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Party Wall Rising Barrier – Solves Compatibility Problems

Author/Issuer: Cavity Tray Standards    Added:

Type PWRB: Party Wall Rising Barrier

What happens when two adjoining design details in the same property are incompatible?
Cavity Trays of Yeovil has come up with another simple but practical answer:

How to prevent water passing from one dwelling to another via the separating wall as depicted in the NHBC guidelines, when the usual evacuation route for such arrested water is prevented because radon / methane barriers are present in the external walls.

NHBC section 6.6 (external timber framed walls chapter) provides guidance under 6.2(d) on how a party wall should incorporate measures to prevent water that accidentally spills or floods within one dwelling from permeating an adjoining dwelling. The NHBC detail shows a drainage channel into which water can flow and discharge at the open ends of the arrangement.

Unfortunately such a shallow channel can be easily breached and/or filled with debris during the course of construction. Furthermore it is only able to accommodate a small volume of water (even if the concrete under is channelled / cast with a fall). Most importantly, if the property in question has radon or methane barriers in its external cavity walls, the inner leaf section of those barriers commonly terminate at a higher level than that of the party wall channel – so it blocks the ends of the channel. With the barrier in the way, water from the channel has nowhere to discharge.
Given that there is no alternative option for draining the water and the arrangement must maintain gas-tight integrity, merging all design requirements is problematic.

The Type PWRB Rising Party Wall Barrier provides an alternative approach. The base of the barrier acts as a dpc and extends under both skins of the party wall. The upstand acts as a dam against water flooding from within one dwelling contaminating the adjoining dwelling. The upstand is capable of holding back a far greater volume of water than a channel.
Because the profile extends upwards instead of downwards, it can oversail and interface with commonly used perimeter gas barriers. Any water can thus be directed safely into the lower portion of the perimeter wall gas barrier, from which subsequent evacuation is via the already present barrier caviweeps. At all times the gastight integrity can be maintained.
The Party Wall Rising Barrier eliminates the problem of incompatibility, increases the capacity to prevent inter-property water contamination and satisfies the design detail requirement.

2400mm x 500mm x 150mm (dimensions easily varied to suit specific site details)



Provides barrier in party wall against adjacent property water contamination
Acts as dpc at base of wall
Acts as radon & methane barrier within party wall
Provides NHBC preventative provision between dwellings
Permits interfacing with perimeter wall gas barriers
Eliminates the need to shutter and cast channel within concrete*

*This cost saving alone is often sufficient to cover the cost of the Type PWRB – so no additional money is expended on site and the work advances more swiftly. Thus there is a cost and speed advantage in addition to compatibility, greater protection, radon and methane barrier benefits, and the ability of the Type PWRB to provide the dpc element to both skins.

Showing arrangement with (optional) masonry courses present – the Type PWRB is always positioned at the base of the wall.

The upstand of the barrier extends over and into any gas perimeter cavity barrier that is present. Thus arrested water can always discharge out of the structure. In contrast, a channel outlet is substantially lower and the presence of a perimeter cavity barrier obstructs the usual channel evacuation route. Thus water is trapped and the channel floods into the adjoining property via the party wall.

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