The invention relates in the first instance to a process for the construction of a dormer window, in which a rectangular piece is sawn out of the roof boarding while sawing through the purlins present there, along the two slanting boundaries of the hole formed a cheek is fixed in such a way that two essentially congruent triangles project from the roof face, between or against the cheeks a window frame is fixed, a roof section is placed on the cheeks, and the joint round the opening in the roof boarding is sealed.

Such a process is known from US Patent Specification 2,724,152. With such a process, starting from a number of parts, a dormer window can be made in a sloping roof with widely differing roof pitches. The known method is, however, relatively time-consuming: both outer and inner cheeks have to be fitted; filler strips are necessary to bridge a gap between the rebates in the side uprights of the frame and the trimming joists; the bottom side of the inner cheeks must be sawn off to prevent it from projecting underneath the trimming joists, and the outer cheeks must also be sawn to match the inner cheeks.

The object of the invention is to simplify the fitting of a dormer window, and for this purpose the process referred to in the preamble is characterized in that the bottom edge of the cheeks is provided with a trimming joist which is fixed against the sawn faces of the purlins which have been sawn through. The ends of the trimming joists will rest with their top faces against the existing roof boarding. Tiles are placed on the fitted roof section, preferably the tiles which lay originally on the sawn-out piece when the roof was still whole. In principle, two cheeks, a window frame and, if necessary, sealing strips can be supplied in one construction kit. The cheeks are, for example, triangles with angles of 110, 50 and 20 degrees. There is no need for the front-facing outside edges of the cheeks to stand vertically in the finished dormer window; consequently, the construction kit with standard parts is suitable for very differing roof pitches, for example between 30 and 50 degrees relative to the horizontal.

In order to make one single kit of parts of a dormer window suitable for various thicknesses of roof boarding, a groove is preferably provided in the top edge of the trimming joists and in the bottom edge of the cheeks, and wedge pieces are slid into opposite grooves of trimming joists and cheeks, the trimming joists are brought flush with the bottom face of the roof boarding, and the trimming joists are fixed in this position, the wedge pieces are fixed in a position in which the bottom edge thereof projects slightly beyond the tile laths, the bottom edge of the cheeks being flush with the top edge of the tile laths.

An easy, firm fixing of the trimming joists on the sawn-through purlins can be achieved if use is made of a purlin shoe.

The front edge of the cheeks will stand more or less at an angle depending on the pitch of the roof. In order to conceal this slanting position, a covering piece is fixed in front of the front edge of the two cheeks.

The seal preferably consists of an elastic, deformable plastic strip folded over the roof tiles and a strip fixed on parts of the dormer window. A suitable sealing system is described in Dutch Patent Application 161,836. This is the so-called concealed gutter system, which is universal for all types of imbricated roof covering.

The cheeks are preferably made of waterproof and weatherproof sheet material and provided with a finishing layer on the inside.

The invention also relates to a construction kit provided with at least two cheeks and a frame, a trimming joist being fitted on the bottom edge of the cheeks. The top edge of the trimming joists and the bottom edge of the cheeks are preferably provided with a groove, and the construction kit in that case has wedge pieces which can be slid into opposite grooves of trimming joists and cheeks.

The kit can also have purlin shoes for fastening the sawn-through purlins to the trimming joists, and two covering pieces to cover the front edge of the cheeks.

The invention will now be explained in greater detail with reference to the figures, in which two embodiments are shown.

• Fig. 1 shows a perspective view of the constructed dormer window, seen from the inside.
• Fig. 2 shows a perspective view of the constructed dormer window from the outside, in which the roof section of the dormer is left out.
• Fig. 3 shows a perspective view of the completed dormer window, with roof section, but without roof tiles.
• Fig. 4 shows a detail, illustrating in particular the sealing.
• Fig. 5 shows a perspective view from the inside, partially in cross section, of a variant of the dormer window according to Figs. 1 to 4.
• Fig. 6 shows a perspective view of the completed dormer window according to the variant of Fig. 5, in which a part is imagined cut away.

The first phase of the construction of a dormer window in an existing sloping roof is to saw out of the roof boarding a rectangular piece which will serve as the roof of the dormer window. This piece is indicated by 1 in the figures. Of course, this piece also has the purlin parts 2a sawn out of the purlins 2 of the roof boarding.

