Closers Learning Curver Extract 2004
Author/Issuer: Cavity Tray Standards Added:
Extracts from The Learning Curve insert within Master Builder 2004
Closing Cavity Walls
At one time forming reveals in cavity walls was a very straightforward undertaking. One need only cut the block work of the inner skin and return it at 90 degrees to ‘close’ the cavity. A length of dpc was required to be sandwiched between the block work and the external masonry. This separated the abutting masses so dampness could not permeate inwardly. That was the theory.
The practice was different. The exercise was time consuming and subject to errors and faults. The block work return was often of a dubious standard, being irregular and poorly aligned. Cold bridging was frequently experienced and the detail suffered condensation and pickling. The roll dpc used to prevent damp transmission would tear, dislodge or simply be bridged with excess mortar. Dampness of the reveal was the accompanying legacy. Steps needed to be taken to improve the detail.
Over the years changes in the Building Regulations have prompted a rethink:
How can one minimise cold bridging around openings – the majority of traditional methods are generally now non-compliant. How can one ensure the dpc does not dislodge? To what extent can mortar bridging be reduced or even eliminated? If the structure is of a classification that requires fire integrity measures to openings, what is the easiest way to achieve this also? Finally, if the external skin is built with material of an unusual depth or perhaps is constructed against a backing block, are there any additional measures one should take to ensure the structure is built correctly to meet the latest regulation demands?
Caviclosers are the answer and can eliminate problems. There are now caviclosers of all shapes to fit perfectly the design criteria. Caviclosers are insulated and create a thermal zone to the reveal, thus cold bridging need not be a problem. Closers also act as a vertical dpc, so there is no need for conventional roll damp course to be cut and built in vertically. Closers also eliminate the need to cut and return the inside skin of block work, so construction can be more speedy. And if you require closers with fire integrity, there are now models to provide that also. But closers today are not limited to reveals only. The examples describe caviclosers for all manner of applications, whilst focusing on some specific everyday details you will undoubtedly encounter*.
*Traditional returning of the block work inner skin is still allowed if using walling materials with appropriate insulation values. In such circumstances, the Type D profiled DPC with insulation attached may be used. Being preformed in profile, unlike roll DPC, it will not distort or misplace. And it benefits an insulation layer.
TYPE V CAVICLOSER IS AVAILABLE TO SUIT A WIDE RANGE OF CAVITY WIDTHS. IT IS ALSO AVAILABLE WITH ACAVI 120 PREFIX WHICH SIGNIFIES 120 MINUTES FIRE INTEGRITY RATING
THE QUICKCLOSER INSULATOR IS WITHINA TUBE THAT CAN BE COMPRESSED TO SUIT VARIOUS CAVITY WIDTHS
CAVI 240 TYPE PWIB PARTY WALL INTEGRITY BARRIER CLOSER WITH FOUR HOURS FIRE INTEGRITY RATING
TYPE D INSULATED VERTICAL DPC CLOSER PERMITS A TRADITIONAL APPROACH WHILST BENEFITING A PREFORMED DPC SECTION
EXAMPLES COURTESY OF CAVITY TRAYS LTD FROM THE RANGE OF SIXTEEN CLOSERS
Cavities are getting wider and wider, and now there is a specific cavicloser to literally ‘fill the gap’. The Type WCA is for Wide Cavity Applications. It consists of a robust solid extrusion in which is incorporated a large insulating core. The Type WCA is available to suit any cavity width from 50mm up to 200mm maximum. One simply states the cavity width required. There are three useful lengths: 2.1metres, 3.0 metres and 3.6 metres. Stainless steel securing ties accompany all deliveries.
And if you require a closer with a fire integrity rating also, there is the Cavi 60 Type WCA. This is an up rated version with a non-combustible rock mineral wool insulation core. The Cavi 60 prefix means when tested the closer provided 60 minutes fire integrity. Maximum cavity width in this format is 150mm.
Type WCA and the fire-rated version Cavi 60 Type WCA. Ideal for wide cavities.
Cavities from 50mm to 100mm
Type V Cavicloser
One of the most economical ways of closing the typical cavity wall reveal is to use a Type V cavicloser. This lightweight easy-to-handle model has a polystyrene insulator secured within a simple jaw. Cutting to length is and fitting is rapidly accomplished, and the result is a reveal face without protrusions or projections. This permits the door or window frame to be installed in whatever position you require – subject to compliancy.
Cavities Require Closing in Many Places.
Design analysis by James Long.
In traditional construction there are requirements to incorporate fire stops within the cavity to reduce the risk of fire spreading should a structure be ablaze. The fire stops effectively close the cavity and need to be of a medium that will contain or restrict the fire for a determined amount of time.
Timber frame construction provides a straightforward example in which fire stop barriers or closers are required to isolate and compartment the cavity. They divide the structural void into individual compartments and are commonly incorporated both horizontally and vertically. In the event of fire, the flames are prevented from freely travelling via the cavity from one part of the building to another. Thus in structures of multi occupancy, every unit / accommodation benefits individual protection.
Four hour rated cavity stop/closer Cavi240 CFIS
The Cavi 240 Type CFIS is a typical example. The Cavi 240 prefix indicates 240 minutes fire integrity rating whilst the CFIS stands for Cavicheck Fire Integrity Stop. Manufactured from rock mineral wool that has a non-combustible classification, this model by Cavity Trays of Yeovil is enveloped within a polythene sleeve. Compressing and placing within the cavity secures the Cavi240 Type CFIS in position. A minimum compression of 10mm is required to adequately friction fit the integrity stop and provide a functional relationship between surfaces.
