Roof truss - what differences in structure are there?

Trusses can be constructed differently. What different types of construction exist here, and what design-related advantages and disadvantages they have, can be found in this article.

The construction of the basic roof truss types

The simplest form of the roof truss is the so-called rafter roof. It consists of two sloping roof beams, which together with the floor slab form a load-bearing triangle. The roof load is directed here directly into the outer walls, the floor slab is not loaded.

This is fitting for smaller buildings and for roof pitches of 35 to 60 degrees. However, individual rafters can - for example, for dormer - only conditionally removed or replaced, because the static causes problems.

The Kehlbalkendach on the other hand has so-called Kehlbalken that stiffen the rafters in the middle against each other. Here are larger roof structures possible.

In addition, a possible ceiling support for the attic floor extension and a so-called loft is given, both of which can often be used cheaply.

In the contact area of ​​the rafters but can often be necessary by the high shear forces concrete abutment or Rinanker, which makes the entire construction then significantly more expensive.

The third common form of roof truss is the so-called purlin roof - here the rafters rest on one or more longitudinal beams, the so-called purlins, which in turn with supports, the so-called stems, remove the load mainly on the floor slab.

Depending on the construction method, several purlins can also be used here; in the ridge area, the rafters always rest on the so-called ridge purlin.

So the most important truss forms are

  • the rafter roof
  • the Kehlbalkendach and
  • the purlin roof

The appropriate roof form is already determined by the planner or architect in advance - it must fit statically to the rest of the building construction and must not burden any part of the building too high. The occurring primary and secondary loads must therefore be accurately determined.

Tips & Tricks

In any case, leaving the roof truss up to the experienced carpenters - here, even if it looks quite simple, a lot of expertise and, above all, experience necessary.

Video Board: Mechanical Engineering: Trusses, Bridges & Other Structures (2 of 34) Ex. of Roof Trusses