What is Over-glazed extension compliance?

Over-glazed extension compliance ensures that extensions with a glazing area exceeding 25% of the floor area of the extension are not materially ‘worse’ than a notional extension, as defined under Part L. These assessments are required to demonstrate that the additional glazing won’t lead to excessive heat loss or overheating and are compliant with modern construction standards. This is typically demonstrated via SAP calculations, comparing the proposed design against a notional compliant extension. The goal is to ensure the increased glazing does not compromise thermal performance or contribute to overheating, and that the overall extension meets or exceeds regulatory standards.

Why Over-Glazing Matters:

Heat Loss:Glass is a poor insulator compared to walls, so excessive glazing can lead to more heat escaping the house, especially during colder months. 

Increased Carbon Emissions:The increased energy consumption to maintain a comfortable temperature in an over-glazed extension can lead to higher carbon dioxide emissions. 

Building Regulations:Building Regulations Part L (Conservation of Fuel and Power) aims to minimize energy consumption in new and extended buildings. Over-glazing can make it difficult to comply with these regulations. 

How to Achieve Compliance with Over-Glazing:

SAP Calculation:If the extension exceeds the 25% glazing limit, a Standard Assessment Procedure (SAP) calculation may be required to demonstrate compliance. SAP calculations assess the overall energy performance of the house, including the extension, and ensure it meets the required energy efficiency standards. 

Compensatory Measures:Other ways to achieve compliance include increasing insulation elsewhere in the house, upgrading the heating system, or using more efficient glazing materials. 

Area-Weighted U-Value Calculation:Another approach is to demonstrate that the over-glazed extension doesn’t increase energy loss above that of a conventionally glazed extension using an area-weighted U-value calculation.