Rytons A1® Fire-rated Slim Vent® Major with Flyscreen (Fire-rated Cavity Weep)

General Details

Features and Benefits:

  • Extra long perpend cavity weep hole duct, tailor-made to any length, ideal for wide externals walls such as blockwork and those with render.
  • Manufactured from A1 classified galvanised steel.
  • A pre-formed component long established as an effective method of allowing the cavity to drain freely without obstruction.
  • Replaces the vertical mortar joint for quick and easy installation and a neat, uniform appearance.
  • Front-faced galvanised steel mesh provides aesthetic screening and prevents the ingress of large insects.
  • Supplied custom powder coated to Class A2-s1, d0. Choose from the RAL Classic colour chart for a weep that blends perfectly with facing brick or mortar.
  • Suitable for:
  • The external walls of high-rise relevant buildings over 18m high (11m high in Scotland).
  • The external walls of higher-risk buildings at least 18m high or with at least 7 storeys (Building Safety Act 2022).
  • The external surfaces of residential purpose group buildings more than 11m high.
  • The external surfaces of residential purpose group buildings 11m high or less where an external wall is within 1m of the relevant boundary.
  • All other residential and non-residential buildings.

A1 Fire Classification Explained:

  • Rytons A1® Fire-rated Slim Vent® Major with Flyscreen is made from galvanised steel. Galvanised steel is considered fire class A1 without testing, as per European Commission paper 96/603/EC referred to in BS EN 13501-1:2018.
  • Classification: A1. Definition: Non-combustible. Description: No contribution to fire.


Rytons A1® Fire-rated Slim Vent® Major with Flyscreen (Fire-rated Cavity Weep)
A1 fire-rated Slim Vent® cavity weep hole duct.
Ensures the cavity of wide external walls can drain freely.
Front-faced spot welded galvanised steel flattened mesh.
Custom length x 66mm H x 10mm W (nominal size).
Custom RAL colour in matt, semi-gloss or gloss finish achieving Class A2-s1, d0.
Properties: Class A1 fire-rated 0.9mm galvanised steel. Class A1 fire-rated 06-20FG mesh. Class A2-s1, d0 fire-rated RAL colour powder coating.
Product Code: A1SVFMAJ.
Download Drawing.  |  Download Golden Thread.

Reference Material – Fire Safety:

  • England & Wales: view extracts >>
  • Approved Document B: Fire safety (Volume 1) (2019 edition incorporating 2020 and 2022 amendments) for England.
  • Approved Document B: Fire safety (Volume 2) (2006 edition incorporating 2010, 2013, 2016, 2017 and 2020 amendments) for Wales.
  • The Building Safety Act.
  • Scotland: view extracts >>
  • Building Standards Scotland Domestic Technical Handbook.
  • Northern Ireland: view extracts >>
  • Technical Booklet B (Materials and workmanship) July 2013.
  • Technical Booklet E (Fire safety) 2012.
  • Amendments Booklet – 2022 (AMD 7).

Reference Material – General:

  • NHBC Standards 6.1.17: Where fairfaced masonry is supported by lintels weep holes should be provided at a maximum of 450mm intervals and each opening should have at least two weep holes.
  • NHBC Standards 6.11.7c: Rendering shall be detailed to ensure appropriate weathertightness and durability. Issues to be taken into account include … c) weepholes. Weepholes should be provided: „„where required for ventilation to timber frame construction; „„to the last tray at stepped abutments; „„in severe or very severe exposure zones where rendering is returned back into the window or door head (weepholes are not required where the render is not returned); „to cavity trays on parapet walls.
  • The Building Regulations, Approved Document C, Internal and external walls (moisture from the ground) 5.5 (b): If the wall is an external wall, the damp-proof course should be at least 150mm above the level of the adjoining ground. 5.5 (c): If the wall is an external cavity wall provide weep holes every 900mm to assist in the transfer of moisture through the external leaf. Where the damp-proof tray does not extend the full length of the exposed wall, i.e. above an opening, stop ends and at least two weep holes should be provided.
  • British Standards BS 8215.


  • Installation is fast and easy as work proceeds with the Slim Vent® replacing a vertical mortar joint.

Rytons is proud to be a family run business and British manufacturer since 1972

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