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EXPLAINING WHY SAP CALCULATIONS ARE NEEDED FOR GLAZING OVER 25% IN EXTENSIONS

SAP Calculations are needed when excessive proposed glazing is added to extensions such as Bi-Folding Doors, Windows and Sky Lanterns

Discount Plans has put this article in place to explain and demonstrate what is required for Building Control to sign off your design proposal before the ordering of any external Windows or Doors to comply.

"DO NOT PURCHASE any external WINDOWS or DOORS prior to getting a SAP Assessor approval"

SAP (Standard Assessment Procedure) calculations are required to demonstrate compliance with Building Regulations Part L when a new extension includes glazing (windows, doors, or roof lights) that exceeds 25% of the extension’s total floor area. These calculations ensure the extension remains energy-efficient and does not negatively impact the overall energy performance of the dwelling.

When Are SAP Calculations Needed?
- New Extensions: If the glazing in your extension exceeds 25% of the total floor area.
- Conservatories/Orangeries: Glazing is often integral, requiring SAP calculations if insulation and energy efficiency could be compromised.
- Energy Compliance Check: Needed to prove the extension compensates for additional heat loss caused by the excess glazing.

How to Work It Out
1. Determine the Total Floor Area of the Extension:
   - Calculate the floor area (in m²) of the proposed extension.

2. Calculate the 25% Allowance for Glazing:
   - Multiply the total floor area of the extension by 0.25. This gives the allowed area of glazing.

3. Add Existing Dwelling Glazing Allowance (If Applicable):
   - For extensions affecting existing openings (e.g., when a wall with a window or door is removed), include the area of those existing glazed openings in your calculation.
   - For example, if an existing door/window in the wall being removed measures 4 m², this can be added to the 25% allowance.

4. Total Proposed Glazing Area:
   - Add up all proposed new glazing (windows, doors, roof lights) for the extension.
   - If the total proposed glazing exceeds the combined allowance, you will need SAP calculations.

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"A Basic SAP Calculation to Determine the Area of Glazing on Your Proposed Development
Subject to APPROVAL"

Example Calculation
- Extension Floor Area: 20 m² 
- Glazing Allowance (25%): 20 × 0.25 = 5 m² 
- Existing Glazed Openings (Removed): 3 m² 
- Total Allowance: 5 + 3 = 8 m² 

Example of a Glass Roof that needed a SAP Assessment
Property Located in Crouch End

If your total new glazing is 6 m², no SAP calculation is needed. However, if it is 9 m², you will need SAP calculations to demonstrate compliance.

Using SAP Calculations to Show Compliance
If the glazing exceeds the allowance:
1. Model the Whole Building Performance:
   - Use SAP software to compare the energy performance of the dwelling with and without the extension.
2. Compensate for Excess Heat Loss:
   - Incorporate energy-efficient measures, such as:
     - Improved insulation.
     - Better glazing (e.g., triple glazing or low U-value windows).
     - Enhanced air tightness.
     - Renewable technologies (solar panels, heat pumps).

3. Submit to Building Control:
   - Provide the SAP report, showing the extension complies with overall energy efficiency requirements.

If you would like further assistance with specific calculations or recommended software, contact our team to guide you in the right direction.

We hope you found this helpful article for your proposed loft conversion proposal, join1000s of other satisfied customers whom we have helped design to their tailored layout. Regards John. Domenech 

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07838135957

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