Roof Wizard (Automatic Roof)

This article describes how the roof wizard (automatic roof) in StatiCAD builds a complete timber, steel or light-gauge steel hip, gable or mixed roof from a roof polygon in one step. To add individual trusses and purlins, see Roof Truss Wizard and Automatic Purlins Between Trusses.

Figure 1 – Hip roof built on a three-storey reinforced concrete building (3D preview)

1. About this article

From a roof polygon and edge slopes the wizard builds the geometry of a hip, gable or mixed roof and adds the complete timber framing to the analysis model in one step: rafters, purlins, ridge beam, hip and valley rafters, verge rafters, posts, struts and fascia. The cladding load is applied as a rafter line load, or a polygon slab is meshed onto the roof surface. Openings for towers, shafts or chimneys can be cut into the roof (Section 10); a macro sets the top elevations of the walls drawn at the opening edges to the trimmer beams (Section 11).

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Which editions? The roof wizard is available in all editions of StatiCAD (like the truss and purlin wizards). The steel roof option (Section 5.1) is available in StatiCAD Ultimate and Hybrid, the light-gauge steel roof option only in StatiCAD Ultimate.

The examples use a three-storey 20 × 10 m reinforced concrete building: the beam axes of the top storey are taken as the roof polygon and a hip roof with a 33% slope is built.

2. How it works

2.1. Roof geometry

The roof polygon is the bearing line: the wall or beam axis on which the rafter feet rest. Each edge gets a slope (percent); an edge marked as gable has a vertical roof surface (the gable wall of a pitched roof). The wizard offsets the edges outwards by the eave overhang to get the eaves line and builds the roof with the weighted straight skeleton method: each edge's surface rises with its own slope, and the lines where the surfaces meet become the ridge (horizontal), hips (convex corners) and valleys (concave corners). The method gives the correct roof for non-rectangular plans as well (L, T, U and polygons with skewed edges); different edge slopes and gables can be combined.

The eave overhang is a horizontal dimension and applies to edges at the default slope; on edges with a different slope the overhang is adjusted so that the eaves stay at the same level on every face (continuous gutter line). Gable edges are extended further by the "gable overhang"; the ridge and purlins project beyond the gable wall and their ends are tied by the verge rafter.

2.2. Members

Member	Placement	Connection
Rafter	On each face perpendicular to the eaves, at the given spacing, symmetric about the middle of the face. Shortened next to hips and valleys (jack rafters).	Split at the bearing line and at purlin crossings (continuous beam). Pinned at the ridge/hip/valley end. The eave end is a cantilever.
Purlin	Contour lines: at the same levels on all faces, forming a ring that meets at hips and valleys. A purlin very close to the top of a face is omitted (the ridge beam is enough).	In the plane of the rafter axes (concentric). Pinned ends. Split at post and strut points.
Ridge / hip / valley	Skeleton lines. Collinear pieces form a single member.	Split at the bearing line, at purlin ends and at post points.
Verge rafter	Along the outer line of the gable overhang.	Rafter section.
Post	Under purlins and the ridge; bottom end at storey top level (Section 6).	Pinned bottom, continuous top; StatiCAD "truss post" type (receives no automatic support).
Strut	From each post to both sides, along the purlin/ridge it carries; at the given angle to the post.	Pinned at both ends (axial only). Shortened at the same angle if it does not fit on the post.
Fascia	Along the eaves line, ties the rafter tails.	Continuous.
Wall plate	Along the bearing line (optional, off by default).	Coincides with an RC beam if there is one on the bearing line.
Opening trimmer	Along the edge of a roof opening, in the roof plane (Section 10).	Split at the ends of the cut members, which are pinned to it. In an opening inside one roof plane it is pinned to the trimmer rafters; in other openings its corners are rigid.
Trimmer rafter	On both sides of an opening inside one roof plane, full length along the slope (Section 10.3).	Like a rafter, with the trimmer section.
Timber column (standalone roof)	Under every rafter, hip/valley and gable node on the bearing line, from the storey base (Section 4.3).	Timber Column/Post type: the base receives an automatic support, the top is continuous.

