Glazing SAP Calculations


SAP Calculations can be problematic for architects and clients alike, James Price Glazing can now help take this nightmare away. We provide SAP calculations for all our clients when required for both residential and commercial projects.

The SAP calculation is used to measure the energy efficiency of a property to check compliance with the Building Regulations L1A or L1B. It is from these calculations that the Energy Performance Certificate ( EPC ) is produced. An EPC is one of the documents that is required for building control sign off and is a legal requirement when a property is sold or rented.


Glazing is a major part of the SAP calculation and there is a lot to learn. This is why we work closely with Complete Sustainability Solutions one of the leading companies in the industry.

We can therefore provide a complete planning and design service to ensure your new bespoke glazing meets all the current building regulations.

A normal provision would be to limit the total area of windows, roof windows and doors so that it does not exceed the sum of:

a) 25% of the floor area of the extension

b) The total area of windows or doors which as a result of the extension no longer exist or area exposed.

Once you have chosen your glazing options we will start to plan your new project. The SAP calculation will be modeled with state of the art and Government approved accredited modelling software. Once the result is calculated we can then work with you to tailor the design.


You have chosen for us to install a glass box extension at the rear of your property which would take the overall glazed area of your property over the limit of 25% of floor area plus total area of windows removed.

Our specialists would then look at what adjustments can be made elsewhere in the property to achieve SAP compliance. You will receive SAP worksheets to confirm if compliance has been achieved which can be forwarded to Building Control.

Worries about overheating….

We can also assess whether the new glass box extension will cause overheating to the property. If it gets flagged up that overheating issues do arise, our specialist will advise what adjustments can be made to remove this issue by adding adaptions such as extra ventilation, air conditioning or even different coatings on the actual glass ensuring the SAP has passed and your property would neither overheat in the summer or require too much heating in the window.

For more details you can read more on SAP Calculations for Glazing Here

Here is a sample SAP Calculation you can view which was generated by our partner Complete Sustainability Solutions