water efficiency condition
- Specification of WCs, taps, showers and baths
- Dishwasher and washing machine details, if supplied
- Any rainwater or greywater reuse system
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
How do I know if 110 litres applies?
Check your planning permission. The optional 110 litre requirement applies only where a planning condition requires it.
Can I just use low-flow fittings?
Yes. The fittings approach lets you show compliance by choosing fittings within set limits. If any fitting is outside them, the calculator is used instead.
Is the 125 litre limit changing?
Government consulted in 2025 on lowering the limits. No change has been made yet, and we will apply whichever standard is in force for your project.
Often booked with
Combine them in one quote request
Planning
Sustainability statements
Statements covering energy, water, materials and waste for planning submissions.
Energy calculationsView service
Part O
Overheating assessments
Simplified method or dynamic modelling to show new homes and other new residential buildings limit overheating in summer.
Energy calculationsView service
Where we work
Water efficiency calculations across England
Request a quote
Discuss water efficiency calculations
Start with this service and add anything else you need. If you are unsure, say so and we will advise.