2.3. Connection to the analysis model

In the finite element model two members are not connected unless the end of one lies on the other. The wizard therefore creates every connection point explicitly:

• Edge snapping: the finite element node line of an edge beam is on its defined axis, not at the beam centre (12.5 cm outwards from the centre in the example). With "Snap edges to beam FEM lines" on (default), polygon edges are moved onto the node line of a parallel beam within 30 cm; rafter feet and hip ends are then connected to the beam.
• Splitting: rafters are split at purlin crossings, purlins and the ridge at post and strut ends, hips and valleys at purlin ends.
• Merging: ends closer than 6 cm are merged (so that beams shifted within the program's 5 cm node tolerance do not miss a connection).
• Column footprint: the program links a beam end that falls inside a column's plan footprint to the column axis with a fictitious beam. This link is made only when the beam end is within the column's elevation range; rafter, ridge and purlin ends high above a column top are not linked to the column. Rafters therefore keep their full length and regular spacing on column lines as well.

3. Opening the wizard and the roof polygon

The wizard is opened from three places: the Roof button on the left toolbar (below the Truss and Purlin buttons), Draw › Roof (automatic roof wizard)... and Macros › Roof wizard (automatic roof).... The roof is built on the active storey; the wizard does not open on the foundation level.

The roof polygon is given in one of two ways:

1. Selected polygon slab: if a polygon slab is selected in plan when the wizard opens, its corners become the roof polygon. While the window is open, the "From selected polygon slab" button can be used as well. The cladding option then switches to "Mesh the source polygon slab onto the roof" automatically.
2. Drawing in plan: the "Draw in plan" button closes the window; click the corners of the bearing line in order on the plan (Shift: orthogonal). Clicking the first point or a right click closes the polygon (at least 3 points) and the wizard opens again. Intermediate points on a straight line are merged.

Figure 2 – Roof wizard: plan preview on the left (faces, members, edge numbers), Roof tab on the right

4. Roof tab

4.1. Slope and gables

Default slope (percent; the angle in degrees is shown next to it) is the slope of new edges; "Apply to all edges (clears gables)" sets every edge to this slope and removes the gables. The edge table lists the length, slope and gable state of each edge. The slope cell can be edited; the new value is applied with Enter or when you move to another cell. Ticking the Gable box, or clicking an edge in the preview, toggles the gable (at least one edge must remain sloped). Edge numbers are shown in circles in the preview; gable edges are purple.

Figure 3 – L-shaped roof: two wing ends are gables, a valley at the inner corner; the 3D preview is rotated by dragging with the mouse

4.2. Eaves and level

Setting	Description
Eave overhang (horizontal)	Projection of the rafter tails beyond the bearing line (default 50 cm).
Gable overhang	Projection of the ridge and purlins beyond gable edges (default 30 cm).
Seated on	Top of active storey (default): the roof rests at the slab/beam level of the top storey. Base of active storey (roof storey): on a separate roof storey, the roof rests at the storey base (on the beams of the storey below); on a storey without slabs the wizard selects this itself.
Bearing line offset	Height of the rafter feet above the seating level (e.g. a knee wall).
Snap edges to beam FEM lines (≤ 30 cm)	Section 2.3.
Timber	Material of all roof members (project and library timbers).

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Separate roof storey and modal analysis: In a modal analysis with a rigid diaphragm, no node is tied to the diaphragm master of a roof storey without slabs, so the modal solution may not converge. When the roof is analysed together with the building, place it on top of the top storey (default).

4.3. Standalone roof analysis

To analyse the roof on its own, independent of a building (for example in an empty project), tick Standalone roof analysis (no building). Columns are then placed from the storey base under the nodes that would normally rest on beams: the rafter feet behind the eaves, the hip and valley corners, and the purlin and ridge nodes on gable lines (Timber Column/Post in a timber roof, steel columns in a steel roof, light-gauge steel columns in a light-gauge steel roof). They come in as columns, not truss posts, so their bases receive automatic supports. The column section is set with "Column b × h" (timber, default 12 × 12 cm) or a column profile (steel, light-gauge steel).

The posts under purlins and the ridge also go down to the storey base and become timber columns; ticking the option switches the post placement to "Equal spacing". The roof rests on top of the active storey; the seating level and beam snapping are not used (they are greyed out).

Figure 4 – Standalone roof analysis: timber columns from the storey base under the rafter feet, posts going down to the storey base; the option on the Roof tab on the right

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Number of columns and analysis: One column is placed under every rafter foot, so the column spacing equals the rafter spacing (80 columns for the 12 × 8 m example). In an empty project, the analysis of 10 × 6 m and 45 × 24 m hip roofs completed without floating-member or singular-matrix warnings; the column bases received fixed supports.

