Roof Space Ventilation Requirements

3 8 7 4 ventilation of roof spaces.

Roof space ventilation requirements.

High resistance hr which has a vapour resistance greater than 0 25 mn s g or low resistance lr which has a vapour resistance less than or equal to 0 25 mn s g. Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space. Pitched roof spaces should have ventilation openings at eaves level to promote cross ventilation. Unfortunately these slates are exceptionally thin and flat and the mortar torching pointing prevents any air beneficial movement.

Additionally if the span is greater than 10m the overall ventilation area should be increased to at least 0 6 of the total roof area. Openings required by a must have a total unobstructed area of 1 300 of the. The requirements will be met by the ventilation of those roofs where the moisture from the building can pass through the insulation. To a roof space that is ventilated in accordance with 3 8 7 4.

Where the location of wall or roof framing members conflicts with the installation of upper ventilators installation more than 3 feet 914 mm below the ridge or highest point of the space shall be permitted. Duo pitch roofs greater than 20 0 pitch or greater than 10m span should have additional ventilation at the ridge to assist airflow through the roof void equivalent to at least a 3 mm wide continuous gap. Where an exhaust system covered by 3 8 7 3 discharges into a roof space the roof space must be ventilated to outdoor air through evenly distributed openings. There are normally two types of underlay used.

Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. Most building codes require a ratio of 1 150 ventilation space to attic floor space. Enter square footage calculate or enter the square footage of the attic or area to be vented. For example in the average house with a cold loft there should be a minimum of a 7mm continuous ventilation gap at eaves when using a vapour permeable underlay with a normal unsealed ceiling.

To provide adequate ventilation to a roof space you first need to be aware of the roofing felt underlay that is currently in place if at all and its type and condition. The balance of the required ventilation provided shall be located in the bottom one third of the attic space. Bs 5250 sets out the minimum requirements for roof space ventilation. Roofs with a pitch of 15 or more.

Damp in roof space as a general rule of thumb slated or tiled roofs without underslaters felt tend to breathe and ventilate through natural gaps in the slate. You can also contact your local municipality to check on building code in your area.