Water Penetration at 6 o’clock  

When water penetrates the outer skin masonry adjacent to a circular opening, one of the most vulnerable points is at the base of the circular opening – the 6 o’clock position. The water will originate at higher level and track downwardly in the wall, but when it strikes a circular opening it tracks and gravitates around the outside of the curve until it reaches the lowest point – the 6 o’clock position. There is a need to adequate protect the opening head and sides, but also to make provision to manage any accumulation of water at the lowest level. A three-dimensional dpc approach is required. 

Attempts to use ordinary roll dpc usually entail it being located in the first available horizontal course above the circular opening. Such an arrangement provides head protection to arrest water permeating from higher level, but it does not protect the masonry underneath that damp course level - the masonry around the frame itself. One can build in horizontal dpc’s into courses either side, but such arrangements still provide only partial protection. Neither do they address the 6 o’clock accumulation point. If one seeks 360 degree protection, the arrangement must envelope the perimeter of the entire frame. 

The ready-made solution from Cavity Trays of Yeovil is called the Type K Cavitray. 

Manufactured from solid dpc and supplied in one piece, the Type K is ready to receive the circular window. It fits snugly around the frame establishing a 360° barrier. The entire window frame outer edge is enveloped, and is isolated from the damp masonry abutting it. More importantly, the Type K cavitray extends within the cavity outwardly and upwardly around the entire aperture. 

A physical dpc integrity barrier between both skins of masonry is established. At the bottom of the Type K an angled base projects downwardly and outwardly, to manage the dispersion of water. 

The specifier is required to stipulate the overall frame diameter plus the wall construction dimensions. If insulation is required around the opening, an accompanying Type K thermal collar can provide this. It is friction fitted onto the Type K Cavitray prior to the tray fitting onto the circular frame. Type K cavitrays are available to suit all popular sizes and a bespoke service operates for unusual and non-standard applications. 

The circular Type K Cavitray guards against damp ingress from permeating wind-driven rain. This ready-moulded solution is manufactured by Cavity Trays of Yeovil and is supplied with a performance warranty undertaking for the benefit of Architect, Builder and Client. 

One of the most vulnerable areas of any circular opening is at the bottom – the 6 o’clock position.

The concentration of water at this lowest point is dispersed via the angled base of the Cavitray.  

Details of the Type K are on page 36 of Protecting the Building Envelope, volume 22 

Cavity Trays Limited Administration Centre Yeovil Somerset BA22 8HU

T: 01935 474769

F: 01935 428223

enquiries@cavitytrays.co.uk

www.cavitytrays.com