SAP Calculations for Extensions

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

SAP Calculations are very often required for extensions, especially if your proposal includes large areas of glazing.

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 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!

Would you like to discuss your project?

Call us for a chat on 01202 280062 or email

"I have to say that BE have been so pleasant to deal with and so competent at their jobs. As you know there are other firms doing this type of work but I am so glad that I chose Build Energy...I have nothing but praise for you. Thank you once again."

Stephen Aspinall

Oakwood Drive