It is worth qualifying that any medium placed horizontally within a cavity should have accompanying measures to prevent penetrating water from using the top surface as a bridge to the inner leaf. There are various types of cavitray available for this purpose, including a new style launched during Interbuild week called the Type CD.
There are in excess of eight manufacturers in the UK.
Whilst the type of material used to create a fire stop varies slightly from one manufacturer to another, all are tested to the requirements of a British Standard
that is generally BS 476:Pt 20. However, not all fire stops have identical ratings, so look for the fire integrity rating duration normally indicated as minutes or hours.
Which proprietary products can one purchase that permit easy compliance?
Cavity Trays of Yeovil has launched a new up rated range of closers providing up to 240 minutes fire integrity rating. See new technical manual released by the company in April.
Timber frame construction requires barriers to isolate and compartment the cavity.
Check This Out
In a checked reveal detail the frame sits behind rather than against the external skin. Thus part of the frame face extends behind the external skin. This detail is popular in many parts of the country that experience severe weather conditions. One way of closing the cavity of a checked reveal is to use a Quickcloser. The insulation medium is contained within a tubular bag, which can be ‘squeezed’ to optimum shape to suit the cavity dimension. The tubular bag is attached to the extruded body of the closer, the front section of which is hinged.
If you are building a checked reveal, the front section is simply turned 90 degrees.
Alternatively, if you are building a straight reveal, you leave it as it is.
The Quickcloser insulating tube shapes to suit the cavity width.
Monthly Tip for Builders.
To maintain fire resistance, separating / party walls should stop about 25mm below the top of the adjacent roof trusses and appropriate fire-resistant soft packing introduced above and below the roofing underlay. This method closes the detail and provides continuity of fire integrity whilst allowing for timber roof movement.
There are Conflicting Requirements.
Party walls separating one property from another connect to the exterior skin. There is a requirement to construct in such a manner that dampness is prevented from tracking inwardly into the building and a predetermined level of fire integrity protection is also provided.
One solution is to use a party wall integrity barrier. The one illustrated is the Cavi 240Type PWIB Party Wall Integrity Barrier. (The prefix of Cavi 240 indicates it has a 240 minute (4 hour) rating). Supplied in long lengths the Cavi240 Type PWIB consists of semi-rigid profiled solid DPC to which is bonded an alkaline silicate fibre insulation layer. The profiled design ensures no mortar bridging or capillary attraction can function where the abutting party wall joins the external skin. The insulating layer is in slight compression when built in, and additionally promotes excellent acoustic restraint, addressing flanking transmission (sound attenuation).
This product was tested to BS 476: pt 20 with the maximum furnace level reaching 1136 Deg C. Cavity Trays of Yeovil supplies this product with whatever depth of bonded alkaline fibre is required to suit the specified cavity width.
FOURS HOURS FIRE INTEGRITY RATING WITH THE CAVI240 TYPE PWIB.
Closing, Closing, Closing – and a Problem.
When raising a cavity wall and constructing an opening, one is faced with a total of three ‘closing’ requirements.
The first as already covered, is the closing of the reveal brickwork using an appropriate cavicloser.
The second closing requirement occurs where the vertical closer meets the lintel. The illustration shows how the lintel is bedded down so the underside of the lintel closes tightly with the top of the vertical closer.
Finally, once the DPC or cavitray has been positioned to provide protection of whatever lintel style is used, a stopend is required to close the end to prevent collected water discharging into the cavity. And it is at this point problems can occur.
The British Standard calls for any DPC or tray to oversail the lintel by only 25mm. So where do you position the stopend?
If a lintel has only 150mm bearing and the DPC/tray overhang is 25mm, the combined total of 175mm is short of the length of a standard brick of 225mm. With no vertical perp free to receive the stopend you have to break bond.
The better practice is to have a longer DPC or tray, so you are always sure of being able to build into an ideally positioned masonry perp. Type C cavitrays for use with lintels are supplied as standard with such a greater oversail – regardless of whether the lintels have 150mm or 225mm bearings. This way you know the detail will always work and the functionality is assured.
The illustration shows how vertical caviclosers, lintel cavitrays and stopends readily unite to create a robust detail.
Questions and Answers
I supply and fit replacement windows in domestic properties. The majority of homes in my town were built prior to 1960. When the existing windows are removed, an open cavity is exposed. I fit the replacement windows in exactly the same mid-cavity position, but should I really leave the cavity as it is?
It was a common practice in the 1950’s and early 60’s for builders not to close the cavity but to rely on the window frame to cover it. Ideally you should now improve the build detail before you introduce the replacement window.
Consider use of Type O caviclosers. These are flexible insulation-filled DPC sections that can be pushed into open cavities. Their soft body adapts to the cavity width encountered.
Many replacement window companies use type O caviclosers. They find keeping some in the back of the van regularly comes in handy! It also enables them to demonstrate to the house owner that they are doing a good job by introducing a thermal and DPC enhancement. (Footnote: it is also possible to use the Quickcloser in certain existing applications if you require a rigid faceplate finish).
You refer to closing and protecting the walls, but what about the ceiling?
There is a Cavi60 Loft hatch available that is ready to screw into a trimmed opening. If is self-finished, requires no painting, and has a one hour fire integrity rating.
END OF EXTRACT