Wet Cavity Wall Skins: Expert Guidance for Double-Damped Cavity Walls
In certain building designs, the abutment of sloping and horizontal roofs against cavity walls can lead to wet ingress, despite factors such as design and construction conforming to regulations. This issue arises because the external leaf of a cavity wall often becomes extremely wet during rainfall, and when accompanied by wind, rain saturation can occur quickly. To address this, Type X cavity trays from Cavity Trays have proven to be an effective solution for sloping abutments, being the only gable abutment tray system in the UK with European Technical Approval.
Incorporating these preformed trays helps create a damp proof course (DPC) staircase with connecting treads and risers, forming a protective barrier above the roofline. Already-attached flashings also simplify the plumber's job as they are ready-shaped and require minimal dressing.
However, a potential oversight occurs when both cavity wall skins become wet, as both are exposed externally. In a gable end parapet scenario demonstrated in the aforementioned photograph, while preformed trays offer protection against water below the roof level, the external skin can feed moisture into the building, even when the cavity remains dry.
Regulations typically rely on outward-sloping DPCs and trays discharging away from the inner masonry skin. Yet, in gable end parapet designs, where both surfaces are external and both can become wet, provisions must be made to prevent water from the wet gable skin from travelling under the slope of the tray upstand, where the two mediums meet.
Preventing ingress is accomplished through the adoption of a tray sloping upstand with a top moulded turn-down. This feature ensures the tray still functions effectively, but eliminates the possibility of saturated water under-tracking.
Cavity Trays offers an identification and scheduling service and highlights such considerations. Their approved cavity trays are accompanied by a performance undertaking intended for the architect, builder, and client's benefit. When constructing parapet wall designs, careful consideration should be given to whether the tray DPC configuration can provide an ingress route when both skins become wet. Cavity Trays, with over a century of expertise, stand ready to serve their clients' waterproofing needs.
While the turn-down lip is essential for managing water in gable end parapet designs, it should be employed in conjunction with other waterproofing measures, such as flashings and water-resistive barriers, to ensure comprehensive protection against water ingress.
In the context of home-and-garden improvements, particularly with parapet wall designs, incorporating a tray sloping upstand with a top moulded turn-down from Cavity Trays can enhance the lifestyle by providing effective waterproofing solutions, preventing damp from penetrating interior spaces. However, to achieve complete protection against water ingress in gable end parapet designs, where both cavity wall skins can become wet, it's crucial to implement this turn-down feature in combination with other waterproofing measures like flashings and water-resistive barriers.
