Rafter

The rafters or roof rafters are in roof constructions, the carrier, extending from the eaves to the ridge and carry the roof skin. In the plan, they are usually arranged at right angles to the ridge. The rafters occurs either as a single-span beam inclined, or inclined multi-span, with or without cantilever.

Word origin

The word rafter is in German since the 11th century occupied ( Middle High German " sparre ", Old High German " sparro " ), it will " lock" a common basis with the verb in the meaning " bar upright, legs spread (like the rafters on the roof) "is assumed.

Terms

The totality of the rafters of a roof is the level of the roof surfaces and is known as rafters. The concept of rafters can also appeal to the graphic representation of a rafter supervision. Today is the graphical representation of the top view of the totality of the rafters of a roof, for example as part of a detailed design, also referred to as rafter plan. The spars of a Pfettendaches be referred to as Rofen.

The truss is a matched pair of rafters, but there may be all rafters (or all wood components ) of a roof to be addressed so. The lower end of the rafter is also referred to as rafter; it extends beyond the edge of the outer wall, and is visible from the outside, is, however, to speak of a rafter head.

The bird's mouth is a triangular- shaped cut of a few centimeters in wooden rafters, so they get a bearing surface on a purlin.

Rafters with special shaping and machining are:

• Hip rafters are at the so-called Dachgraten, for example, the outer corners of a hip roof.
• Valley rafters are on the inner corners of a roof, the so-called throats.
• Schifter (or Schiftersparren ) are rafters, nestling on a ridge or valley rafters.

Depending on the installation position of the rafters they can also carry other designations: gable rafters or Ortgangsparren are at or on the gable. Flight rafters are on the outside front of the building, under the roof overhang. The attack rafters is the so-called attack point of a hip roof.

Material and task

In historic buildings were formerly exclusively rafters made ​​of solid wood for use. At the beginning of the 20th century is recommended for such wooden rafters that its free length without support should not exceed 4 meters. Today can be personalized with rafters made ​​of glulam also much greater distances bridged. Even constructions of other materials exist, and insofar rafters made ​​of steel profiles, aluminum or reinforced concrete.

The rafter has the task of initiating loads in an underlying structure. This can happen, for example over purlins in the load-bearing walls, or by means of a wooden roof truss. The DIN 1055 (load assumptions in the construction ) distinguishes between permanent loads ( the building itself ), live loads, snow loads and wind loads. The distance between the rafters with each other is specified as a center distance (s) and is in the timber usually between 50 and 100 cm, now often between 65 and 80 cm. These rafter spacings arise in solid wood statically necessary rafter dimensions between 6/12 and 10/ 20 cm. For roofs over unheated rooms today, the insulation is normally placed between the rafters. Increasing demands on the thermal insulation in recent years led in Germany to greater insulation thicknesses. Which in turn leads that when dimensioning the rafters not only static requirements play a role, but also the need to dimension according to the required insulation thickness. As such, the rafter heights are new buildings today rarely below 20 cm.

Change

Window openings in the roof surface or components that penetrate the roof, such as a chimney, make so-called replacements necessary. A horizontal upper and lower exchange exchange distribute the load in the adjacent exchange rafters. Because of the static system more substitutions in the rafter roof and the related collar roof are considered problematic. So should there dormers, ranging over more than two rafters, are avoided. A purlin roof larger substitutions are considered relatively unproblematic, and thus also the establishment of larger dormer windows.

References and footnotes

• Roof rack