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Where building standard tolerances and fire-resistant closers meet


BKE 3


BUILD ING KNOWLEDGE EX C HANG E


Consider the regularity of a typical window or door opening being constructed within a cavity wall. The tolerances permitted within the technical standards of the NHBC / LABC / Premier Guarantee allow openings to be slightly out of level, out of plumb, and out of square. The masonry type and finish can also affect the regularity and squareness of the opening - not all masonry has smooth clean square faces and edges.


Such variances can affect the fit of a fire-rated closer, which should integrate squarely and tightly between the leaves of the masonry to act as a continuous unpunctuated barrier. Uneven or incomplete (gap) integration may compromise performance in the event of a fire.


The extent by which openings in cavity walls may vary yet still be within the general tolerance limits differs pending the actual application and technical manual referenced. Examples include square reveals up to 200mm deep permitted to have plus or minus 8mm deviation off square, and reveals 6mm out of plumb increasing to 10mm out of plumb in openings more than 1.5m high.


If one considers when fire-rated closers undergo testing at an approved testing station, the disciplines and procedures are first-class, with the closers located between two non-combustible mediums. Fire is applied and the period a closer continues to act as a fire barrier is recorded. However, the question arises of whether the actual standard of build on site will match the standard of incorporation used when the product was tested? If it does not, in the event of a fire in the building, might the product perform differently?


Consider a new motor car and the normally impressive miles per gallon figure claimed by the manufacturer. In real / general use, the actual miles per gallon figure may not be as high, because the conditions applied during the testing were far more careful and accommodating than those encountered in every-day driving on the roads? Optimum build standards and every day build standards can also vary. In fact, they can be a distance apart!


There is now available a fire rated closer with a sixty minutes fire rating plus optional intumescent side strips. Known as the Cavi60 Type WCA (Wide Cavity Applications), it is designed for use in cavities up yo 150mm wide. The Cavi60 indicates the fire resistance rating in minutes.


(Our thanks to John Shillabeer, Cavity Trays Ltd, for this BKE article) CAVITY TRAYS OF YEOVIL


TEL: 01935 474769 9


WWW.CAVITYTRAYS.CO.UK


The optional intumescent strips available on the Cavi60 Type WCA expand when initiated by fire and can aid infilling of gaps. The manufacturer has pointed out the expandable strips are not a remedy for poor building standards, but are designed to improve functional incorporation in the event of being activated by fire, compared with alternatives. The integral strips have an activation temperature of 190°C and activation ratio of 8:1 @450°C.


Additionally, the Cavi60 Type WCA with Intumescent Side Strips is supplied with stainless steel ties - not plastic ties. Stainless steel ties are non- combustible and engage with the closer housing, and continue inwardly extending into the barrier insulating core itself. Ongoing core support is provided, which is not possible with plastic ties that can melt. The closer is available to suit cavities up to 150mm.


Irregular and out of plumb reveal


Beneficial products can help raise standards on site, but ultimately, the outcome will always rest with the skill of the operative and the tolerances to which that operative operates.


The Cavi60 Type WCA is available from Cavity Trays Ltd


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