36 BRICKS, BLOCKS & LINTELS
Steel lintels are designed to the same principles as the structural steelframe; this allows them to carry several storeys of brick and block across spans up to10m+. So like the steelframe, they need – at a minimum - to maintain their integrity for the design life of the building.
The HAPM Component Life Manual, a widely cited reference on product service life, differs on this point. It requires lintels to provide ‘35 years to first maintenance’. But should designers accept products that could potentially incur costly and disruptive maintenance, or more likely replacement, just over halfway through a 60 year building design life, the minimum for new and social housing? It’s a ‘durability risk’ that surely designers and their clients would rather design out.
Lintel durability: You do the maths
Structural engineers, Jenkins & Potter, specified Superlintels with Duragalv 140 post-galvanising as a cost-effective alternative to stainless steel for the Northampton School for Girls PFI project.
THERE ARE SEVERAL BRITISH STANDARDS RELEVANT TO LINTEL SPECIFICATION, BUT NONE GIVES A DEFINITIVE GUIDE TO CALCULATING LINTEL SERVICE LIFE. IT IS DOWN TO THE DESIGNER TO DO THE NUMBER-CRUNCHING AND DEMONSTRATE THAT LINTELS WILL PROVIDE THE REQUIRED LONGEVITY IN RELATION TO BUILDING DESIGN LIFE AND LOCATION.
Michael Miles, Director of the Lintel Specialist, Jones of Oswestry, part of Technogroup, discusses.
W
ouldn’t life be easier if lintels came with a label stating how long they will last in any given location
and application?
In fact, in an age when sustainable design demands we consider life cycle assessments of products and account for life cycle energy burden, all building products should be clearly marked with a ‘best before’ date. Construction is largely a mathematical exercise, after all, slave to dimensional
tolerances and governed by scientific principles. So why should we be any less rigorous when it comes to doing the sums and validating product life expectancy, especially for structural, load-bearing elements?
It is here - classifying the structural significance of a lintel – that we face the first major issue in assessing lintel service life. Should they be considered a ‘lifelong’ or maintainable element?
Accurate durability assessment makes a crucial contribution to the management of risk in any building project. Knowing how long products will last and what maintenance they may need helps in evaluating Whole Life Costs, including life-cycle funds for maintenance and replacement of components. It minimises the uncertainties and risks for all stakeholders in developing and operating built assets.
Worryingly, too many designers are still vague when it comes to assessing lintel durability, working under the misconception that simple compliance with standards makes a lintel fit- for-purpose.
Lintel specification, BS EN845-2:2003*, lists a number of protective coating specifications for steel lintels, but gives no clues to their relative longevity.
It acknowledges that lintel corrosion protection depends on, among other things, ‘the degree of exposure and climatic conditions’. BS 7543:2003 ‘Guide to durability of buildings and building elements, products and components’, lists in detail the factors, notably local atmospheric corrosivity, that will accelerate the weathering – and diminish the longevity - of a lintel’s protection system.
Regional corrosivity levels for the UK and corresponding zinc weathering rates are defined on the Galvanizers’ Association Zinc Millennium Map. These rates are key to evaluating if a lintel’s galvanising specification will sustain its structural integrity for the design life of the building.
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