• KVH’s dimensional stability is seen as helping achieve airtight structures.
• German housebuilders try to avoid treated timber.
• KVH has about half of the German construction timber market.

Interest in KVH was stirred up when TTJ first wrote about the product a year ago. So much so, that we’ve interviewed the new director of Konstruktionsvollholz (KVH), Tobias Wiegand, for more background on why it is so successful in Germany.

But first a quick reminder of what KVH is. It’s either spruce, pine, fir, larch or Douglas fir, visually or mechanically sorted and cut either with separate hearts or heart-free, with planing after drying to ensure dimensional stability. Its distinctive feature lies in the log conversion method combined with kiln drying.

The product is S10 graded (equivalent to C24) and must be dried to 15% moisture content (+/-3%) and true to size. It is available in standard lengths up to 13m due to finger-jointing, with two different finishes – Si for visible elements and Nsi for hidden elements.Dimensional stability equals +/-1mm over the cross-sectional height and width and modulus of elasticity is 11,600 N/mm².

DUO/TRIO laminated beams are a further development of KVH and consist of two or three pieces of squared timber which are glued together, with the fibres running parallel.

Housebuilder interest

Mr Wiegand said in Germany many timber members remain visible after they have been built in, with rafters and purlins popular visual architectural elements. To meet this trend, housebuilders want to buy good-looking timber members, which is made possible by the defect-cut finger-jointed KVH product. Kiln dried products’ reduced tendency for cracking and twisting adds to the visual profile of KVH.

Most German new buildings are low-energy buildings with high requirements for airtightness. In order to avoid later cracking and twisting, which could destroy part of the airtightness of the shell, once again dried timber products are needed.

“As low-energy buildings are state-of-the-art now and as the requirement for dimensional stability is also known by the housebuilders, KVH and DUO/TRIO beams are in principle the only choice for such housebuilders,” said Mr Wiegand.

“German housebuilders in general try to avoid preservative-treated timber members because of the danger of in-house emission on the one side and because of future costs at the end of the lifetime of the treated members – the costs of waste removal, for example, costs of burning in special ovens,” he added.

“As it has been shown that modern kiln-dried timber elements are not damaged by fungi or insects, then such elements are capturing the whole market.”

Mr Wiegand said safety was another argument for using KVH, as it was more strictly regulated than normal structural timber.

The KVH Monitoring Group and the Confederation of German Master Carpenters provide a clear product definition to users and regulate a uniform product specification independent of manufacturers, giving a promise of higher reliability.

Market share

Currently, KVH’s market share of the German structural timber market is 45-50%.

“We do expect that the market share will expand during the next year for the reasons outlined,” said Mr Wiegand. “Due to new legislation and standards we believe that, in the near future, almost all of the square-sawn timber will be kiln dried.”

In France and Italy, KVH sales have been greatly increased during the past few years. The product is selling in England, but quantities are still small.

Merchants’ negative perception of finger-jointing and a slightly higher price have so far limited the product take-up in the UK, even though there is evidence that finger-jointed timber is stronger than normal lumber. The product is being aimed at all types of timber application, from new build to conversions and extensions, roof additions and loft conversions, and for interior work.

German KVH producers include Ante-Holz, Gelo, Rettenmeier, Eugen Decker and Stora Enso Deutschland Gmbh. For a full list of KVH producers and more information see www.kvh.EU.