Invisiweep NC

Non-combustible multi-function product for discharging water from external walls. For use in any situation where water must be discharged from an external wall, e.g:

  • In external masonry walls
  • Suitable for high rise buildings above 18 metres as Regulation 7 (2) &Building Regulation approved document B
  • Suitable for high rise buildings above 11 metres as Building (Scotland) technical handbook 2019: domestic and non-domestic
  • At ground floor slab level
  • Within cavity tray systems
  • Over external lintels

Product Information


HeightWidthLengthColourPack QuantityProduct Code

  • High pressure diecast in A1 non-combustible metal protected by an electroplated coating.
  • Classified as A1, non-combustible, no contribution to fire without the need for testing according to European Commission paper 96/603/EC and BS EN 13501-1:2018
  • Integral 4mm vermin barrier and rainwater baffle as recommended to reduce ingress of large nest building insects, mammals and rainwater penetration to the cavity
  • External ribs & tapered profile, to key into mortar for secured fixing
  • Full height upstand to cavity side, to maintain drainage and minimise the impact on blockage from cavity cement build up
  • Discrete water outlet, to minimise the impact and reduce visibility for a truly concealed wall weep
  • Venturi effect outlet tube to reduce pressure, allowing for optimal water drainage

Cavity wall weeps or cavity drain units should always be installed in cavity masonry walls to allow drainage at regular intervals. They are required at ground floor, below DPC level, and must also be provided as part of any cavity tray run, including roof abutment trays, over lintels and continuous cavity tray systems, such as gas protection barrier systems.

Unfortunately, many sites are still providing a weep hole facility by simply leaving the perpend joints between bricks open, these open joints are prone to being filled.

Perpendicular joints left open can be very noticeable and result in an infestation of nest building insect and small mammals and allow the ingress of driving wind and rain, which leads to the need for a proprietary weep unit such as the InvisiweepNC. InvisiweepNC has been designed and flow tested to optimise the discharge of water while meeting the requirement for a small concealed outlet size.

  • InvisiweepNC should be used in perpendicular joints to perform the function of a drainage channel wherever water could collect inside a cavity wall such as over external lintels, or over cavity trays
  • To work effectively the InvisiweepNC should be placed directly on top of the base of a cavity tray, DPC or on the front edge of a lintel
  • Wall weeps should be placed at 450mm centres above openings with a minimum of two to comply with NHBC recommendations. Care should be taken to ensure the InvisiweepNC is kept clear of mortar and does not become blocked. This is important at the cavity side of the weep which could be blocked by mortar droppings from above
  • To calculate quantities, divide the overall length of the cavity tray, DPC or lintel by 450mm and round up to the nearest number or by 900mm if wider centres for perimeter cavity trays
  • Allow a minimum of two InvisiweepNCs per opening and one InvisiweepNC for every cavity tray stop end
  • State the product code
  • Meets British standards; BS5250, BS8000, BS5628, BS8215
  • Satisfies all NHBC requirements
  • Complies with all relevant Building Regulations
  • High pressure diecast ZL5 Zinc
  • Electroplated
  • Suitable for use in high-rise buildings with a storey 18m or more above ground level to Regulation 7(2) and Building Regulations Approved Document B.
  • Suitable for use in buildings with a storey 11m or more above ground level to Building (Scotland) technical handbook 2019: domestic and non-domestic, 2.7.

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