5. Members tab

Rafter spacing and section; purlins (on/off, horizontal spacing at the default slope, section); ridge beam; hip/valley rafters; verge rafter; fascia and wall plate are switched on or off individually and their sections (b × h, cm) are entered. Default sections: rafter 5 × 10 (50 cm spacing), purlin 10 × 12, ridge 12 × 16, hip/valley 10 × 16, post 10 × 10, strut 8 × 10, fascia 3 × 15.

Purlin levels are found by dividing the height of the roof's highest point evenly: the spacing is the horizontal distance at the default slope (e.g. 200 cm × 33% → a level step of at most 66 cm). The summary line shows the actual level step.

Figure 5 – Members, Posts and Load / cladding tabs

5.1. Steel and light-gauge steel roofs

When Material type on the Roof tab is set to Steel or Light-gauge steel (steel: Ultimate and Hybrid; light-gauge steel: Ultimate only), the b × h boxes on the Members, Posts and Openings tabs are replaced by a profile family and a profile per member group; the column section of a standalone roof also becomes a profile. The material list shows steel grades (default S235). Changing the type resets the material, the profiles and the layout (rafter and purlin spacing, posts, struts) to the defaults of the type; slope, polygon, eaves, openings and load settings are kept.

Type	Layout	Default profiles
Steel	Main rafters are spaced evenly along each face at up to 400 cm; the purlins (150 cm on plan) sit on the rafters; purlins, ridge and fascia sit on top of the rafters with an axis eccentricity (offset, Section 5.2). Purlins, ridge and fascia are split into spans at every main rafter and at the bearing line (Lb = span; continuous in FEM). Posts and struts are off; the cladding load goes to the purlins (Section 7).	Rafter IPE 200, purlin IPE 120, ridge IPE 160, hip/valley IPE 200, fascia UPN 120, wall plate IPE 160, post HE 100 A, strut IPE 100, column HE 160 A
Light-gauge steel	Counterpart of the timber layout: C/Σ rafters at 60 cm, purlins below the rafters, posts and struts on; the cladding load goes to the rafters. Rafter top flange screwed to cladding (restrained) is ticked by default (no lateral-torsional buckling under positive moment); untick it if the cladding is not screwed.	Rafter, purlin, ridge, wall plate CC C150x80x20x2; hip/valley CC C200x80x16x2; fascia, post, strut CC C100x60x18x2; column CC C150x80x21x2,5

Figure 5a – Steel roof (12 × 8 m hip roof, 30%): evenly spaced main rafters, purlins at 150 cm; profiles per group

Figure 5b – Light-gauge steel roof: C rafters at 60 cm, rafter top flange screwed to the cladding

Choosing "(rafter)" on the trimmer row gives the trimmer the rafter profile. The summary line shows the total weight (kg). Steel members go through the steel member check, light-gauge steel members through the light-gauge steel member check; the insufficient member highlighting and count (Section 9.3) work for both.

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Ridge of a steel gable roof: In a gable steel roof without posts the ridge beam is a load-bearing beam between the gable walls and the rafter pairs. In a 10 × 8 m example the default IPE 160 ridge (and UPN 100 purlins, if chosen) is insufficient; add posts under a long ridge or use a larger ridge profile. A 12 × 8 m hip roof with the default profiles has no insufficient member (largest ratio 0.32, IPE 200 rafter; 0.28 in the purlins).

5.2. Axis eccentricity (offset)

The Axis eccentricity (offset) options at the end of the Members tab add the eccentricity of the purlins, ridge beam and fascia relative to the rafters to the model. The finite element node stays shared with the rafter (member splitting and connections are unchanged); only the member axis is shifted with an offset (ofset2). The eccentricity is included in the analysis when "Consider Offset1 and Offset2 in the system stiffness matrix" is on in the Project Settings (the default), and the 3D view draws the member offset.