A cheek 3 is disposed along the two sloping boundaries of the hole formed. These cheeks are in the form of a triangle and are made of waterproof and weatherproof sheet material, with which the inside-­facing face is also finished when the construction is complete. The bottom edge of the triangles is provided with a trimming joist 4 (see Fig. 1), which is fixed against the sawn faces of the sawn-through purlins 2 and at its ends is preferably fixed against the first purlins not damaged. The top edge of the trimming joists is flush with the bottom face of the roof boarding.

A prefabricated window frame 5 is then placed between or against the cheeks 3 on the existing roof boarding and fixed in a vertical position. The front-­facing faces of the cheeks need not be vertical, which means that the cheeks are suitable for a wide range of roof pitches (for example between 30 and 50 degrees).

The sawn-out roof boarding piece 1 is placed and fixed on the cheeks 3 and the cross girder of the frame 5. For the fastening, use is made of hinges 6 with which the top edge of the piece 1 is connected to the roof boarding. It is not out of the question to use another roof section instead of the sawn-out roof boarding piece.

After laying of the roof tiles on the roof and the roof boarding piece 1, the seam round the cutout made in the roof boarding is covered with a so-called concealed gutter construction, comprising an elastic, deformable plastic strip 7 and a covering fillet 8.

Use is preferably made of the system described in Dutch Patent Specification 161,836. Drifting snow sealing elements can be added to this concealed gutter system. The strips 7 are folded over the roof tiles 9.

One advantage of the structure described is that a construction kit with two cheeks and a window frame is suitable for roofs with very differing roof pitches. The triangular cheeks with angles of, for example, 110, 50 and 20 degrees can, of course, assume a position in which the outward-facing edges 3a of the cheeks are vertical in the case of only one roof pitch. In the above-mentioned example this roof pitch is 40 degrees. In the case of other roof pitches these front edges 3a stand at an angle.

The original roof tiles 9 can be placed on the roof boarding 1, so that no additional expense need be incurred for roof covering (zinc, mastic) of the roof of the dormer window. This tile covering is also virtually maintenance-free. A neat finish is achieved by fixing the trimming joist 4 against the sawn faces of the purlins 2.

A dormer window can be constructed in a very short time by an amateur with a minimum of materials.

The embodiment according to Figs. 5 and 6 differs from that according to the preceding figures in that the connection between the trimming joists 4 and the cheeks 3 is designed in such a way that a possibility of adjustment is given. A groove is provided both in the top edge of the trimming joists 4 and in the bottom edge of the cheeks 3, and a wedge piece 11 is slid into each pair of opposite grooves.

The sequence of operations for producing the correct positioning of the various parts is as follows:

First, the trimming joists 4 are fixed against the sawn faces of the purlins 2 in such a way that the top edge of the trimming joists 4 is flush with the bottom face of the roof boarding. This flush position is achieved by itself by making the ends of the trimming joists grip the roof boarding. The fixing against the sawn faces can take place by interconnecting purlin shoes 14. A wedge piece 11 is inserted into the groove of each trimming joist to such a position that the top edge of the wedge pieces projects about 2 cm beyond the top edge of the tile lath 15. In this position the wedge pieces 11 are fixed by means of screws relative to the trimming joists 4; a cheek 3 is then placed on each of the wedge pieces, one wedge piece always projecting into a groove in the bottom face of a cheek. This bottom edge runs essentially parallel to the fixed top edge of the relevant wedge piece and is flush with the top edge of the tile laths. This position is also fixed with screws. The side walls can be finished by planks 12, it being possible to dispose a piece of foam 13 between each plank 12 and the wedge piece 11.

The shoes 14 consist of an L-shaped strip with two slanting struts.

In general, the front edge of the cheeks will be slanting, which is ugly next to the vertical frame uprights. Therefore, as shown in Fig. 6, the side uprights of the frame are provided with an external rebate in which an edge of an L-shaped covering piece 16 engages, concealing the front edge of the side wall 3 concerned.

The object of the wedge pieces 11 is to make the dormer window structure suitable for roof boarding elements with thickness differences up to about 10 cm. The object of the covering pieces 16 is to accommodate the differences in the slope of the front edge of the cheeks which are due to differences in the pitch of the roof.

Various modifications of the constructions shown are possible within the scope of the invention.