Underfloor Ventilation Air Brick Calculator
Enter your floor measurements (in metres):
🔍 Why Underfloor Ventilation calculation Matters
Suspended timber floors need ventilation to prevent moisture build-up, mould, and rot. Air bricks or vents provide cross-ventilation to keep the subfloor space dry and healthy.
📏 UK Building Regulation Guidance
Approved Document C of the UK Building Regulations recommends:
1500mm² of free air space per 1m of floor wall length.
This applies to each wall that requires ventilation, and the vents should be placed at opposite sides to allow air flow across the floor void.
✅ Calculation Formula
To calculate how many vents you need:
Number of Vents = (Total Wall Length × 1500 mm²/m) / Free Area of One Vent
Where:
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Total Wall Length = Total perimeter of walls needing ventilation.
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Free Area per Vent = Typically 6000 mm² (check manufacturer specs).
🧮 Simple Ventilation Calculator
Example
For a wall length of 20m with each vent offering 6000mm² free air:
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Required ventilation: 20 × 1500 = 30,000mm²
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Vents needed: 30,000 ÷ 6000 = 5 vents
🛠️ Tips:
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Distribute vents evenly around the perimeter.
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Always place vents opposite one another to allow cross ventilation.
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Keep vents clear of blockages (e.g., soil, insulation, plants).
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Use telescopic underfloor vents for brickwork depth.
📐 Diagram Explanation
What It Shows:
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Suspended timber floor
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Cross ventilation using opposite-facing air bricks
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Arrows to show airflow under the floor void
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Correct vent placement
📋 Notes:
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Ideal for timber floors with subfloor voids
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Keeps damp and mould at bay
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Ensure vents are not obstructed
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Telescopic vents may be needed for deep cavities