Option	Steel roof (default on)	Timber and light-gauge steel roof (default off)
Purlin	Purlins sit on top of the rafters: axis at the rafter top face + hpurlin/2	Rafters sit on the purlins: purlin axis at the rafter bottom face − hpurlin/2
Ridge	Ridge beam sits on top of the rafters	Rafters sit on the ridge beam (ridge below)
Fascia	Fascia sits on top of the rafter ends	(no option: the fascia is the board at the rafter ends)

The top and bottom faces of a sloping rafter are h_rafter/(2·cos α) from its axis vertically; the face slope is used for purlins, the default slope for the ridge and fascia. Example: IPE 200 rafter, IPE 120 purlin, 30% slope → purlin axis 10.44 + 6 = 16.44 cm above the node; 5 × 10 timber rafter, 10 × 12 purlin → 5.22 + 6 = 11.22 cm below. The options are saved with the project.

Figure 5c – Axis eccentricity options of a steel roof (members on top of the rafters)

6. Posts and struts

Posts are placed under the purlins and the ridge beam. There are two placements:

Placement	Description
Over bearing beam lines (default)	A post is placed where a purlin/ridge crosses, in plan, a beam at storey top level; its bottom end rests on the beam's node line and is connected to the beam in the analysis. For a purlin/ridge with no beam underneath, the summary shows a warning.
Equal spacing	Posts are distributed evenly without exceeding the given spacing. If there is no beam under their bottom ends they float in the analysis (a slab shell gets no interior node); the program warns.

Struts are placed from each post to both sides of the member it carries, at the given angle to the post (default 45°) and with the given horizontal length (default 60 cm). If the vertical length does not fit on the post, the strut is shortened at the same angle; a side that is too close to the neighbouring post is skipped.

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Purlin span: When posts are placed only on bearing lines, the purlin span can be as long as the beam spacing (6.5 m in the example). After the member checks, if needed, choose equal spacing and add beams under the posts, or increase the purlin section.

7. Load / cladding tab

Option	Description
As rafter line load	Each rafter receives, over a width equal to its spacing, the cladding load G (on the roof surface, kg/m²) and the snow load (on plan projection, kg/m² × cos α) as line loads (the beam's extra G and Q loads, kg/m). Defaults: G = 50, snow = 75 kg/m².
Mesh the source polygon slab onto the roof	If the roof polygon was taken from a polygon slab, the slab is fitted to the roof surface with a triangular mesh based on the beam end elevations (same as Macros › Mesh polygon slab by beam end elevations (TIN - roof cladding); see Automatically Adjusting Roof Sheathing and Post Elevations). The loads are the slab's own G/Q values; use a thin, light slab for the cladding (e.g. OSB). Nodes below the roof surface (post bottoms, struts, truss bottom chords, storey beams under the roof) are not used in the mesh; their number is reported in the summary. Roof openings inside the slab are cut out of the mesh (Section 10.2).
No load	No additional load is applied to the roof members (self-weight only).

In a steel roof the "As rafter line load" option loads the purlins: each purlin gets the cladding (on the roof surface) and snow (on plan) line loads over its spacing, the ridge beam gets the ridge strip (half a spacing on both faces) and the fascia gets the eaves strip (overhang + half a spacing). If the fascia or the ridge beam is off, that strip is added to the lowest or highest purlin; a roof without purlins loads the main rafters. In the 12 × 8 m hip example the total cladding load is 6299 kg (roof surface 122 m² × 50 kg/m² = 6108 kg; the difference is the half spacing next to the bearing line, also given to the fascia, on the safe side).

Selection group: all members are placed in a single selection group (ROOF-01, ROOF-02 …; the prefix can be changed); the group can be selected and deleted. If "Delete and replace the previous roof" is ticked, the open roof (or the previous roof on the same polygon) is deleted and the new one is built under the same name (Section 9).

8. Creating the roof and the result

"Create roof" adds the members to the model; the result window shows the group name, the number of beams and posts, the member list and warnings. An undo record is taken before and after the operation: Undo removes the roof in a single step.

Figure 6 – Example hip roof (3D preview): purlin ring, ridge, hips, posts on the beam lines and struts

9. Opening and changing a saved roof

The polygon and all settings of every roof built by the wizard are saved in the project file (V10.0.7.1 and later; .sbd and .sy4). When the project is closed and opened again, the Roof button does not open an empty wizard: settings such as rafters, purlins and posts can be changed and the same roof rebuilt.

