How To Use An Over Fascia Vent | Fascia & Soffit Installation Advice (Video)
An over fascia vent is a discreet roof ventilation product fitted along the top of the fascia board to provide airflow into the roof space at the eaves. It offers a hidden alternative to vented soffits and is commonly used in new roof installations or major refurbishments.
This guide explains when over fascia vents are required, how to choose the correct size, and how to install them correctly.
What is an Over Fascia Vent?
An over fascia vent is a rigid ventilation strip fixed to the top edge of the fascia board, beneath the roof underlay. Once installed, it is hidden by the roof tiles or slates and the guttering system.
Although invisible from ground level, it provides continuous low-level ventilation at the eaves, allowing fresh air to enter the roof space.
Our fascia vents incorporate an integral insect mesh to prevent wasps, bees, and other insects from entering the roof space.
Why Should I Use an Over Fascia Vent?
Over fascia vents are typically used when:
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A clean, uninterrupted soffit appearance is preferred
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Vented soffits are not being installed
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A new roof is being constructed
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Additional eaves ventilation is required
Over fascia vents provide a practical solution where roof ventilation is needed but visible vented soffits are not desired.
10mm VS 25mm Over Fascia Vents
Over fascia vents are available in different airflow capacities:
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10mm vent provides approx. 10,000mm2 airflow per metre
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25mm vent provides approx. 25,000mm2 airflow per metre
The correct option depends on the roof pitch and the roof construction. Lower-pitched roofs and certain insulation layouts require higher airflow capacity.
UK Roof Ventilation Requirements
Adequate ventilation of the roof space is a statutory requirement in the UK and Ireland; relevant guidance includes BS 5250, Approved Document C2 (England and Wales), Technical Guidance Document F (Ireland), and Building Standards Technical Handbook Section 3.15 (Scotland).
These documents do not prescribe specific products but require sufficient equivalent continuous ventilation to control condensation risk.
In general:
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Duo pitch roofs greater than 15 degrees require 10mm equivalent continuous ventilation at the eaves
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Duo pitch roofs with slopes less than 15 degrees require 25mm equivalent ventilation
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Flat roofs with insulation at the ceiling level require 25mm of ventilation
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Duo pitch roofs with insulation following the plane of the roof typically require 25mm of ventilation
How to Install an Over Fascia Vent?
Over fascia vents are typically installed during new roof construction or during major re-roofing works, as access beneath the roofing underlay is required.
Step 1: Align the first vent section with the front edge of the fascia board. Use the integrated guiding lugs on the underside of the unit to ensure it sits flush against the fascia.
Step 2: Initial Fixing: Secure the first piece by nailing it into the top of the fascia board using screws or nails. It is recommended to place one screw or nail at each end and one in the centre of each 1mtr section.
Step 3: Interlock the Sections: Slide the male and female ends of the next section together.
Step 4: Complete the Run: Continue this process along the entire length of the fascia. At hips and valleys, the vents can be sawn to form mitred joints for a tight fit.
The video below demonstrates how an over fascia vent is positioned and fixed during roof installation, showing the relationship between the fascia, underlay, and roof covering.
