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Overglazed Extension Calculations

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SAP Calculation For Over-glazed Extensions

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Don't Make Costly Mistakes with Your Overglazed Extension. Get Expert SAP Calculations.

Highly glazed extensions can be tricky when it comes to Building Regulations. Our team of SAP Assessors specializes in these complex projects, ensuring your design meets Approved Document L without compromise. With years of experience and a 100% compliance record, we take the stress out of SAP calculations. Get a free consultation today.

What is an Overglazed Extension Calculation?

Overglazed extensions, with their expansive windows and walls of glass, are a popular way to bring natural light and a sense of spaciousness into a home. However, these beautiful designs can present unique challenges when it comes to meeting Building Regulations. A key concern is energy efficiency: all those windows can lead to significant heat loss. This is where SAP (Standard Assessment Procedure) calculations come in.  

Because overglazed extensions have a higher proportion of glass than typical extensions, they require a specialized type of SAP calculation. This calculation focuses on demonstrating that the extension, despite its large glazed area, won’t negatively impact the overall energy efficiency of the home. It often involves showing how other energy-efficient features compensate for the increased heat loss through the windows. This could include things like:

High-performance glazing:

Using windows with excellent insulation properties (low U-values).  

Enhanced insulation:

Adding extra insulation to walls, roofs, and floors.

Efficient heating systems:

Installing modern, energy-saving boilers or heat pumps.

Solar gain:

Taking advantage of the sun's heat through south-facing windows (while managing overheating).

Do You Need an Overglazed Extension Calculation?

Whether or not you need a SAP calculation for your overglazed extension depends primarily on how much glazing you have. Building Regulations (specifically Approved Document L: Volume 1) generally allow for glazing up to 25% of the new floor area of the extension (plus any existing windows that are replaced). If your design stays within this limit, a full SAP calculation is usually not required.   

However, as many homeowners desire more glass than this, it’s common for extensions to exceed the 25% limit. In these cases, you’ll likely need a SAP calculation to demonstrate compliance with Building Regulations. This calculation proves that the overall energy performance of your home, including the overglazed extension, is no worse than if you had built a more conventionally glazed extension. This is often referred to as the “design flexibility” option within the regulations.

Even if your extension was built years ago, you might still need a SAP calculation. If you’re selling your home, solicitors often request proof of Building Control sign-off, which may require demonstrating compliance with the regulations that were in effect at the time of construction. This is where past SAP calculations become crucial.

 

How Does a SAP Assessment Work?

Essentially, a SAP assessment compares your proposed extension to a “notional” extension – a hypothetical extension built to the minimum standards of the Building Regulations. This comparison helps determine whether your design meets the required energy efficiency levels. There are a few different approaches to demonstrating compliance, and the best option for you will depend on the specifics of your project.

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3 SAP Calculation Options Armeec Offers

The core goal of a SAP assessment is to show Building Control that your extension won't lead to excessive carbon dioxide emissions. Since glass transfers heat more readily than insulated walls, extensions with a lot of glazing can be a concern. But there are ways to achieve compliance, even with a beautifully overglazed design.

Here’s a breakdown of the three main SAP calculation options we offer:

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Option 1

Element-Based U-Value Comparison

This method is the most straightforward approach and is often suitable for extensions where the glazing area is only slightly over the permitted limits. It focuses on the individual components of your extension.

How it Works:

  • We meticulously analyze the U-values (a measure of heat transfer) of each element of your proposed extension – the walls, roof, floor, and, of course, the windows.
  • We compare these individual U-values to the minimum standards set by Building Regulations.
  • We also verify that the total area of windows and doors in your extension doesn't exceed the allowed limit relative to the extension's floor area and any pre-existing openings covered by the extension.

When it’s Right for You:

This option is typically the best choice when your extension design is already quite close to compliance and only slightly exceeds the glazing allowance. It’s less complex than the other options and can often be a quicker and more cost-effective way to demonstrate compliance.

What You’ll Receive:

A comprehensive report detailing the U-values of each element of your extension, demonstrating how they meet or exceed the required standards, along with an analysis of your window and door area. This report is ready for submission to Building Control.

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Option 2

Area-Weighted U-Value Comparison

This method offers more flexibility than Option 1, as it considers the overall thermal performance of the extension rather than focusing on individual elements.

How it Works:

  • We calculate the average U-value of your entire extension, taking into account the size and performance of all its components, including the glazing.
  • We then compare this average U-value to that of a "notional" extension – a hypothetical extension of the same size and shape as yours, but built to the minimum regulatory standards with the standard 25% glazing allowance.
  • If the average U-value of your proposed extension is as good as, or better than, the notional extension, your design meets the requirements.