9.1. Opening a saved roof

When the wizard opens, the roof is chosen in this order:

1. If a member of the roof is selected in plan or in the 3D view (rafter, purlin, post…), that roof is opened.
2. If a roof was built on the selected polygon slab, that roof is opened.
3. Otherwise the last roof built or opened on the active storey in this session is opened.
4. Otherwise the last saved roof of the active storey is opened; if the storey has no roof, the wizard opens empty for a new roof.

The Roof list above the preview shows all saved roofs of the project (group name and storey); choosing another roof loads its polygon and settings. — New roof — clears the polygon (the settings stay) so that a new roof can be drawn.

Figure 7 – After reopening the project the Roof button opens the saved roof CATI-01 with its polygon and settings; the button becomes "Update roof"

9.2. Updating the roof

With a saved roof open, Update roof deletes all members of the old roof and rebuilds it with the new settings under the same group name (e.g. ROOF-01); a single Undo restores it. If "Delete and replace the previous roof" is cleared, the old roof stays and a second roof (ROOF-02) is built with the new settings.

danger

Manual edits: The roof is regenerated from its settings on every update. Manual edits to roof members (moved, deleted or resized members) are lost on update; change the sections in the Members tab of the wizard.

9.3. Insufficient members

After an analysis, members of the open roof that fail the timber beam/column check in the last analysis are drawn in red in the preview (plan and 3D) and their number is shown above the preview (e.g. "Last analysis: 49 / 177 members insufficient"). The red lines are the positions of the existing members in the model; the display is switched off as soon as a setting changes, because the members move with the new settings. Without an analysis the wizard shows "Run the analysis to show insufficient members".

Figure 8 – Insufficient rafters, purlins and hip rafters of a roof with weak sections, shown in red after the analysis

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Truss and purlin wizards: The settings of the truss and purlin wizards are saved in the file as well. Macros › Edit selected truss opens a saved truss with its own settings (the window title shows the number of insufficient members in the last analysis). If the purlin wizard is opened with a purlin selected, it opens that purlin group with its settings and with the trusses it rests on ticked; Update purlins rebuilds the group under the same name.

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Roofs built with an earlier version: Roofs built before V10.0.7.1 have no settings in the file; selecting a member of such a roof and opening the wizard gives a note. To change it with the wizard, build a new roof and delete the old group.

10. Roof openings

An opening is cut into the roof for a tower, a lift or stair shaft, a chimney or a roof window. A roof can have any number of openings. They are written into the roof's record (Section 9) and applied again whenever the roof is updated.

10.1. Drawing an opening

Openings are listed on the Openings tab, the last tab of the wizard (O1, O2 …: number of corners and plan size). The roof polygon must be defined before an opening is drawn.

1. Press Draw an opening in plan; the window closes. Click the corners of the opening in order on the plan (Shift: orthogonal). Clicking the first point or a right click closes the polygon (at least 3 points).
2. The wizard opens again with the opening in the list and the members cut in the preview. The opening must be drawn on the storey of the roof; an opening drawn on another storey is not added.
3. Create roof or Update roof builds the roof with its openings.

Delete selected removes the opening selected in the list, Delete all removes all openings. An opening may extend beyond the roof edge (a tower cutting the eaves): the part outside the roof is shown with a dashed red line in the preview and gets no members.

Figure 9 – Openings tab: O1 inside one roof plane (trimmer rafters on both sides), O2 on the ridge, O3 a tower cutting the eaves; opening trimmers in magenta, the summary and the warning at the bottom

10.2. Cut members and trimmer beams

• Rafters, purlins, the ridge, hips, valleys, verge rafters, fascia and wall plates crossing an opening are cut at its edge; the cut ends are pinned. No post is placed inside an opening.
• An opening trimmer beam runs along the edge of the opening in the roof plane. The cut members end on the trimmer, which is split at those points, so they are connected in the analysis. Its section is set with Trimmer section b × h; if left empty, the rafter section is used.
• In the rafter line load mode no cladding load is applied in the opening (the rafters end at its edge). If the cladding is a polygon slab meshed onto the roof (Section 7; Macros › Mesh polygon slab by beam end elevations), the openings inside the slab polygon are cut out of the mesh: nodes are placed along the opening edge, the mesh follows the edge and no triangle or cladding load remains in the opening. At an opening crossing the slab boundary (e.g. a tower crossing the bearing line) the mesh boundary is notched along the opening edge. Only an opening that contains a corner of the slab polygon is not cut out; the result window warns about it, and for such an opening draw the slab polygon around it or use the rafter line load mode.

