THE SYSTEM OF PREFABRICATION
OF WOODEN ROOF CONSTRUCTIONS

The prefabrication of wooden roof construction with nail plates has become a dominant method employed to put roofs in the USA, Australia and North and West Europe for the last thirty years. This technology was first introduced in the USA in the 1950s. In the next-ten-year period the system developed in Europe. First constructions with the plates imported from the USA, were completed in Switzerland and Norway. In 1976 the number of trusses grew, which resulted in first European factories producing nail plates- in Great Britain, Sweden and Norway.

Since the 1970s, the system has gained more and more popularity in building industry, for example, in Sweden in 1970, the production of wooden roof constructions in this technology was only 1%, in 1980- 40% and nowadays 99%. In Eastern Europe this system has been most successfully applied in Czech Republic, with the share increased to 55%.

Worth mentioning is the fact that in Denmark, where the population stands at 5 million, yearly production of trusses ranges to 350.000 (with 2000 tones of plates used).

The system of prefabrication allows for the production of various types of trusses. Although the most common are several basic types, their shape is, in fact, unlimited.

Frame trusses support not only the roof, but the whole wooden prefabricated workshops as well.

THE ADVANTAGES OF THE SYSTEM

THE APPLICATION OF PREFABRICATION
OF WOODEN ROOF CONSTRUCTION REDUCES BUILDING COSTS

  • The simple system eliminates the necessity to subcontract the roofing to other specialised firms (trusses can be obtained for home assembly, or they can be assembled by their producer).
  • Significant reductions are achieved by application of bottom chord as a construction ceiling (in constructions of both utilitarian and non-utilitarian attics), which results in elimination of expensive concrete ceiling.
  • This elimination of the ceiling (of Filigran or Teriva type) during the designing step, makes the construction lighter and results in additional savings by using lighter walls and foundations.
  • The range of assembling works on the building is reduced, which slightly speeds up the process of building.
  • There is a possibility of the roofing during the winter and, in this way, prolonging the building season.
  • The cooperation between the company and a designer during the designing step can reduce the cost of project because a constructor measures in drawings only dimensions of truss layout and load conditions. Static calculations, technical and production documentation are provided by the truss factory.
  • The investor gets familiar with the total cost of wooden roof construction during the designing step (then, in case of traditional manufacture by carpenters, we have more or less accurate estimate, and in the final calculation, the cost depends on various factors, such as: waste, skilled work, timber metalwork, impregnated wood etc).
  • As the computer program optimises the use of timber, there are substantial savings in comparison with classic constructions (20-40% less), which enables prefabrication firm to offer a lower price.
  • There is the possibility of creating great span girders (to 30min- straight elements, to 40m-arc elements), so solid wood can replace much more expensive materials, such as: steel, reinforced concrete or laminated wood.

THE PREFABRICATION SYSTEM ENHANCES THE QUALITY OF ROOF CONSTRUCTIONS

  • The fast roofing from prefabricates reduces the moisture of a building.
  • The system of production in manufacturing firm ensures high precision of manufacture.
  • Prefabricated trusses are characterised by increased capacity in comparison with trusses built in traditional methods (hammered or bolted).
  • Greater possibilities of achieving even surface simplifies coverage assembly and enables precise manufacture (the system is recommended by The Polish Association of Roofers).
  • Forming truss in tables-truss shape forms before pressing, ensures exact and strong connections as well as objective measurements.

THE SYSTEM OF PREFABRICATES MEANS GREATER SAFETY

  • The construction is based on very precise engineering calculations. They assume wide margin of safety for the capacity of timber and plates.
  • The technological process requires application of high quality timber (only suitably moist wood is used. There is no risk of common breaking of dry wall panels caused by drying of wet wood (it is reduced to about 1% for each 4% of moisture loss).
  • The program generates technological documentation, so in this way it eliminates the risk of human error while preparing the production. What is more, it reduces the risk of error made by production workers.

THE SYSTEM OF PREFABRICATION SYSTEM GIVES DESIGNERS FREEDOM OF CHOICE

  • There is a possibility of free development of attic space because trusses do not require bearing posts.
  • Roof surfaces can be freely slotted into a wall layout, especially when rebuilding already existing buildings.
  • MiTek trusses do not, in fact, require additional posts between external walls, which ensures maximum freedom of positioning internal walls. Internal foundations are not necessary then. Dividing walls can be built in light construction , and there is a possibility of their further rearranging without greater constructional changes.