When it’s Right for You:

This option is suitable when your extension slightly exceeds the glazing allowance and you want to balance the performance of different elements. For example, you might have a larger glazed area but compensate with higher levels of insulation in the walls or roof.

What You’ll Receive:

Area-weighted U-value reports for both your proposed extension and the notional extension, demonstrating the comparison and proving compliance. These reports are ready for submission to Building Control.

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Option 3

Whole Dwelling Calculation

This is the most comprehensive approach and is necessary when your extension design significantly exceeds the glazing allowance or when the area-weighted methods don’t demonstrate compliance. It considers the energy performance of your entire home, including both the existing structure and the proposed extension.

How it Works:

  • We create a detailed energy model of your entire property, both with your proposed extension and with a "notional" extension attached.
  • We use specialized software to calculate the predicted annual carbon dioxide emissions for both scenarios.
  • We compare the emissions: if your home with the proposed extension performs as well as, or better than, the notional scenario, you've met the requirements.

When it’s Right for You:

This option is essential for heavily glazed extensions or when other methods fail to demonstrate compliance. It allows you to offset the impact of the large glazed area by making improvements to the energy efficiency of your existing home.

What You’ll Receive:

Comprehensive SAP calculation reports for both your actual property (with the proposed extension) and the notional property (with the notional extension), along with a U-value report. These reports are ready for submission and provide a complete picture of your home’s energy performance. We will also advise you on any further steps needed to achieve compliance.

Let's Discuss Your Project!

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Why Do We Succeed

How we carry out Calculations for overglazed extension?

01
Initial Consultation & Quote
We start by discussing your dream extension. We'll review your plans, focusing on the glazing, and provide a tailored quote for your overglazed extension's SAP calculations.
02
Plan & Specification Review
Share your design details. We'll provide a simple questionnaire focusing on the specifics of your overglazed extension, including window types, sizes, and placement.
03
SAP Design Stage Calculations
Our expert assessors will perform detailed calculations, addressing the unique challenges of overglazed designs. We'll identify potential areas for optimization to ensure compliance with Building Regulations.
04
Compliance Guidance & Recommendations
If needed, we'll offer tailored advice to maximize energy efficiency without sacrificing the aesthetic you desire. We understand the balance between light and performance in overglazed extensions.
05
As-Built SAP Calculations & EPC
Post-construction, we'll conduct final calculations reflecting the built reality of your overglazed extension and generate your Energy Performance Certificate (EPC).
05
Document Delivery & Support
We'll provide all necessary documentation, including the SAP report and EPC, ready for submission to Building Control. We're here to support you throughout the approval process, ensuring your overglazed extension meets all requirements.

Why We're the Right Choice for Your Overglazed Extension Project?

Proven Success

5,000+ extensions, 100% pass rate. Our experience ensures compliant results for your overglazed extension.

Maximize Glazing

Keep your vision, we’ll find a way. We’ll work to retain all the glazing in your dream design.

Cost Effective

Save on builds, not compliance. We’ll guide you to the most affordable path to energy efficiency.

Guaranteed Results

No pass, no fee – our commitment. We’ll support you until your overglazed extension achieves compliance.

Fast & Flexible

24-hour service available. Need it urgently? We offer expedited service for time-sensitive projects.

Frequently Asked Queries About Overglazed Extension Calculation

Is a site visit required?
No, a site visit isn't needed. We can complete the SAP calculations using your architectural drawings and specs for materials and technology—everything is done remotely.
What info is needed for SAP Calculation on Extensions?
We’ll need: Architectural drawings (plans, elevations, cross-sections) Material specs Details on windows, doors, and heating systems Ventilation info (if any) Renewable energy details (if applicable) Lighting info (internal and external) For overglazed extensions, glazing specs.
What happens if my design fails its SAP Assessment?
If your design fails, you'll need to revise it to meet the requirements. Depending on the changes, you might need a re-assessment or additional testing. The SAP Assessor will guide you through the necessary steps, especially for overglazed extensions.
Do I need a SAP Calculation for an extension?
You’ll need a SAP Calculation if the glazed area exceeds 25% of the floor area, including any openings affected by the extension.
Can I do a SAP Calculation?
SAP Calculations must be done by a certified On Construction Domestic Energy Assessor (OCDEA) who is accredited and regularly audited.
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Registered Address
Dalton House, 60 Windsor Avenue, London, SW19 2RR
Trading Address
Dalton House, 60 Windsor Avenue, London, SW19 2RR
Contact Number
+44 7816 587548
078-165-87548
Email Address
info@armeec.co.uk