The lima-tesa rafters give superior support to the short skirt rafters. These short purlins of variable length are supported on the pairs of Thesa files, to which they are adapted by cutting them obliquely in the appropriate way, and then nailed.
It is necessary to reinforce the union with angular plate flanges that seat in the flanks of the short rafter and the pair of file-saw, being also convenient that in the pair of file-saw the short rafters coincide with those of the slope to counteract the pushes and to be able to use the same bolts for the subjection of the angular plate flanges of both rafter.
Currently, some of these solutions are facilitated by the existence in the market of metallic elements that allow joints in a much simpler way.
In the four-way roofs, due to their construction, all the belts are permanently required by longitudinal forces, even without being subjected to horizontal wind forces.
The skirts improve the longitudinal rigidity of the roof on condition that belts and rafters are not interrupted. This circumstance must already be taken into account when making the project. Above all, care must be taken with the arrangement of the chimneys, which can cause many difficulties. For this reason, it is always necessary to ensure that the skirts are free of chimneys, these being located on the longitudinal sides of the roof, behind the main pyramids and as close to the ridge as possible.
If a large attic window is to be opened in the skirt, it should be placed in the centre.
In order to achieve good cooperation of the longitudinal and transverse bracing in the different types of roof, great importance should be attached to the most favorable position of the roofs.
The bracing can be achieved by means of tornapuntas and pendolones or by means of a horizontal envigado with intermediate belts forming a crown in form of frame and reinforcing or assuring the form of the angles of the corners.
We can say in general that for the houses that have the usual depths of 9 to 10 meters, in which we want to take advantage of the internal part of the roof as an attic or between floors will be adopted from 22o to 25o, resulting in these cases the roofs with the most economic and simple rafters.
Currently, in the case of larger spans, the situation can be resolved by placing intermediate straps that will rest on simple-shaped armour whose diagonals and uprights are joined with metal plates that replace the old nailed or glued joints.
In all the cases the structural solution will be in agreement not only to the economic aspect but also, in those cases in which it remains to the sight, the aesthetic aspect. The construction difficulties that may arise in the choice of different solutions should never be ignored. When windows are to be opened on roofs (attics), they should be opened in the smallest possible number (for aesthetic reasons). They must be adapted in form and proportions to the layout of the roof and be well distributed. In general, the shape of the windows depends on the nature of the roofing material.