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SAP Calculations for Extensions

We all want lots of light – and we all like lots of lovely glazing right?

Part L1b of the Building regulations requires that areas of new glazing should account for no more than 25% of new floor area. Of course, many extension designs will propose more than this, and therefore will not comply with this rule.

We can help you overcome this hurdle easily and quickly. SAP Calculations are produced by accredited energy assessors, and can be used to demonstrate how your proposal complies with building regs requirements, even with large areas of glazing.

SAP Calculations for Extensions – How Do They Work?

Glazing and openings lose more heat than walls and roofs, which is why the building regs set a limit. However by upgrading or over compensating in construction of other elements, or perhaps demonstrating additional, useful solar gains by virtue of that extra glazing, the negative impact of larger expanses of glass can be removed.

There are further options available to take account of upgrades to the existing property – especially useful if the dwelling is receiving a make-over too. We can guide you through all the options.

Many ‘change of use’ schemes will also be subject to SAP regulations, like flat conversions or commercial-to-residential conversions.

What Do We Need?

To carry out a full SAP L1b assessment, your assessor needs two things:

  • A set of existing and proposed plans, to scale
  • A summary of the intended construction and services details

The work is then carried out with a desktop assessment. We don’t need to come to site or carry out any surveys at all.

SAP Calculations For Extensions – Our Speciality

We carry out a large volume of SAP Calculations for extensions on a daily basis, and can provide you with all the help and guidance you need.

We’ve helped many hundreds of architects, contractors and homeowners all over the country and it is extremely rare that we do not find a solution – with no extra cost or change to your plans.

If required, we will even deal with your Building Control Officer, understand what is required, and take care of everything – Easy!

To find out more about conversions and extensions see Part L1b – The Info.

Would you like to discuss your project?

Call us for a chat on 0330 055 34 05 or email

Recent Projects

"As a design and build company, we have been using Build Energy as external consultants for the last two years and they have never failed us. Their friendly, easy going staff make our work easier. We are definitely looking forward to work with them in future projects".

Diego Sanz-Burgos
- EMD Group

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