The Roof tool in ARCHLine.XP is used to create and edit parametric roof geometry, from simple flat or pitched roofs to complex multi-plane and custom-shaped roof structures.

A roof is part of the BIM model. Its geometry, materials, layers and structural components can be edited throughout the design process, while the resulting changes are reflected in the related architectural views and documentation.

ARCHLine.XP provides three main methods for creating roofs:

1. Roof by Footprint
2. Roof by Plane
3. Roof by Extrusion

The appropriate method depends mainly on the geometry of the roof and on the information available when the roof is created.

Understanding the roof model

Before creating a roof, it is useful to distinguish between three different aspects of the roof:

Roof geometry

The roof geometry defines the overall architectural form of the roof:

• footprint,
• roof planes,
• slopes,
• ridges,
• hips,
• valleys,
• gable ends,
• eaves and overhangs.

Roof build-up

The roof can have a layered construction representing the physical build-up of the building element.

Typical layers may represent:

• roof covering,
• battens,
• thermal insulation,
• structural layers,
• internal finishes.

The layer structure can be used in sections and other architectural documentation.

Roof structure

The supporting timber or structural system can be modeled in addition to the architectural roof.

Typical roof structure components include:

• rafters,
• eaves purlins,
• intermediate purlins,
• ridge boards,
• collar beams,
• battens.

Keeping these concepts separate makes complex roof models easier to understand and edit.

1. Roof by Footprint

Roof by Footprint is the most commonly used method for creating conventional architectural roofs.

The roof is generated from a closed boundary representing its footprint.

There are two main ways to define this boundary:

• Sketch the footprint
• Pick walls

Sketch the footprint

Use this method when you want to define the roof boundary manually.

Draw a closed contour representing the roof footprint and specify which boundary edges define sloping roof planes.

This method can be used to create many common roof forms, including:

• flat roofs,
• shed roofs,
• gable roofs,
• hip roofs,
• pyramidal roofs,
• gambrel roofs,
• mansard roofs,
• combinations of these forms.

Pick walls

Use Pick walls when the external walls of the building already define the basic shape of the roof.

Select the walls forming the closed building perimeter.

ARCHLine.XP generates the roof boundary and calculates the intersections between the resulting roof planes automatically.

This is particularly useful when creating a conventional pitched roof directly above an existing building model.

Roof boundary and roof planes

The footprint does more than define the external contour of the roof.

Each boundary segment can determine how the corresponding part of the roof behaves.

A boundary can create a sloping roof plane, or it can form a gable end.

This makes it possible to create different roof configurations from the same footprint.

For example, a rectangular footprint can be used to create either a hip roof or a gable roof simply by changing the behavior of selected boundary edges.

Roof slope

The inclination of the roof planes is controlled by the roof slope.

Different edges of the same roof can have different slope values.

This allows the creation of asymmetric and more complex roof forms.

Changing the slope automatically modifies the corresponding roof geometry and may change the position of ridges, hips and valleys.

When designing the roof, it is useful to check the result simultaneously in:

• Floor Plan,
• Elevation,
• Section,
• 3D View.

Gable ends

A footprint edge does not necessarily have to generate a sloping roof plane.

By disabling the slope for a selected boundary, that side becomes a gable end.

For example, starting from a four-sided hip roof, disabling the slope on two opposite edges creates a typical gable roof.

This makes it possible to switch easily between different roof configurations without recreating the complete roof.

Roof overhang

The overhang defines how far the roof extends beyond its reference boundary.

Overhangs can be modified during the design process.

This allows the roof geometry to respond to architectural requirements such as:

• protection of the façade,
• covered terraces,
• traditional large eaves,
• gutters and drainage,
• shading.

Different roof edges may require different overhang conditions.

Recommended illustration:
Wall line, roof reference line and roof overhang shown in section.

Custom roof profiles

A roof plane does not always have to use a simple straight cross-section.

For special architectural forms, a custom profile can be used to define the roof geometry.

This makes it possible to create roofs with more complex cross-sections and architectural character.

Custom profiles are particularly useful for historic, traditional or specially shaped roofs where conventional planar geometry is insufficient.

2. Roof by Plane

Roof by Plane creates an individual roof plane instead of generating the complete roof from a footprint.

This method provides more direct control over the geometry and is particularly useful for:

• irregular roofs,
• extensions,
• existing buildings,
• surveyed roofs,
• complex roof combinations,
• individual roof surfaces.

Individual roof planes can be combined to form a complete roof.

There are two principal methods for defining the inclination of the plane.

Roof plane by reference line

A roof plane can be defined using a reference line and an inclination.

The reference line determines the orientation and reference position of the roof plane.

The slope determines its inclination.

This method is useful when the architectural geometry and required roof pitch are already known.

