It can be hard to keep up with all the standards for building products, especially as they frequently change. In this column, Barry Hunt throws some light on the standards, identifying those you need and those you don’t. This time he looks at BS 5642, Sills and Copings.

This is now the oldest standard still currently used. It deals with natural stone materials for use in construction. Strange, then, that it seems to have been forgotten about and is rarely cited.

It is split into two parts, Part 1 for window sills (or cills) and Part 2 for copings.

This standard has not been altered in 30 years. Why would it have been? It is relatively simple and straightforward, primarily dealing with quality and tolerances. There are many cross references, mostly now out of date. The current replacement standards it refers to do not provide much additional advice or information.

The two parts of BS 5642 both concentrate on the form of the sills and copings, and not the materials used to create them. Therefore the sections dealing with slate and natural stone are relatively short. So, as far as the stone elements are concerned, for your £48 for each part of the standard you get about a page of text. Comparing the two parts, much of the text is the same, so there is not a lot for your £96. Especially as the suggested testing regime for slate is essentially defunct.

The diagrams provided for sills are well drawn and easily understandable but are not up to speed with current developments. This is not really an issue as it should be possible to fit the basic principles for sills into any current design.

There are diagrams for sills to be used with metal windows, something that is essentially now outlawed by the current building regulations because of cold-bridging issues.

Ultimately, the advice for sills should be to have sufficient overhang with a drip line, a slope and a shelf to site the window upon.

Only a couple of diagrams are provided for copings, which are very simplistic and concentrate on the most important aspect – that is: the incorporation of a substantial drip line.

It must not be forgotten that sills and copings are dimensioned stone and thus ought to conform to the requirements of BS EN 12059, except where they have curved profiles. Unfortunately, BS EN 12059 does not provide much additional guidance and simply requires a range of test results to be declared.

Sills and copings have to provide a level of defence to weathering mechanisms and any future revisions should seek to determine a minimum level of performance in the recommended tests.

On the arbitrary value for money scale I have devised, I rate BS 5642 at 15%, mostly because it has now lost the majority of its relevance. It should be scrapped, but there is presently nothing to take its place.

Ideally, a new standard should be devised dealing with natural stone elements in the built environment, although it does not seem likely that this will actually happen with the way standards are presently being compiled.

Therefore it may be better for the Stone Federation to publish the necessary guidance, taking into account the extensive changes to the building regulations that have occurred over the years.

Fall, overhang and drip. This is all you need to think about regarding the shape of a sill or coping, so how do we always manage to over-complicate matters.

Just make sure the stone itself is up to the task, and for this there is nothing like going and viewing some long established examples.

References:

BS 5642-1:1978. Sills and copings. Part 1. Specification for window sills of precast concrete, cast stone, clayware, slate and natural stone. Published by the British Standards Institution (BSI), London, England.

BS 5642-2:1983. Sills and copings. Part 2. Specification for copings of precast concrete, cast stone, clayware, slate and natural stone. Published by the BSI, London, England.

BS EN 12059: 2008+A1:2011. Natural stone products – Dimensional stone work – Requirements. Published by the BSI, London, England.

Barry Hunt is a Chartered Geologist and Chartered Surveyor who has spent 20 years investigating issues relating to natural stone and other construction materials. He now runs IBIS, an independent geomaterials consultancy undertaking commissions worldwide to provide consultancy, inspection and testing advice. Tel: 020 8518 8646.

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