Arch tutorial

Work in progress - do not translate yet!

Introduction
This tutorial aims at giving you the basics to work with the Arch Workbench. I will try to make it simple enough so you don't need any previous experience with FreeCAD, but having some experience with 3D or BIM applications will be useful. In any case, you should be prepared to look for yourself for further information about how FreeCAD works on the FreeCAD documentation wiki and tutorials. On youtube you will also find a lot of FreeCAD tutorials.

The purpose of the Arch Workbench is to offer a complete BIM workflow inside FreeCAD. As it is still under development, don't expect to find here the same tools and level of completion as grown-up commercial alternatives such as Revit or ArchiCAD, but on the other hand, FreeCAD being used in a much bigger scope than these applications, the Arch Workbench greatly benefits from the other disciplines FreeCAD caters to, and offers some features rarely seen in traditional BIM applications.

Here are, for example, a couple of interesting features of FreeCAD's Arch Workbench that you'll hardly find in other BIM apps:


 * Architectural objects are always solids. From FreeCAD's strong mechanical background, we learned the importance of always working with solid objects. This ensures a much more error-free workflow, and very reliable boolean operations. Since cutting through 3D objects with a 2D plane, in order to extract sections, is also a boolean operation, you can immediately see the importance of this point.


 * Architectural objects can always have any shape. No restrictions. Walls don't need to be vertical, slabs don't need to look like slab. Any solid object can always become any architectural object. Very complex things, usually hard to define in other BIM applications, like a floor slab curving up and becoming a wall (yes Zaha Hadid, it's you we're talking about), present no particular problem at all in FreeCAD.


 * The whole power of FreeCAD is at your fingertips. You can design architectural objects with any other tool of FreeCAD, such as the PartDesign Workbench, and when they are ready, convert them to architectural objects. They will still retain their full modeling history, and continue totally editable.


 * The Arch Workbench is very mesh-friendly. You can easily design an architectural model in a mesh-based application such as Blender or SketchUp and import it in FreeCAD. If you took care of the quality of your model and its objects are non-manifold solid shapes, turning them into architectural objects only requires the press of a button.

At the time I'm writing this, though, the Arch Workbench, as the rest of FreeCAD, suffers some limitations. Most are being worked on, though, and will disappear in the future.


 * FreeCAD is no 2D application. It is made for 3D. There is a reasonable set of tools for drawing and editing 2D objects with the Draft Workbench and Sketcher Workbench, but it is not made for handling very large (and sometimes badly drawn) 2D CAD files. You can usually successfully import 2D files, but don't expect very high performance if you want to keep working on them in 2D. You have been warned.


 * No materials support. FreeCAD will have a complete Material system, able to define very complex materials, with all the goodies you can expect (custom properties, material families, rendering and visual aspect properties, etc), and the Arch Workbench will of course use it when it is ready.


 * Very preliminary IFC support. You can already import IFC files, quite reliably, provided IfcOpenShell is installed on your system, but exporting is still not officially supported. This is worked on both by the FreeCAD and IfcOpenShell developers, and in the future we can expect full-powered IFC support.


 * Most Arch tools are still in development. That means that automatic "wizard" tools that create complex geometry automatically, such as Arch Roof or Arch Stairs can only produce certain types of objects, and other tools that have presets, such as Arch Structure or Arch Window only have a couple of basic presets. This will of course grow over time.


 * Relations between objects in FreeCAD are still not officially available. These, for example the relation between a window and its host wall, are currently implemented in the Arch Workbench with temporary (and therefore somewhat limited) methods. Many new possibilities will arise when this feature will be fully available.


 * Units are being implemented in FreeCAD, which will allow you to work with any unit you wish (even imperial units, you guys from the USA can be eternally grateful for this to Jürgen, FreeCAD's godfather and dictator). But at the moment the implementation is not complete, and the Arch workbench still doesn't support them. You must consider it "unit-less".

Typical workflows
The Arch Workbench is mainly made for two kinds of workflows:


 * Build your model with a faster, mesh-based application such as Blender or SketchUp, and import them in FreeCAD in order to extract plans and section views. FreeCAD being made for precision modeling, at a much higher level than what we usually need in architectural modeling, building your models directly in FreeCAD can be heavy and slow. For this reason, such a workflow has big advantages. I described it in this article on my blog. If you care to model correctly and precisely (clean, solid, non-manifold meshes), this workflow gives you the same performance and precision level as the other.


 * Build your model directly in FreeCAD. That is what I will showcase in this tutorial. We will use mostly three workbenches: Arch, of course, but also Draft, whose tools are all included in Arch, so there is no need to switch workbenches, and Sketcher. Conveniently, you can do as I usually so, which is to create a custom toolbar in your Arch workbench, with Tools -> Customize, and add the tools from the sketcher that you use often. This is my "customized" Arch workbench:



In this tutorial, we will model the house in 3D, based on the 2D drawings we'll download from the net, and extract from it 2D documents, such as plans, elevations and sections.