Roof plane by three points – P3

The P3 method defines the roof plane using three points with known elevations.

Three non-collinear points uniquely determine the position of a plane in 3D space.

This method is especially useful when reconstructing an existing building.

For example, if three points of an existing roof have been measured, ARCHLine.XP can generate the corresponding roof plane without requiring the original roof slope to be known.

3. Roof by Extrusion

Roof by Extrusion is intended for roof forms whose geometry is better described by a cross-sectional profile than by individual planar roof surfaces.

A profile is defined and then extruded along a direction to generate the roof.

The profile can be:

• a predefined parametric shape,
• or a custom sketched profile.

This method is suitable for forms such as:

• barrel roofs,
• curved roofs,
• arched roofs,
• special industrial roofs,
• profile-based architectural roof forms.

Editing the roof

A roof remains editable after it has been created.

Depending on the roof type, you can modify characteristics such as:

• footprint,
• boundary edges,
• roof slope,
• overhang,
• elevation,
• individual roof planes,
• roof layers,
• materials,
• openings,
• curved edges.

Roof nodes and edges can also be edited to create more complex contours.

This parametric approach means that it is usually unnecessary to recreate a roof when the building design changes.

Complex roofs

Complex roofs should not necessarily be created as one single element.

A large or irregular roof can often be modeled more efficiently by combining several roof elements or individual roof planes.

This approach is useful for buildings containing:

• intersecting roof volumes,
• different ridge heights,
• different roof slopes,
• extensions,
• towers,
• dormers,
• entrance roofs,
• traditional complex roof structures.

Breaking a complicated roof into logical components usually makes the BIM model easier to edit and maintain.

Roof openings and roof windows

Openings can be created in roof surfaces when required.

These may be used for:

• roof windows,
• skylights,
• shafts,
• chimneys,
• technical openings,
• other elements passing through the roof.

Roof windows can also be placed directly on roof planes.

Their position follows the geometry of the selected roof surface.

Layered roofs

A roof can represent a multi-layer building construction instead of a single homogeneous element.

The layers describe the physical build-up of the roof.

Each layer can have its own:

• thickness,
• material,
• position within the structure.

Layered roofs provide a more accurate representation in sections and construction documentation and make it possible to model the actual building assembly rather than only its external geometry.

Roof structures

The architectural roof surface and the supporting roof structure are related but different parts of the model.

ARCHLine.XP can generate and model structural roof components such as:

• rafters,
• eaves purlins,
• intermediate purlins,
• ridge boards,
• collar beams,
• battens.

The architectural roof defines the overall roof envelope, while these elements represent its supporting structure.

For complex timber roofs, additional Beams, Columns and custom-profile elements can also be used.

Roof accessories and connected elements

The roof frequently interacts with other building components.

Typical examples include:

• gutters,
• downspouts,
• roof windows,
• solar panels,
• chimneys,
• walls trimmed to the roof,
• columns and structural supports.

These elements can be added after the main roof geometry has been established.

A practical workflow is therefore to create and verify the main roof first and add secondary components afterwards.

Roof quantities

The BIM model can also provide information for quantity takeoff.

Roof-related quantities can include the size of roof surfaces and information about structural roof components.

This information can support:

• material estimation,
• cost calculation,
• preliminary construction planning.

Recommended workflow

For most architectural projects, the following workflow is recommended:

1. Create the building walls

2. Choose the appropriate roof creation method

3. Define the footprint or individual roof planes

4. Set slopes, gable ends and overhangs

5. Check ridges, hips and valleys in 3D

6. Define the roof layers and materials

7. Add openings and roof windows

8. Add roof structures and accessories

9. Check the roof in sections and elevations

10. Generate documentation and quantities

For complex roofs, work from the main architectural form toward smaller details. Establish the overall roof geometry first and add structural and secondary components only after the main geometry is correct.

Choosing the right roof creation method

The following rule can help you select the appropriate method:

For most residential and architectural projects, Roof by Footprint is the recommended starting point.

Use individual roof planes when more geometric control is required, and Roof by Extrusion when the roof form is primarily defined by its cross-sectional profile.

Summary

The Roof tool in ARCHLine.XP is not limited to creating a simple roof surface. It provides a parametric BIM workflow covering the complete process from the initial architectural roof geometry to detailed layered constructions and supporting roof structures.

The three main modeling approaches are:

Roof by Footprint – create a complete roof from a closed boundary.

Roof by Plane – create and combine individually controlled roof surfaces.

Roof by Extrusion – create special roof forms from a cross-sectional profile.

Together, these methods make it possible to model anything from a simple flat or gable roof to complex multi-plane, curved and traditional roof structures while keeping the model editable throughout the design process.