Round small - diameter timber for construction Final report of project FAIR CT 95 - 0091

The use of small-diameter timber in construction has been investigated. The aim of the work is to increase the use of the wood harvested in forest thinning in construction applications. The work has covered a wide range of aspects, from availability of the material to design of the structures. This publication summarizes the results in following areas: availability, dimensions and quality of conifers harvested in forest thinning, cost of harvesting and woodworking, comparison of drying methods: seasoning, warm-temperature and hightemperature kiln-drying, improving durability, strength of round small-diameter conifers, potential types of structures to be built from round timber and new mechanical joints. The tree species that were included in the study are Scots pine, Norway spruce, Sitka spruce, Larch and Douglas fir. The main reasons why round timber is rarely used in construction can be summarized as: the material is not available via the normal commercial routes, the roundness requires special methods and systems that are not known by architects and carpenters, the strength values of timber connections are not available for engineers, the lack of standards and models. This research aims to produce information needed in the use of small roundwood in load-bearing structures in order to remove the obstacles mentioned above. Results concerning availability of construction-quality round timber in the first commercial thinning reveal that the resource itself is vast: millions of cubic meters in Finland alone. The yield per hectare is, however, limited and dependent on the dimensions required. When the diameter of the final product is