The summary counts what was cut, for example: "3 opening(s): 7 rafter(s) cut, 2 trimmer rafter(s); 1 purlin(s) cut, their load is carried by the opening frame; 1 ridge/hip/valley/verge line(s) cut".

10.3. Kinds of opening

Opening	Where	Load path
Opening inside one plane (roof window, small chimney)	Inside a single roof plane, at least 10 cm from its boundary.	Full-length trimmer rafters (trimmer section) run along the slope on both sides of the opening. The trimmer beams are pinned to them, and the cut rafters and purlins rest on this frame. A regular rafter closer than 10 cm to a trimmer rafter is omitted and its load goes to the trimmer rafter. The roof carries itself; no wall is needed in the opening.
General opening (tower, shaft, large chimney)	Crosses a ridge, hip, valley, verge or eaves line, or overlaps another opening along the slope.	No trimmer rafters. The trimmer beam is split where it crosses a plane boundary and each piece lies in its own roof plane; the corners are rigid. The trimmers must be carried by walls, shear walls or a frame drawn in the opening (Section 10.4); the summary warns about this.

Figure 10 – The same roof in the 3D preview: the trimmers lie in the roof planes; in the opening on the ridge (O2) the trimmer breaks at the ridge

10.4. Walls, shear walls or frames in the opening

In a general opening you draw the members that carry the trimmer beams: masonry walls, reinforced concrete shear walls or a beam–column frame. For the trimmer nodes to connect to them in the analysis:

1. Axis: draw the wall or shear wall on the opening edge; its axis in the analysis model must lie on the trimmer line. If the axis is farther from the trimmer than the finite element node tolerance (5 cm by default), the nodes do not merge. If the wall axes are known, drawing the opening on those axes is the easiest way.
2. Top elevation: the top edge of the wall must be at the trimmer elevation. A sloping trimmer means the two ends of the wall have different top elevations; instead of entering them by hand, use Macros › Match top elevations of selected walls to beam elevations (Section 11).
3. Frame: if columns carry the trimmers, place them at the corners of the opening and bring their tops to the trimmers with Macros › Match top elevations of selected posts/columns to beam elevations.

Example: when masonry walls are drawn on the edges of an opening inside one plane and of an opening on the ridge and their top elevations are set with the macro (which splits the walls crossing the ridge at the ridge), all roof nodes on the opening edges are connected to the walls in both the shell and the frame wall model, and the analysis reports no floating members.

Figure 11 – Finite element model (from the analysis): (a) opening inside one plane, wall tops follow the trimmer slope; (b) opening on the ridge, walls split at the ridge. Grey: wall shells, magenta: trimmer beams and trimmer rafters, brown: other roof members, green: opening-edge nodes connected to the walls

11. Matching wall top elevations to beams

Macros › Match top elevations of selected walls to beam elevations (right below the post/column macro) sets the top elevation of the selected walls and shear walls to the elevation of the beam running along their axis. Its main use is the walls at the edges of a roof opening: the top edge of the wall follows the sloping trimmer and the trimmer is supported by the wall in the analysis. The macro is available in all editions.

11.1. Use

1. Make the storey of the walls active and select the walls and shear walls to adjust. If none is selected, the macro asks for confirmation to process all walls on the active storey.
2. Run the macro. For each wall it looks for beams on the same storey along the wall's axis in the analysis model: parallel to the wall in plan, both ends close to the axis (within half the wall thickness, at least the node tolerance) and overlapping the wall. Trimmer beams, rafters, purlins and reinforced concrete beams all count.
3. The top elevations of the left and right ends of the wall are set to the beam elevation at those points. If several beams lie on the axis the highest one is used; among beams at the same elevation the one closest to the axis wins (the trimmer, not a rafter passing next to the opening in the same plane). The elevations are relative to the storey top, as in the wall's top elevation fields.
4. The result window lists the old and new elevations of every wall and the beams it rests on (Figure 12). Undo reverts the operation in one step.

