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Nailing a piece of timber

Beams, rafters and joists are the major components of a house. For a floor, the beams must both be a solid support and properly distribute operating expenses on the load-bearing walls. They can be left visible or hidden under a false ceiling. The wood species that will be used and the treatments that will eventually be administered affect the longevity of the structures.

What is the role of beams and joists?

The beams constitute the supports for joists which make up the rigid frame of the floor by resting on the load-bearing walls (or on beams). They therefore serve as a support for boards or panels made of wood (or derived from wood) and floor coverings. The framework formed by the joists may be supplemented by an insulator. beams and rafters constitute the supporting structure of the covering elements.
It is important to choose the wood essence of the beams and joists wisely. The strength and durability of this frame affect the overall strength of the house.

Which types of wood to choose for a floor by joisting?

General advice

Each species of wood has its own characteristics. For beams as for joisting, we will choose resistant, rigid and durable essences. If they must remain apparent, we will look for the aesthetic appearance of the wood, if we want to leave it in the natural state. Depending on the climate and the region, consideration will be given to the wood's ability to resist fungi and xylophagous and wood-eating insects (which feed on wood).

Wooden beams of deciduous trees

The wooden beams from hardwood trees have long been a first choice because of their high resistance. The woods poplar, ofalder, from ash or beech are used mainly for cladding and paneling, parquet flooring or furniture making. The oak, beech, chestnut are primarily dedicated to structural parts (beams and joists) but are also used for parquet.

Two flagship species for beams

  • The chestnut is a wood appreciated for its very low shrinkage (it "works" little in time). It does not sag much and is known for its smell, which is supposed to keep spiders at bay. Because of its high price, it is rarely marketed. However, it is common to find old chestnut beams, which can be useful during the renovation of an old building.
  • The Oak is the traditional woodwork par excellence. It is very resistant, but its price is high. Like the chestnut, it is often replaced by less expensive species. It has the advantage of being left raw, without particular dyeing.

Softwoods for beams

The coniferous family trees such as pine (and its various families), larch, Douglas fir and spruce grow relatively quickly and are therefore cheaper to produce. These wood species are nowadays the most used, but their relative fragility and their sensitivity to insects impose a protective treatment.

Exotic woods for beams of joist

Exotic woods (Ipe, Iroko, etc.) are little used in framing, and therefore for the manufacture of beams and joists. They are more readily available for cladding, interior and exterior joinery, and the construction of terraces and furniture.

Preventive and curative treatments for lumber

Structural lumber sold commercially stoving treatment. This is wood of class 2. If they are not exposed to moisture, they do not normally need additional treatment. Nevertheless, for safety, it is customary to apply a fungicide and insecticide treatment. It's Indispensable on reclaimed wood.
Treatments by impregnation (sprinkling, painting) or by injection may be useful to guard against the risk of invasion by xylophagous insects. It is imperative to use products with the CTB-B + label

Lumber and its standards

Because of its key role in the overall strength of the structure, the framework and wood used to build it are subject to many standards and regulations.

  • The NF P21-400 standard is relative to the strength class of the wood,
  • The DTU B52 001 stipulates rules for the use of timber,
  • The NF EN 1912 + A2 standard of June 2008 is devoted to the class of resistance as well as the assignment of visual classes and wood species,
  • The standard NF EN 14592 of March 2009 focuses on fasteners and wooden structures,
  • The standard F EN 14545 March 2009 examines the standards governing wood structures and connector elements.
It is crucial to ensure that the wood and techniques used to build a wooden floor joist meet these standards and DTU.
Environmental Protection
It is essential to verify that wood used for beams and frames comes from sustainably managed forests, protecting forest resources and their renewal. The labels PEFC and FSC constitute strong guarantees in this area.

Which wood species to choose for the beams and which treatment?: which

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