Is ventilation required and if so where does it go?

Ventilation, or to give it a fuller description; roof space ventilation, is required in some form in most circumstances. Ventilation is required to create air movement between the insulation and the underlay. This is a cold space into which air passes from inside the building. As the air passes through the insulation it cools and so loses its ability to hold as much water vapour. So if this cold, moisture-laden air is not driven outside it will form condensation in the roof space.

Ventilation grills are fitted in or near the eaves. These allow air to enter and leave the roof space through the action of the wind. If ventilation grills are also fitted at or near the ridge, fresh air is drawn in through the eaves vents and so this is much more efficient than relying on eaves vents alone.

Eaves ventilation can be in the form of over fascia1 vents or soffit2 vents. In some circumstances it could be in the form of tiles vents, spaced at regular intervals just above the eaves course.

Ridge ventilation can be in the form of a dry ridge system3 or ridge or tile vents spaced at regular intervals on or close to the ridge

1 - The fascia is the vertical board behind the gutter. The over fascia ventilator sits on top of the fascia directly underneath the eaves tiles.

2 - The soffit is a board fitted horizontally between the fascia and the wall. Ventilation grills can be incorporated into the soffit.

3 - A dry ridge system mechanically secures the ridges without the need for mortar and can ventilation into the roof space.