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About Roof Ventilation

In most situations, two types of passive/natural roof ventilation products are required to provide a reliable airflow and to comply with the regulations. Timloc call these ‘primary ventilators’ and ‘secondary ventilators’.

Primary ventilators are air intake ventilation components. Secondary roof ventilators maintain a clear ventilation path between the primary ventilator and where the roof felt/membrane and insulation meet.

In all cases, the primary and secondary roof ventilators must offer the required ventilation by either running continuously along the eaves or individual units spaced at regular intervals along opposite sides of the building to create a cross flow ventilation action.

Throughout this website, we will always confirm if our non-mechanical roof ventilation solutions are primary or secondary ventilators, the product’s airflow performance and the application (roof type, use and pitch) that the product has been designed for.

Product selection

Once the required level of free airflow necessary to suit the roof design has been established, the choice of ventilation components is dictated by the eaves design, method of construction, or the preference of the specifier or end user.

Timloc recommends that customers take advantage of the technical advisory service.
The Timloc Technical Services Team will be pleased to advise on the most suitable products for the application and will prepare a fully-itemised schedule of quantities if required.

Please provide as much information as possible regarding the roof design and eaves construction detail, including a dimensioned drawing (if available). Please see our Drawing Upload facility.

Upload your project drawings straight to the Timloc Technical team here: LINK.

Primary roof ventilators

Primary roof ventilators facilitate the intake of air from the atmosphere into the roof space. They are the air intake ventilation components.

These are usually housed in the soffit board or above the fascia board and comprise a slotted or meshed grille that allows air to flow freely, but prevents birds and large insects from gaining access to the roof space.

The size of the slots or mesh should be 3.5mm to 4mm in width (to meet with the requirements of BS 5250:2011), which is small enough to keep out bees and wasps but large enough to allow free, unobstructed airflow.

Primary roof ventilators fall into two categories:

• A standard pitched roof of at least 15 degrees must be provided with ventilation at least equal to a continuous 10mm opening along the eaves.
• Roof ventilation equivalent to a continuous 25mm opening is required in some other situations. These include pitched roofs below 15 degrees, flat roofs and roofs where the ceiling and insulation follow the same line at the rafters, such as dormer or mansard roof constructions.

 

Examples of primary roof ventilators are:

• Soffit vent strip  

• Over fascia vents and ventilation systems

• Push-in soffit vents

• Corbel vents

 

Common primary roof ventilation applications

• With a standard pitched roof, where the pitch of the roof is 15 degrees or greater and the roof space is an attic or loft, a free airflow is required. This must be equivalent to a continuous 10mm opening (10,000mm² per metre run). See fig.1

• With a pitched roof, where the pitch of the roof is less than 15 degrees and the roof space is an attic or a loft, a free airflow is required. This must be equivalent to a continuous 25mm opening (25,000mm² per metre run). See fig.2

• With a pitched roof where the roof space contains living accommodation and part of the ceiling and insulation follow the same line as the rafters, a free airflow is required. This must be equivalent to a continuous 25mm opening (25,000mm² per metre run). See fig.3

• With a flat roof, a free airflow is required. This must be equivalent to a continuous 25mm opening (25,000mm² per metre) see figs. 4a,4b and 4c

Can we include the line drawings of figs 1-4c in the body of text? The Bluestorm design team have these from the A4 Spec Guide page 93.

Secondary roof ventilators

Secondary ventilation components are often required.  In a typical pitched roof situation, there is always a danger that the ventilation path could be blocked at eaves level, where the roofing felt/membrane and insulation meet. 

Secondary roof ventilators fit higher up within the eaves, usually between the rafters. They hold down the roof insulation material and prevent it from restricting the flow of air to and from the primary roof ventilator to maintain a ventilation channel between the roofing felt/membrane and insulation.

As more insulation is added, the secondary roof ventilation also needs to be increased in size.

Secondary roof ventilators fall into two categories; similar to those described for primary roof vents:

• 10mm primary airflow requires 25mm secondary airflow
• 25mm primary airflow requires 25mm secondary airflow (unless close boarded, then a 50mm air channel is required)
All secondary roof ventilators are of adequate width to provide a reliable ventilation channel over insulation quilts of up to 150mm thickness (if carefully positioned and installed).

If an unusually thick insulation quilt is to be used and/or the roof pitch is quite shallow, the standard ventilators may not be wide enough. In these cases, it is recommended that two rows of secondary ventilators are installed, one above the other. Please consult Timloc Technical Services Department for further advice.

Examples of secondary roof ventilators are:

• Rafter ventilation trays   
• Roll-form eaves vents
Can we include images of the above products?

Common secondary roof ventilation applications


• With a standard pitched roof, where the pitch is 15 degrees or greater and the roof space is an attic or loft, a ventilation channel at least 25mm deep must be maintained between the roof insulation and the underside of the roof covering. See fig.1

• With a pitched roof, where the pitch is less than 15 degrees and the roof space is an attic or loft, a ventilation channel at least 25mm deep must be maintained between the roof insulation and the underside of the roof covering. See fig.2

• With a pitched roof, where the roof space contains living accommodation and part of the ceiling and insulation follow the same line as the rafters, a ventilation channel at least 50mm deep must be maintained between the roof insulation and the underside of the roof covering. See fig. 3

• With a flat roof, a ventilation channel at least 50mm deep must be maintained between the roof insulation and the underside of the roof deck. See fig.4

Can we include the line drawings of figs 1-4c in the body of text? The Bluestorm design team have these from the A4 Spec Guide page 93.

Free airflow requirements

The Building Regulations require differing levels of roof ventilation depending on the design of the roof. It is very important to identify the type of roof that is to be constructed and ensure that the correct volume of free airflow is provided by the roof ventilators.

The four main different types of roof style are:

• Standard pitched – 15° or above

• Shallow pitched – less than 15°

• Warm pitch – any roof where living accommodation is contained within the roof space

• Flat roofs

Product selection

Once the required level of free airflow necessary to suit the roof design has been established, the choice of ventilation components is dictated by the eaves design, method of construction, or the preference of the specifier or end user.

Timloc recommends that customers take advantage of our technical advisory service. Our Technical Services Team will be pleased to advise on the most suitable products to suit the application and will prepare a fully-itemised schedule of quantities if required.

Please provide as much information as possible regarding the roof design and eaves construction detail, including a dimensioned drawing (if available). Please see our Drawing Upload facility.

Upload your project drawings straight to the Timloc Technical team here: LINK

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