Offset Water Evacuation? A Designers Options

With common openings in external cavity walls supported by lintels of metal, concrete, stone or timber, the opportunity exists to offset the evacuation of penetrating rain so discharge is not in the vicinity of the opening.

By using preformed cavity trays with extended ends, the stopend location can be relocated away from the opening reveals and consequently, so can the weeps through which the water discharges.

Offsetting the weep location can be used for both aesthetic and structural convenience;

•  Where stone or concrete lintels are used, NHBC 6.1/05 shows the DPC stuck onto the top surface of the lintel. This is understandable if roll DPC is used, as roll DPC cannot offer preformed consistency or rigidity. In contrast, using a preformed tray permits the protection to be incorporated between window head and lintel bottom – a position that protects the entire configuration including the lintel and lintel adjacent masonry. (It also eliminates relying on sticking DPC onto the lintel top). Accordingly, preformed tray protection functions from opening level upwards, rather than from the lintel top upwards.

As water discharge cannot be through the solid lintel, and it is prudent not to position weeps immediately against lintel ends, using extended cavity trays permits water evacuation to be beyond the closing vicinity,

•  Where a ventilator or similar is adjacent to the opening reveal, extended trays often permit the protection to be common/ shared, with the weeps located accordingly.

•  Where arched openings are in close proximity, offsetting weeps can remove water volume from a confined area.

•  When a dummy timber lintel features externally, and the actual support is provided by a metal lintel with longer bearings located immediately above, offsetting the water discharge positions into masonry beyond the timber means the stain path (that commonly appears on oak where there is a repetitive flow path) does not arise.

•  Where there are a number of openings in a row, extended trays can effectively link, so subject to the extent of the masonry absorption area above, openings can share /benefit adjacent provisions and weep opportunities, and vice-versa.

Importantly, the designer should clearly specify the type of weep to be incorporated. Selection is not limited to just colour choices to harmonize with masonry or mortars. Caviweeps and Caviweep-vents (that combine weeping and ventilation) ae available with and without integral grilles and baffles. There are also Beak weeps with protected (hooded) outlets offering the designer options suitable for use in highly exposed locations. Careful selection and specification can eliminate uncertainty and chance.

Cavity Trays is the original cavity tray company, and last year celebrated 100 years of specialism. Its products are accompanied with a performance undertaking, for the benefit of architect, builder and client. The Company offers an appraisal service to industry disciplines.

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