Non-deformable built by a pair of rafters and a transverse beam. The roof consists of a continuous series of triangular reinforcements that follow each other at the usual distances between the rafters.
As there are no belts to support the rafters, these are not only required to bending but also by axial stresses of compression and / or traction by the action of the wind, therefore their sections will be more important than in the case of roof rafters with low slope. When the length of the rafters exceeds 4.5 m, the rafters must be secured against bending, which is achieved by introducing a bridge that acts as a tension and supports the two rafters of the pair. In these cases it may also be necessary to place uprights (vertical reinforcement that is usually called right foot).
Sections are estimated.
Formerly all the joints were made of wood, today they are made of metal plates.
The loads must be transmitted to the load-bearing walls, so, in order to achieve an exact shape of the roof, these non-deformable triangles will be supported on slats that are placed on the walls in the form of straps.
In some cases it may be necessary to use longitudinal braces which are resolved with simple braces placed diagonally. The braces or diagonals of both slopes are placed crossed, so that each pair of rafters is secured at different heights.
These bracings must at the same time protect the rafters against buckling in the plane of the roof. If the struts are not attached to the side battens and are only attached to the ridge battens, the rigidity of the roof is insufficient.
In the case of very important spans or very large loads, other types of bracing may be necessary, resolved by means of a horizontal beam.
Currently, this situation can be resolved by placing intermediate straps that support on simple plywood whose diagonals and uprights are joined with metal plates.
Today all joints are solved with metal sheets.
These supports and fasteners are manufactured in standard sizes, but they are also usually joined with plates made for each particular case. These elements have solved all the problems of joints that in the past were solved by means of an elaborate carpentry work.
They are called this way or with the name of cover with skirts to that cover that presents slopes towards all the sides. They make an isolated building body stand out more and separate it from its surroundings.
In the alignments of houses close to each other, the four-way roofs rather separate, while the two-way roofs unite and give more overall effect, so that such cases, the two-way roof should be preferred.
Although skirts are usually only made on roofs for aesthetic reasons, they also have a constructive significance and importance, as they improve the longitudinal rigidity of the roof. Starting from the fact that the eaves or cornices of the roofs must protrude equally on all the fronts of the building, it is deduced that the slope must be the same on the skirts as on the longitudinal fronts. On the ground plan its edges or file appear as bisectors of the four angles that come to determine the length of the remaining ridge.
It should be borne in mind that the four-way roofs are only suitable for bodies of buildings with certain proportions in length and width, as the ridge lines too short give the building the appearance of poverty or weakness. In order to avoid these inconveniences in almost square floors it is possible to give a greater slope to the skirts than that of the main slopes of the roof.
In its construction and structure, the gable roof is much more complicated than the gable roof and requires great skill and experience to achieve a good arrangement of the lima-tesa rafters and the skirt rafters. The construction difficulties increase as the width of the work increases and are very difficult to solve when it comes to covering large premises.
When designing the roof, the first thing to fix is the position of the files or edges of the skirts. Then the position of the reinforcement is chosen taking into account a good distribution of the loads.