Cavity Trays on water penetration and retention
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Water penetration and retention.
Cavity Trays explain the vital role of stop ends in preventing cavity discharge and the use of weeps to evacuate the water out of a structure.
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.
Type BA Cavity Barrier Arch cavitrays from Cavity Trays have been designed for use in shaped rather than horizontal cavity walls to provide opening protection. Type BA cavitrays offer total protection to the angled head, extending upwardly and outwardly to prevent the build up of concentrated water wash.
New Pyramid Weep for cavity masonry download
The new Pyramid Weep for cavity masonry from Cavity Trays replaces traditional reed straw systems. Triangular in profile, the new weep provides an aesthetically neutral means of removing water that may permeate a structure. The possible flow width of the weep is maximised due to its flat base which also allows it to bed as flat and low as possible to service water evacuation from lintels, dpc’s and trays. The Pyramid Weep is manufactured using PVCu and, as a result, will not rot.
Cavity Trays is reporting that cavity walls that support an opening using separate lintels will improve the overall thermal performance of the structural opening as the lintels do not connect and therefore do not conduct heat loss. Using this method alongside a self-supporting Cavitray and an infilling profile Cavistock enhances performances levels even further. This arrangement can promote a lintel value of up to 0.05W/mk.
Cavity Trays movement challenges the lastest British Standard PD 6697: 2010 detail that results in the entire parapet masonry above the DPC being separated from the masonry below the DPC and is not the ideal structural arrangement for a highly exposed wall at the top of a building. They outline why the use of preformed self-supporting Type P parapet cavitray is the preferred option.
Cavity Trays, already the only UK manufacturer of preformed cavitrays to hold European Technical Approval, has now secured additional approvals from LABC Registered Details (Local Authority Building Control) for preformed curved and straight cavitrays plus its extensive range of Cavicloaks.