Extension Calculation
Expert Compliance for UK Extensions Since 2005
When designing a new extension with large areas of glass or removing existing doors to a conservatory, you must demonstrate compliance with Approved Document L (Volume 1: Dwellings). At Crowther Solutions Ltd, we specialise in Extension SAP Calculations, providing the technical modelling required to justify high levels of glazing while meeting energy efficiency targets.
The "Notional vs. Proposed" Approach
Under current Part L1B regulations, glazing is typically limited to 25% of the new floor area. If your design exceeds this, we use the SAP 10.2 methodology to model two versions of your project:
The Notional Extension: A baseline model built to minimum standards with the 25% glazing limit.
The Proposed Extension: Your actual architectural design with the desired glazing and specifications.
By demonstrating that your Proposed design produces fewer CO2 emissions than the Notional model, we can achieve Building Control approval for even the most ambitious glazed designs.
What Our Service Includes:
Proposed & Notional SAP Modelling: Accurate data comparison to prove compliance.
U-Value Calculations: Precise analysis of walls, floors, roofs, and high-performance glazing.
Expert Specification Advice: If your initial design doesn't hit the target, we provide practical solutions and insulation upgrades to bridge the gap.
Easy-to-Follow Written Summary: A clear report for your Building Control officer.
Why Partner with Crowther Solutions?
With 20 years of experience, we understand the nuances of extension compliance. We typically model the Extension Only, which is widely accepted by Building Control and saves you the cost and time of surveying the entire original house.
Get a Quote for Your Extension
Direct Technical Support: 07814 462828