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Sticking to the facts

Letters

If urea formaldehyde really was the glue in the joints of the failed Bad Reichenhall timber roof girders (NCE last week), it is not surprising that the tragic collapse occurred.

Building esearch Establishment Information Paper 19/82 dated September 1982, written by IS McIntyre and DP Birch, considered the design of timber flat roofs.

Extracts from the paper are: 'Chipboard bonded with urea formaldehyde suffers a significant, and irreversible, loss of strength on wetting and cannot be recommended for decking in flat roofs. Melamine/ urea or phenol bonded chipboard loses less strength on wetting and redrying;

Plywood incorporating a WBP adhesive?can tolerate occasional wetting without incurring a significant permanent loss in strength.' 'Similar considerations apply to the structural members of wood-based flat roofs which can consist of timber joists or laminated beams, or built-up members in which sheet materials are combined with solid wood using glue, nails or other fasteners.

The performance of these structural members is a critical consideration, taking into account the implications of failure and thus there is merit in employing a sufficiently durable species and if relevant, a glue of the WBP type.' It seems that for over 20 years urea formaldehyde has not been recommended for timber structures subject to damp conditions.

John E Acton (M), The Jays, 1B New Street, Charfield, Wotton-under-Edge, Gloucestershire, GL12 8ES

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