Demanding timber structures require demanding products

Wood has already been used for centuries as a building material.  Where the knowledge and expertise of the master builder determined the use of wooden components in the past and consequently insured tradition for wooden construction, today the use of our products is decided according to site safety, customary uses and type of use.  In addition to the structural requirements, such functions like acoustic insulation, fire protection and thermal protection must be met in particular.  But also aesthetics and ecology play an important role.  The properties required can be found in various standards and agreements.

Technical bases and the most important standards

Agreement concerning KVH, agreement concerning Duo/Trio beams
KVH® monitoring association and the German Carpenters Association, 2003-11

DIN 4074-1 Sorting of wood according to bearing capacity DIN 1052-1/A1 Timber structure.  Calculation and design, 2004-08 DIN 68140-1 Finger-jointing for wood, 1998-2 DIN 68800 Wood protection, T2: Preventive structural measures, T3 Preventive chemical wood protection, 1990-4 DIN 18334/VOB/ATV Awarding and contractual rules for building services - Part C: General technical conditions of contract for building services (ATV) 2005-01 DIN EN 388 Structural wood for bearing purposes, strength classes, 2003-09

A full listing appears under Technical Information.

Supporting wooden components must be structurally measured in accordance with DIN 1052. The material characteristics indicated here, such as elasticity module, permitted stresses apply exclusively to coniferous wood, which has been sorted in accordance with DIN 4074-1. This governs the criteria that coniferous wood must meet for the wood to be structurally measured.  These characteristics are:

Wane, knots, width of annual rings, slope of grain, cracking, discolouration, insect attack, etc.

On visual sorting, DIN 4074-1 distinguishes the following classes:

S 7       Sawn wood with low bearing capacity

S 10      Sawn wood with customary bearing capacity

S 13     Sawn wood with above average bearing capacity

The structural timber products in the Rettenmeier Zunftholz^® range are sorted as S 10 TS. TS stands for sorting in dry state.

In addition to the characteristics in question, there are "increased requirements" for sawn wood products that must be included in agreements. For example, therefore, blue stain is not permitted for visible application of KVH and QLH, contrary to DIN 4074-1.

Important features of wood appearance are visible cracks. Although these in most cases (dry cracks) have no effect on the structural bearing capacity, they are often the subject of complaints. Planners and owners use visible wood components as a design element. They consequently regard major cracks as an optical defect. Apart from technical drying, the cutting method, above all, is of decisive importance in reducing anticipated dry cracking. A cut at least free of heart center, is common practice today. Increased requirements over DIN 4074-1 apply to visible qualities in agreements for KVH and QLH.

The sorting features for KVH and QLH are shown in tabular form in Technical Information.

DIN 68800-2 allows us to do without chemical wood protection, especially in home building. To achieve this, the individual components must be graded in hazard class GK 0.

Research into building damage claimed has shown that excessive wood humidity is responsible for much of the damage complained about. In principle, therefore

          o use construction wood dry and keep it dry;
          o prevent insect attack, or keep it under control.

For structural wood protection, dried timber must also be protected against dampness in transit and when stored on site.

The selection of wood also gives planners the opportunity for special wood protection. So-called coloured heart timbers (e.g. Douglas fir) display higher resistance to fungal attack and are therefore often used for thresholds in an outside wall. If it is certain that no greater humidity stress will occur at the other wall surfaces then GK 0 can be used as a base and chemical wood protection can be omitted.

Even lath and formwork can be used without chemical wood protection if the cavity between the outer skin of the component and the roof covering is ventilated. Encroaching humidity can then be removed and potential fungal attack excluded. Because of the relatively small cross-section, insect attack is unlikely.

If the prerequisites for dispensing with chemical wood protection exist, this should be done on health and ecological grounds as well.

Unstressed timber construction ensures a healthy residential climate and ensures further material or thermal use after structural use.