Ensure you roof has adequate ventilation with our calculator.
Our online calculator lets tells you instantly how many vents your roof will need, including centre spacing, based on the required continuous airflow and the airflow rating of each vent.
Calculate Number of Vents
Results
Total Airflow Required: 0 mm²
Number of Vents Required: 0
Centres for Roof Vents: 0 mm apart
How to Use
- Length of Roof: simply measure your roof length in metres.
- Required Continuous Airflow: enter your Low Level (Eaves) of High Level (Ridge) airflow requirements (ususally specified by Building Control).
- Airflow per Vent: enter the mm² airflow figure specified by your chosen vents.
- Calculate: Click the 'Calculate' button to be presented with the nuber of vents required and the distance between each vent (centres).
Calculator checked on By Jamie
Calculations Used
| Airflow | Roof length × continuous airflow = total airflow |
| No. of vents | Airflow ÷ ventilation area of vent = no. vents needed |
| Centres for vents | Roof length ÷ ventilation area = vent distance |
Required Total Airflow
This depends on the length of the roof and it's specific ventilation requirements, often outlined by building control guidelines. These guidelines typically recommend a certain amount of continuous airflow, expressed in millimetres (mm), to ensure adequate ventilation and prevent moisture buildup in the roof space.
Example: If a 10 metre long roof requires 5mm of continuous airflow, the total airflow required would be:
Total Airflow = 10,000 mm (roof length) × 5 mm (continuous airflow) = 50,000 mm²
Number of Vents
Each vent has a specific airflow capacity measured in square millimetres (mm²). By dividing the total airflow by the airflow capacity of a single vent, you can determine the number of vents required.
Example: if your total airflow requirement is 50,000 mm² and each vent provides 20,000 mm² of airflow, the calculation would be:
Number of Vents = 50,000 mm2 (total airflow) ÷ 20,000 mm² (airflow per vent) = 2.5
Note: Since it's not practical to install half a vent, you would round up to the nearest whole number, meaning 3 vents would be required in this scenario.
Centres for Vents
Proper spacing ensures that the vents are evenly distributed along the length of the roof, allowing for optimal airflow. To find the centres for the vents, divide the length of the roof (in millimetres) by the number of vents.
Example: if your roof is 10,000mm long and requires 3 vents, the calculation would be:
Vent Centres = 10,000 mm (roof length) ÷ 3 (number of vents) ≈ 3,333 mm apart
Frequently Asked Questions
Why is roof ventilation important?
Proper roof ventilation helps regulate temperature and moisture levels in your attic or roof space, preventing damage to roofing materials, reducing energy costs, and prolonging the lifespan of your roof.
Without adequate ventilation, you might experience issues like mould growth, wood rot, or increased energy bills due to overheating.
How do I know if my roof needs more ventilation?
Signs include excessive heat buildup in the attic, noticeable mould or mildew, rusting nails, or warped wood. If you see ice dams forming on your roof in winter or your energy bills are unusually high, your roof may need additional ventilation.
What types of roof vents are there?
Popular vents include ridge vents, soffit vents, gable vents, and turbine vents. Each type serves a specific purpose and is installed in different areas of the roof to ensure balanced airflow. For instance ridge and soffit vents are commonly used together to create a continuous flow of air through the attic space.
Can I install the vents myself?
While you may feel comfortable installing vents, it's generally recommended to hire a professional roofer to ensure proper, safe installation.
What happens if I install too many?
Installing too many vents can actually disrupt the balance of airflow, leading to inefficient ventilation.
How do I maintain my vents?
Roof vents require minimal maintenance, but it's a good idea to inspect them annually. Ensure they are not blocked by debris, such as leaves or bird nests, and check that the vent screens are intact to prevent pests from entering your attic.
What if my roof has an unusual shape?
For roofs with unusual shapes or multiple levels, ventilation needs may vary. In this instance we recommend you consult a roofing professional who can assess your specific roof design and recommend the appropriate ventilation strategy.
Can poor ventilation cause roof leaks?
Poor ventilation itself doesn’t directly cause leaks, but it can contribute to conditions that lead to leaks, such as condensation buildup and ice dams.