Figure 12 – The 8 walls at the edges of O1 and O2 in the roof of Figure 9: the O1 walls (WB05–WB08) now follow the trimmers; on O2 the walls parallel to the ridge (WB09, WB11) are set to 122.5 cm, the walls crossing the ridge (WB10, WB12) are split in two at the ridge (new parts WB13, WB14) and each part follows the trimmer in its own roof plane

danger

Entering a sloping top by hand: The "left" end of a wall is the first end the program stores for it (the end with the smaller x on a horizontal wall, the end with the larger y on a vertical wall); it does not depend on the drawing direction. If the ends are swapped, the wall is built with the opposite slope and part of the trimmer nodes are not connected to it. The macro matches the ends itself.

11.2. Walls that are not changed

In the result window	Meaning	What to do
already equal	The top elevations are already at the beam elevation.	—
without a beam on the axis	No beam was found along the wall axis; the walls are listed by name at the end of the window.	Check that the wall lies on the trimmer line and that the roof is on the same storey.
would fall below the bottom level	The beam elevation is below the bottom of the wall.	Check the storey of the wall and the roof.
broken beam level along the wall	The beam has two different slopes along the wall: the opening crosses the ridge or a hip. The macro splits such a wall at the break point itself (Section 11.3); this line appears only for a wall that cannot be split because one part would be shorter than 10 cm.	Adjust the wall or the opening so that the break point does not fall at the end of the wall.
beam over part of the wall only	The beam covers only part of the wall length (e.g. 25%); the point where the beam ends is given.	Split the wall at that point and run the macro for the part under the beam.

Two notes may appear in square brackets on the line of a changed wall:

• a lower beam also lies on the axis, the highest was taken: another beam (e.g. a storey beam or a bond beam) lies on the same line below the trimmer; the wall is extended up to the highest beam.
• the beam axis is … cm from the wall FE line: the elevation was set, but the beam axis is farther from the wall axis than the node tolerance and the nodes do not merge. Move the wall or the opening onto one line.

11.3. Splitting walls at the ridge

In an opening that crosses the ridge or a hip, the trimmer passes onto two roof planes, so the elevation breaks at the ridge on the walls perpendicular to it. Because a straight top edge cannot follow two slopes, the macro splits such a wall into two walls at the break point (the ridge) and sets the top of each part to the trimmer in its own roof plane. The result window lists both parts with a "split" note and the split point (WB10 and WB12 in Figure 12).

• The split is done the same way as the program's Wall div. button (divide storey walls at intersections): the new part takes all properties of the wall (material, thickness, loads, reinforcement) and is named as the last wall of the storey. The end extensions of the parts at the split point are set to zero.
• A wall that breaks at several points (e.g. an opening crossing both the ridge and a hip) is split at each point.
• Undo reverts the splits and the elevation changes in one step.
• If the beam covers only part of the wall, the macro does not split it; it reports the point where the beam ends.

The model in Figure 11(b) was built this way: the top edges of the parts meet at the ridge.

12. Analysis notes

• For the example hip and gable roofs the analysis completed without warnings: no floating member group, no singular stiffness matrix, a normal modal analysis.
• The "Partial error occurred during the load transfer" rate may change with the roof: this is a total check in the classical load path (storey total load against the load reaching the vertical members of the ground storey). Because the posts rest on beams, the roof load is not traced in the classical path; the finite element solution is not affected.
• The note "calculation axes containing a timber joist grid but no vibration definition" comes from timber beams above the slabs of the top storey; no vibration check is required for the roof.
• Rafters, purlins and the other members are checked with the timber beam and column design; update the sections according to the results.

13. Limitations

• The settings are saved with the project (V10.0.7.1 and later). Because the roof is regenerated from its settings on every update, manual edits to its members are not kept. Roofs built with an earlier version have no settings in the file.
• Dormers, battens, collar ties (purlinless roof) and post bracing are not available yet.
• Steel and light-gauge steel roofs: no connection check (gusset, weld, bolt; screws in light-gauge steel); no roof-plane stability bracing or ties. For a light-gauge steel roof made of a truss array use the truss and purlin wizards.
• Roof openings: the cladding slab mesh (Section 7) does not cut out an opening that contains a corner of the slab polygon (draw the slab polygon around the opening). An opening edge does not snap by itself to a wall axis drawn later; draw the opening on the wall axes.
• In a standalone roof a column is placed under every rafter foot; sparser columns carrying a plate beam are not available yet.
• Curved polygon edges are not supported; if a very short edge combined with a large eave overhang makes the eaves line self-intersect, the wizard warns.