If you're planning an extension or conversion to your property, it's important to bear in mind the amount of glazing used and whether this exceeds government regulations, as this may mean that you need to get SAP calculations completed.

If you're on the hunt for a specialist team that can take care of this for you, Falcon Energy are your answer. With many years of experience and a professional, dedicated team of experts, we guarantee great service, extensive knowledge, and speedy results.

SAP 10 & SAP 2012

We are able to provide both SAP 10 and SAP 2012 calculations for energy ratings of dwellings. Please note that SAP 2012 is only applicable for buildings with an application and work commencement date before 15th June 2022.

What are SAP calculations?

When a property undergoes changes such as the addition of an extension or conversion to an existing building, it is necessary to seek approval from the local planning authority for planning permission based on Building Regulations. During the design stage of your project, SAP calculations must be conducted to support the application for Building Regulations approval.

The results of the SAP calculations, including the energy rating, help demonstrate that the proposed development meets the necessary energy efficiency standards. By conducting these calculations during the design stage, you can identify areas where improvements can be made to enhance the energy efficiency of the property and potentially reduce energy consumption.

It is worth noting that SAP calculations may also be required at various stages throughout the building process for compliance checks, such as during the submission of Building Regulations applications or for final assessments upon completion. However, the initial calculations during the design stage are crucial for informing and guiding the construction process. This allows building work to begin with Building Regulations approval from the local authority.

Why do you need SAP calculations for extensions and conversions?

If you're planning on extending or converting your property, you will need to ensure that the new elements meet the required energy efficiency standards. SAP calculations can help you to achieve this by identifying areas where improvements can be made. They can also help you to comply with Building Regulations and obtain an Energy Performance Certificate (EPC). Once the local planning authority have permitted development, most extensions are compliant with Building Regulations.

Building Extension

How do SAP calculations work?

These calculations consider various factors including insulation, heating systems, and ventilation, resulting in a numerical rating ranging from 1 to 100. A higher rating indicates a more energy-efficient property.

What is involved in the SAP calculations process?

The process involves several key steps:

Building Geometry

The first step is to gather information about the building's geometry, including the floor area, volume, and dimensions of each space within the dwelling.

Fabric and Insulation

The next step is to collect data on the building fabric, such as the insulation levels of walls, floors, and roofs. This includes details about the type and thickness of insulation materials used.

Windows and Doors

Information regarding the windows and external doors is collected, including their dimensions, U-values (thermal transmittance), and solar heat gain properties.

If the building has double glazing, the U-values of the double glazed units are considered. These values represent the heat loss through the windows. The lower the U-value, the better the thermal insulation provided by the double glazing. A key method of calculating the thermal values of windows and doors is the Excess Glazing Calculation.

The solar heat gain through the windows is also assessed. This involves considering the orientation of the windows, the shading provided by external elements, and the solar heat gain coefficient (SHGC) of the windows. SHGC represents the amount of solar radiation that passes through the window and contributes to heat gain inside the building.

Heating Systems

Details about the heating system(s) in the building are gathered. This includes the type of system (e.g., boiler, heat pump), fuel source, and efficiency ratings. Additionally, the controls and timers associated with the heating system are taken into account.


The ventilation method and system used in the dwelling are considered. This includes information about the ventilation rate, whether it's provided naturally or mechanically, and any heat recovery systems in place.

Hot Water Systems

Data about the hot water system(s) is collected, such as the type of system (e.g., combi boiler, immersion heater), fuel source, and efficiency ratings.

Renewable Technologies

If there are any renewable energy technologies installed, such as solar panels or heat pumps, their details are included in the calculations.

Occupancy Patterns

Information about the occupancy patterns and usage of the building is considered, including the number of occupants, their behaviours, and any special requirements.

SAP Calculation

Based on the collected data, the SAP calculation software is used to process the information and generate an energy performance rating for the dwelling. This rating is represented as a numerical score known as the SAP rating, as well as an energy efficiency band (A to G).

The SAP calculations provide an overall assessment of the energy efficiency and environmental impact of the dwelling, taking into account factors such as heat loss, heat gain, energy usage, and carbon emissions. The results can be used to determine compliance with Building Regulations, provide recommendations for improvements, and assess the impact of proposed changes to the building's energy performance.

What are Excess Glazing Calculations?

With new extensions or conversions to a property, there's a limit to the amount of glazing permitted. You're restricted to 25% of glazing to floor area and if you exceed this limit, you must have proper and professional justification. This is due to glazing and openings losing more heat than walls, making it less energy efficient.

With many extensions these days having far more glazing on elements to let in more light, sticking to the 25% limit can be difficult. Excess Glazing Calculations can successfully prove your need for extra glazing and help keep your building project on track and on budget.

If it's deemed that your new extension or conversion exceeds regulations in terms of glazing, the Building Control Officer will ask to see official Excess Glazing Calculations that must demonstrate either:

  • Area weighted U-value method
  • Full SAP calculation to include the existing property

The first option is typically suited for property renovations that only accrue a small amount of excess glazing which, in turn, shows the thermal elements could potentially be improved elsewhere to compensate.

Should the total percentage of excess glazing be recorded as higher, a full SAP calculation is required that must also take into account your existing property. This assesses the overall energy performance of your home, taking into account building materials and heating systems. Depending on the results, the rest of your current property may be taken into account and it may be suggested that upgrades elsewhere would successfully offset any additional glazing needed for the new build.


In order for us to undertake excess glazing calculations accurately and efficiently, we need the following details from you:

  • Construction drawings to scale
  • Existing and proposed floor plans
  • Existing and proposed elevations
  • Any heating systems to be used
  • Any renewable energy sources (such as solar panels)
  • Existing and proposed sections
  • Site location

We will use all of this information to put the calculations together and understand how your extension will impact the efficiency of your home, if at all.


At Falcon Energy, not only do we have years of experience at providing Excess Glazing and SAP calculations but we also pride ourselves on outstanding customer service and fantastic, speedy results. We know that time is often of the essence in extension or conversion cases and are keen to keep your project on time and budget. We'll work hard to complete the work as quickly as possible, without compromising quality, and are locally based in Horsham, West Sussex, meaning we could get to you sooner than you think. We work throughout Sussex, Surrey, Kent and London.


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Call us now for a no obligation quote

Our team at Falcon Energy are here to help and would love to offer you a free, no obligation quote for your SAPs and Excess Glazing Calculation needs. Just call us today on 01403 253439 or email info@falconenergy.co.uk and we'll be happy to help.