Skewed Free Roof Area

The "Skewed Free Roof Surface" function allows creation of skewed or non-planar roof surfaces via various options. A roof surface becomes skewed when the eaves and the ridge are no longer parallel, but both are still intended to remain horizontal and not sloped. If a roof surface is curved, for example with a wavy eave line, it can no longer be described as a skewed roof surface. In that case we refer to a non-planar (or non-flat) roof surface. Non-planar roof surfaces usually must be defined by multiple (many) points. This is then done via the function [Roof Inputs - Direct Free Roof Surface](#Roof inputs-_Direct_Free Roof su). If the roof surface can be defined by two lines, this is done via the "Skewed Free Roof Surface".

To input a skewed free roof surface, you need a normal roof surface or a [roof contour polygon](#Roof inputs-Roof contour- New R), as required for the Free Roof Surface. Both define the contour of the skewed roof surface in plan. After selecting the roof surface or the roof contour polygon, a dialog box for settings opens:

Determining the roof surface via: "2 horizontal lines" and "2 arbitrary lines". Both options largely allow the same input. The difference is that with the "2 horizontal lines" option we know that the selected lines are horizontal, so we can include a height query. For arbitrary lines this is not possible because we cannot determine at which point on a rising line the height should be measured.

Implementation: Here you enter the roof surface specification for the skewed roof surface. This also allows assigning multiple layers to the skewed roof surface. For these layers you will receive the usual quantity data in the construction data program, and you can produce "panels" with textures. Calculation of battens, laths and tiles is not possible for skewed roof surfaces.

After leaving the dialog box with 'Ok', you graphically select the two lines that will define the skewed roof surface. If you selected the "2 horizontal lines" option, you will additionally be asked for a point to determine the height position.

In both cases a dialog box opens for each line, in which you can enter a plumb or perpendicular timber offset. If the selected line lies directly within the skewed roof surface (for example an eave line or ridge line of the skewed roof surface) you do not enter an offset. Leave the fields empty and exit the dialog box with 'Ok'. If, however, you selected, for example, the front edge of a purlin, enter the desired plumb or perpendicular timber offset. For the calculation of the skewed roof surface the selected line is then automatically shifted by the entered measure.

Next you must specify the direction of the roof surface, since this is not automatically recognizable by the program for a skewed roof surface. Therefore, choose either a "line in the direction of the rafters" (e.g., verge line) or a "line perpendicular to the rafters" (e.g., eave line).

You can then specify an area in which the roof surface should be skewed. If you end the query with a right-click, the entire roof surface will automatically be created as skewed. However, if the roof surface contains ridges or valleys, it may be useful not to create the roof surface as skewed in those areas so that a normal ridge or valley rafter can still be produced. As an aid, a magenta-colored line is attached to the crosshair. This runs exactly in the direction of the rafters, as specified earlier.

Finally, specify a grid width. The skewed roof surfaces must be divided into many small roof surface segments so that a smoothly curved surface is achieved. The grid can be determined by a fixed grid width (which may leave a remainder piece at the end), a variable grid width (all fields equal width), or by the number of fields. In practice, a variable grid width between 0.5 m and 1.0 m has proven to be very effective. Care should be taken that rafters do not end up exactly on segment boundaries later, but preferably centrally within a segment.