Water Penetration and Retention
Water arrested by the lintel and damp course over window and door openings should not discharge into the cavity. NHBC Standards give clear and concise guidance on the use of stop ends to prevent cavity discharge and the use of weeps to evacuate the water out of the structure. Failure to address either of these requirements results in penetrating rain adversely affecting the masonry.
The accompanying picture shows what can happen in a typical cavity wall incorporating partial or full fill cavity insulation. The masonry has dried out 24 hours following rainfall, except those courses immediately rising off the lintel / dpc and around the lintel bearings. The penetrating water is unable to escape because of the absence of weeps and is retained between stopends. Damp patching is visible.
If the stopends are omitted water cascades off the ends into the cavity and into any insulating medium used within it. It then gravitates erratically moving both inwardly and outwardly affecting both skins. Internally the opening reveals become cold, damp and show tell-tale signs of pickling.
If water is retained within masonry it will initiate eventual deterioration of the structure. This can commence as a sulphate attack and occur in all masonry finishes including rendered surfaces. When freezing weather follows areas of masonry retaining water can freeze and initiate spalling.
Such problems are eliminated with the combined use of compatible Caviweeps and Type L stopends. Together these prevent cavity discharge and control water evacuation out of the structure. Available in numerous designs, sizes and colours, Caviweeps merge with the mortar or masonry style so they are hardly detectable within the exterior skin. Type L stopends are adjustable to suit a wide variety of cavity widths and dpc/ tray profiles. Both products are manufactured by Cavity Trays of Yeovil, the longest established specialist in its field.
Cavity Trays Limited Administration Centre Yeovil Somerset BA22 8HU
T: 01935 474769
F: 01935 428223