26/09/2025
Extensions - What we do and what do you get for your money?
SAP Calculations – Overglazed Extensions
In Building regulations home extensions are approved under Approved Document L, if they are built within certain U‐Value Parameters and the Glazing Area does not exceed 25% of the New Floor Area. If your requirements are outside of these constraints, we can help prove that the extension built as you would like, is better than the requirements of the Regulations.
There are 3 methods of compliance;
(1) proving the 25% rule.
(2) Area Weighted Calculation.
(3) Full Comparison Calculation.
Each have a different price – we will only ever charge you the minimum required.
• We calculate the SAP and advise you on how to achieve a pass under Building Regulations We provide the U Values at no extra charge.
• Part G – Internal Water Consumption Calculations
• We can supply you with a basic specification at design stage to give you targets when purchasing the internal water fittings (Flow restrictors for Taps and Showers, Bath size to overflow and Dual flush rates for toilets).
• When built we can supply the Final Certificate for your BCO and get this element signed off quickly.
• Please provide details of any further reductions required to satisfy any planning conditions.
If you’re planning an extension, garage conversion or internal alterations, Building Regulations are just as important as planning permission — and often the real gatekeeper to getting work started on site.
Quick summary:
Considering a home extension? Before you break ground on your project, it’s essential to navigate the somewhat murky waters of planning permission. While the idea of expanding your living space is exciting, the legalities can be daunting. Whether you’re dreaming of a new kitchen, a sunroom, or a two-storey addition, understanding when you need permission and the costs involved is crucial.
Understanding Planning Permission: What You Need to Know:
Planning permission means getting formal approval from your local planning authority before beginning your project. This ensures your extension complies with building standards and local policies. Without it, you risk enforcement action or even demolition.
Note: Planning permission and Building Regulations approval are different. Many projects require both.
Types of Home Extensions That Require Planning Permission:
You will usually need permission if your extension:
• Exceeds permitted size or height limits
• Is in a conservation area or attached to a listed building
• Creates new dwellings or alters the property’s use
• Significantly impacts neighbours or the street scene
Common Home Extensions That May Not Need Planning Permission:
Some projects fall under Permitted Development rules. Examples:
• Small rear kitchen extensions
• Loft conversions that don’t alter the roofline
• Garden outbuildings (subject to limits)
Tip: Even when planning permission isn’t required, check whether Building Regulations or restrictive covenants apply.
The Planning Permission Application Process Explained:
The process typically involves preparing planning drawings, submitting via the Planning Portal, paying the relevant planning permission cost, and awaiting council consultation and decision.
Key Factors Influencing Planning Permission Decisions
• Impact on neighbours (light, privacy, noise)
• Aesthetic fit with surroundings
• Environmental considerations (flood risk, biodiversity)
Pre-app advice: Councils often offer pre-application services—these can de-risk your submission.
Consequences of Building Without Planning Permission:
Ignoring the rules may lead to enforcement, fines, and even demolition. It also affects your property value and can block future sales. Retrospective applications are possible but risky.
Important: Prevention is always better than cure—know do I need planning permission for an extension before you start.
Tips for a Successful Planning Permission Application:
• Use clear drawings and professional support
• Respect neighbours and reduce objections
• Include sustainable features
Alternatives to Planning Permission: Permitted Development Rights:
Some single-storey rear extensions or lofts fall under PD.
Conclusion: Navigating the Planning Permission Landscape for Your Home Extension:
Securing approval can seem daunting, but with clear information, accurate drawings, and a professional approach, it’s manageable.
Contact us, we would be happy to help.
