How to model a Building Envelope with an architectural BIM Design software

An architectural project in a BIM software can be acheived by drawing various types of objects: building envelopes, doors, windows, stairs, etc., by means of a 2D and/or 3D input.
In a BIM software, unlike what happens with traditional CAD technology, the objects used for modelling are “smart objects” and not simple lines. “Smart objects” have their own specific physical and functional information and can be automatically displayed in 3D or 2D. This information, for example, can regard the material layer composition, geometry and mechanical characteristics, etc. The use of these objects allow to obtain a three-dimensional representation of the building model and a conseguent information system of the building as a whole and of each of its components.
In particular we will see how to define a building envelope using a BIM for architectural design Edificius by ACCA software.

The building envelope is a vertical building element type: it can be a wall, a partition wall, etc. In general, the building envelope is an element widely used to delimit rooms and compartments and define volumes and surfaces.

Building envelopes can be modelled in various ways in Edificius.

Figure 1: selecting the building envelope BIM object

Of course any design process must allow “free-hand” drawing: simply select the wall object and keep the left button mouse pressed to graphically define inclination and length. Alternatively, after specifying an inclination, you can define a length by typing in a value from the keyboard.

building envelope direction and length

Figure 2: defining length and inclination of the building envelope

To speed up the modelling process, you can even use a typical 2D CAD drawing to use as a floor plan background to trace upon. These CAD files can be in either the dxf or dwg file format.
An optimal solution when dealing with old project or survey files to quickly define the area and floor plan layouts to comfortably position our BIM objects. The ability to draw without having to dedicate too much effort makes the input process (of drawing objects) very fast and efficient.
To place a floor plan, all you need to do is simply load the CAD file using the “DXF/DWG CAD drawing” feature; this activates a dialog for selecting the CAD file.

insert floor plan

Figure 3: inserting the floor plan

At this stage, Edificius is capable of generating the BIM objects automatically by specifying their position on the DXF or DWG CAD file. Activating the auto-recognition tool is very straightforward and saves the user from having to go through tedious set up processes. You simply select the BIM object to insert, in this case we’ll start off from the “Building Envelope”, and then simply activate the “DXF/DWG” option on the multi-function toolbar to switch to auto-detect mode changing the mouse cursor to a magic wand.

auto recognition

Figure 4: activating the automatic recogintion feature

With the magic wand active, all you need to do is simply “touch” the background drawing. By tracing across the two straight lines that represent the 2D walls in the DXF/DWG CAD drawing, the corresponding 3D BIM object is automatically generated acquiring wall length and thickness directly from the CAD drawing.

object generation

Figure 5: automatic object generation

Another feature that can help speed up building envelope definition is the 2DMagneticGrid.
This very useful drawing aid allows us to define a customizable grid by inserting different grid types and sizes and combine them together to form very complex 2D shapes. To draw a grid just select the 2DMagneticGrid object and place it into position with a left mouse button click. This activates a contextual dialog box in which you can specify its geometry in rows and columns.

Magnetic grid

Figure 6: use of the Magnetic Grid

Once the first grid is inserted, you can then carry on inserting others so as to obtain the desired grid shape. By activating the Building Envelope BIM object again, you can now trace it following the 2D Grid intersection nodes that also serve as snap points making a “free-hand” drawing process very fast but also very precise.

inserting building envelopes

Figure 7: building envelope insertion

Although we’re using a 2D grid, we can still take advantage of the magic wand and activate the auto-recognition mode to insert the building envelope entities.

object recognition

Figure 8: the object recognition feature

To automatically draw the building envelope entites, you now simply select the “2DMG” function from the toolbar and then trace a selection rectangle around the previously defined grid.
These newly inserted BIM objects all have specific selection grips. These allow the user to instantly modify some of their geometrical characteristics. For a building envelope object type, the grip enables the user to change direction, length and alignment axis.

object characteristics

Figure 9: editing the object’s characteristics

From the “Properties” toolbox, other object characteristics can also be defined. The program’s object catalogue, also allows the user to choose from various material layer types or even define personalised ones.

material layer selection

Figure 10: choosing a material layer

Some keys of the keyboard keys speed up drawing operations, such as “”><“, with which you can set the start or end point of an object at a certain distance from a point.
The building envelopes are cut automatically for added versatility. At this stage, any unnecessary segments of walls can be easily deleted to finish off modelling with precision. Using the curved building envelope simplifies definition of curved wall sections with a specific object grip feature to set its radius and curvature.
In 3D view, you can see the objects drawn so far; making changes at this stage, modifying objects or adding others, is immediate and the user has full control over the entire model.

involucro fnale

Figure 11: the final result

Click here to download Edificius, the ACCA software solution for Architectural BIM Design