It should be noted however, the area that can be adequately ventilated by each vent can vary depending on the manufacturer and this should be confirmed prior to undertaking any calculations.īased on the above calculations a minimum of 8 vent slates are required required 4 vents should be provided on each side of the roof for cross ventilation purposes. Note: A vent capacity of 20,000 mm^2 is assumed for the purpose of this example and is a common capacity for a tile/slate vent.
(Total eaves length) x (continuous opening size) ÷ (Capacity of vent slate/tile) = (No. The assumption made above is that the form of construction will not permit conventional ventilation at eaves, thus making slate or tile ventilators necessary.
Technical Guidance Document F of the Building Regulations requires a 10mm continuous opening over the entire eaves length (or equivalent) for a roof with a pitch of 15° or more. The slated roof on the house has a total eaves length of 16m and a roof pitch of 25°.
INSTALLING RAFTER VENTS DIAGRAM HOW TO
The following example details how to calculate the number of slate/tile ventilators required to achieve the minimum required ventilation at eaves level. These can also be used at mid to high level in certain circumstances, such as in parapet walls, mono-pitched roof construction, and in mansard roofs. Used in cases where the form of the roof does not allow for conventional ventilation at eaves level. In this case, continuous abutment ventilation, as detailed in Diagram D68 should be used.ĭiagram D67c - Lean to ventilation at abutment When providing ventilation to a lean-to roof abutment, where the slope of the ceiling follows the slope of the roof in a lean-to roof, vent slates/tiles should not be used because they do not provide ventilation to the areas between all the rafters. These vent tiles/slates should always be installed in accordance with the instructions of the manufacturer.ĭiagram D67b - Ventilation at eaves using vent tile Guidelines on calculating the number of vent tiles/slates are outlined below. This type of ventilation should be used where it is not possible to ventilate the roof through the soffit, and/or at a lean-to roof abutment. If spaced openings are used, ensure they are suitably located and the total area is equal to the area of equivalent continuous ventilation. Recommended dimensions are for continuous openings. Note that the ventilators are supported by a plywood underlay. The purpose of the fly screen is to prevent insects, birds, etc. Proprietary eave ventilators should incorporates a fly screen. The diagram below shows ventilation in a pitched roof greater than 15°. The use of proprietary eave ventilators is recommended to ensure that the flow of air is not obstructed over the insulation. As previously noted if regular spaced openings are used, ensure that the openings have the same total area as the recommended continuous ventilation. The diagram above shows a dormer roof with a flat roof dormer window, the dimensions illustrated above are for continuous ventilation openings. If above a dormer window, the roof is of pitched roof construction, a 10mm continuous strip should be provided on both sides. The type of roof determines the width of the strip.ĭiagram D64 - Roof ventilation along pitch
INSTALLING RAFTER VENTS DIAGRAM FULL
This needs to be greater than a continuous ventilation strip running along the full length of the eaves. These should be adhered to avoid long-term condensation and associated problems.ĭiagram D63 - Roof ventilation - Flat roofsĬontinuous ventilation openings or some equivalent method of ventilation should have the same area on opposite. The dimensions are per Section 2.1 of Technical Guidance Document F required for continuous ventilation openings in various roof types above and below a pitch of 15 degrees. The diagram above shows the requirements for ventilation to roofs. Ventilation is essential in roof spaces to prevent harmful condensation and remove water vapour. The need for ventilation has come about due to the increase in standards of insulation combined with an increase in activities within buildings that generate water vapour.
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