Preparation
Instead of creating a project from scratch, Let's take an example project to model, it will save us time. I chose this wonderful house by Vilanova Artigas (pictures by the famous Pedro Kok), because it is close to where I live, it is simple, it's a wonderful example of the amazing modernist architecture of São Paulo (it is even for sale if you have "a few" Reals to spend), and dwg drawings are easily available.

We will use the 2D DWG drawings obtained from the link above (you need to register to download, but it's free) as a base to build our model. So the first thing you'll want to do is to download the file, unzip it, and open the DWG file inside with a dwg application such as DraftSight. Alternatively, you can convert it to DXF with a free autility such as the Teigha File Converter. If you have the Teigha converter installed (and its path set in the Arch preferences settings), FreeCAD is also able to import DWG files directly. But since these files can sometimes being of bad quality and very heavy, it's usually better open it first with a 2D CAD application and do some cleaning.

Here, I removed all the detail drawings, all the titleblocks and page layouts, did a "clean" ("purge" in AutoCAD slang) to remove all unused entities, reorganized the sections at a logical location in relation to the plan view, and moved everything to the (0,0) point. After that, our file can be opened quite efficiently in FreeCAD. Check the different options available in Edit -> Preferences -> Draft -> Import/Export, they can affect how (and how quickly) DXF/DWG files are imported.

This is how the file looks after being opened in FreeCAD. I also changed the thickness of the walls (the contents of the "muros" group), and flipped a couple of doors that were imported with wrong X scale, with the Draft Scale tool:



The DXF importer (which also takes care of DWG files, since when importing DWG files, they are simpl converted to DXF first), groups the imported objects by layer. There is no layer in FreeCAD, but there are groups. Groups offer a similar way to organize the objects of your files, but don't have specific properties, like AutoCAD layers, that apply to their contents. But they can be placed inside other groups, which is very handy. The first thing we might want to do here, is to create a new group (in the tree view, right-click on the document icon, add a group, right click on it to rename it as "base 2D plans", and drag and drop all the other objects into it.

Building the walls
Like most Arch objects, walls can be built upon a big variety of other objects: lines, wires (polylines), sketches, faces or solid (or even on nothing at all, in which case they are defined by height, width and length). The resulting geometry of the wall depends on that base geometry, and the properties you fill in, such as width and height. As you might guess, a wall based on a line will use that line as its alignment line, while a wall based on a face will use that face as its base footprint, and a wall based on a solid will simply adopt the shape of that solid. This allows about any shape imaginable to become a wall.

There are different possible strategies to build walls in FreeCAD. One might want to build a complete "floor plan" with the sketcher, and build one, big, wall object from it. This technique works, but you can only give one thickness for all the walls of the project. Or, you can build each piece of wall from separate line segments. Or, this is what we will do here, a mix of both: We will build a couple of wires on top of the imported plan, one for each type of wall:



As you see, I've drawn in red the lines that will become concrete walls (a pictures search of the house can help you to see the different wall types), the green ones are the exterior brick walls, and the blue ones will become the inner walls. I passed the lines through the doors, because doors will be inserted in the walls later, and will create their openings automatically. Walls can also be aligned left, right or centrally on their baseline, so it doesn't matter which side you draw the baseline. I also took care on avoiding intersections as much as I could, because our model will be cleaner that way. But we'll take care of intersections later.

When this is done, place all those lines in a new group if you want, select each line one by one, and press the Arch Wall tool to build a wall from each of them. You can also select several lines at once. After doing that, and correcting widths (exterior walls are 25cm wide, inner walls are 15cm wide) and some alignments, we have our walls ready:



We could also have built our walls from scratch. If you press the Arch Wall button with no object selected, you will be able to click two points on the screen to draw a wall. But under the hood, the wall tool will actually draw a line and build a wall on it. In this case, I found it more didactic to show you how things work.

Did you notice that I took great care not to cross the walls? this will save us some headache later, for example if we export our work to other applications, that might not like it. I have only one intersection, where I was too lazy to draw two small line segments, and drew one big wire crossing another. This must be fixed. Fortunately, all Arch objects have a great feature: you can add one to another. Doing that will unite their geometries, but they are still editable independently after. To add one of our crossing walls to the other, just select one, CTRL + select the other, and press the Arch Add tool:



On the left is are the two intersecting walls, on the right the result after adding one to the other.

An important note about parametric objects

Something is important to consider already. As you can see, in FreeCAD, everything is parametric: Our new "united" wall is made from two walls, each based on a baseline. When you expand them in the tree view, you can see all that chain of dependencies. As you can imagine, this little game can quickly become very complex. Furthermore, if you already know how to work with the sketcher, you might have wanted to draw the baselines with constrained sketches. This whole complexity has a cost: it raises exponentially the number of calculations that FreeCAD has to perform to keep your model geometry up to date. So, think about it, don't add unnecessary complexity when you don't need it. Keep a good balance between simple and complex objects, and keep these for the cases where you really need them.

For example, I could have drawn all my baselines above without caring about what crosses what, and fix things with the Arch Add tool later. But I would have raised much the complexity of my model, for no gain at all. Better make them correct right from the start, and keeping them as very simple pieces of geometry.