Product category:
Walls
News Release from: Cavity Trays | Subject: Caviweeps and Cavivents
Edited by the Buildingtalk Editorial
Team on 03 November 2005
Control cavity wall penetrating water
and humidity
Modern building structures demand weepholes with assured functionality - so what should you look for?
When Architects and Surveyors are inspecting dpc's on sites, it is usual to check for the presence of adequate weepholes Weepholes are commonly observed above lintels, but in are generally necessary whenever there is a cavity-spanning damp course or tray
This article was originally published on Buildingtalk on 16 Jun 2003 at 8.00am (UK)
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In the past weepholes were literally open perps, left to allow water that had penetrated the external skin of a cavity wall to flow out of the structure.
Today, modern building structures demand weepholes with assured functionality.
There are many types available, but not all offer the same benefits and protection, so what should you look for when tackling that next job?.
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Weeps are now required to service water evacuation from what we term 'closed-circuit' dampcourses and cavity trays.
For instance, stopends are now fitted to lintels over window and door openings creating a defined closed circuit DPC barrier.
Arrested water cannot discharge into the cavity.
Evacuation must take place out through the structure, which might be hampered if severe wind and rain is challenging open perp exits.
Thus weepholes must be able to function proficiently at all times, despite directly blowing wind.
This can be problematic with an open perp.
Cavity Trays of Yeovil manufacture many styles of perp weep and perp vent, or caviweeps and cavivents as they are now called.
All feature protective or dyadic grille fronts that permit water evacuation despite direct wind pressure.
Interestingly, grilles also deter insects from entering the structure, an added benefit highlighted in the FMB Trade Press publication by Hilton and Oliver which states: "Do not leave the joint open so allowing rainwater to be driven in.
There are small plastic weathering devices on sale which can be inserted to give the protection required".
"There is a possibility, for example, that bees or wasps could use the cavity as a hive with the ventilation or weep holes as access points.
That is why these weep holes should be adequately protected by some device".
A Technical Standards newsletter from the NHBC makes a similar observation: "Preformed (weep) models are preferable to open perpends.
Advantageously, weeps with grilles also prevent insects from getting in.
Weeps that do not taper are less likely to block".
Cavity Trays of Yeovil manufactures caviweeps that maintain unobstructed and direct flow paths.
Such models avoid tapering or bottlenecking.
Thus blockage problems need not be an issue.
Interestingly blockage is most likely in new buildings.
In the early months when the external skin is subjected to complete saturation for the first few occasions, mortar debris washes down in the cavity.
If it cannot escape because the evacuation route exit is too restricted, problems can occur.
Thus there are three or possibly four optimum considerations when choosing a caviweep:.
* It should permit unobstructed discharge of arrested water.
* It should function despite directly blowing wind pressure.
* It should incorporate some form of insect resistance.
* Ideally, consider using a combined caviweep and cavivent.
It can be an advantage in terms of cavity wall functionality, harmonizing aesthetics and the obvious practicality of needing to purchase just one model.
Remember, open perps or open weeps cannot provide the advantages and functionality highlighted by the authoritative bodies quoted.
Look for caviweeps and cavivents with direct flow paths and a protective front.
A good caviweep will permit water to discharge even during windy conditions.
A good cavivent will permit the wall to breathe at all times, yet will protect the structure against wind-driven rain blowing across to the inside skin.
An Insect resistant front on caviweeps and cavivents is a recommended advantage.
All Cavity Trays of Yeovil products can be identified by our Company name and logo.
The Type W mentioned within this article is one of our range of caviweeps/cavivents and is the subject of European Technical Approval and LABC Product Type Approval.
Cavity Trays of Yeovil is the only cavity tray manufacturer awarded both these standards.
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