Wednesday, 19 May 2010

Components for Existing Building Surveys in Revit

Using Revit for Surveys: A different approach to modelling in Revit is required when it comes to existing buildings. For instance, depending on the age and design of the building, a site survey would probably result in no two windows being exactly the same size. This raises the question “Should I create window types for every existing window?” Depending on the size of project and the scope of works involved this could mean hundreds of types. Consider what the purpose of the survey is and how the windows will be manipulated in the proposed design i.e. Are the windows being replaced? or just generated for model integrity and aesthetics? There could be numerous outcomes.

Example: Instance Based Window Family

One of the methods I have used to combat this with items such as doors and windows is by generating families with instance-based parameters. In the following example we take a look at a typical window family and how we can change the way it works to in a measured building survey.

In this example we start with a window family from the standard Autodesk Library called ‘Sgl Plain.rvt’

If we want this to be an instance-based window family (i.e. able to control the width and height without having to create a new instance every time), then we need to change the parameters from Type to Instance.

Ok, so we have hit our first problem. The standard Autodesk Window category will not allow you to ‘Modify’ the Width or Height parameters so how can we change this?

…Well here’s a little work around:

In 2010 or 2011, Go to the Create Tab > Category & Parameters and set the category as something such as Generic Model and click OK.

Now go back into the Types and you will notice that the Width and Height can be modified.

Change Rough Width & Rough Height to Instance Parameters first, then the Width & Height. Now go back to the Category & Parameters and set it back as Windows.

Tada!   You now have an instance based window!

The example I have modelled here has a few additions to make the survey modelling process a little easier:

Reveal Setback:
More often than not, building surveys require both an internal and external measured survey. The external width of the window is measured from reveal-to-reveal, and also the inside edge from reveal-to-reveal. There is always a difference between the two measurements due to internal plasterboard or other finishes. I call this tolerance the ‘reveal setback’ as shown here.
This is also modelled as an instance parameter so the user can stretch these to suit each individual window.

Another key point to remember is that it is very awkward to stretch the windows when their origin is set to the centre. For survey windows I would recommend changing the origin (setting out point) to the left or right hand external reveal. You can do this by looking at the element properties of the reference plane and checking ‘Defines Origin’.

Splayed reveals:
If you need splayed reveals (internally or externally), you will need to delete the default opening which is located on the back face of the window.

If you do this, you will no longer have an opening in your wall so you will need to create a void extrusion or sweep to create the desired window shape (this is required for any customised reveal opening).

In my example I have used 4 Extrusions: 1 for the external opening width, 1 for the internal and two triangular fillets for the splayed reveals. Depending on your requirements you may want to change how you do this.

I have also removed the cavity closer parameters and wrapping parameters to reduce the file size and make sure the parameter list is not looking overcomplicated.

TIP: Create a Default Wall Material and set the colour to grey and transparency to 50%. This will make it much easier to see what is going on with the 3D geometry as it passes through the wall.

As with any modelling program there is more than one way to approach a task like this. Other ways would include modelling windows as ‘Create In-place’ objects, or just using the normal ‘Type based’ windows. In-place would be my second choice but remember these aren’t reusable in other projects and they will mean you have to start from scratch every time! Type based windows can be used in some instances but just be aware of how many different Types you will need to create. If you only need 5 – 10 Types then maybe this is the better option? My experience would be that if you have a basic kit of instance based survey windows, doors which can be used in most situations, this is the most efficient and productive way of generating survey models again and again.

If you have any other suggestions for building surveys I would like to here from you.

Here is the sample Revit Family rfa file used in this blog. It’s modelled in Revit 2009 so any legacy Revit users can also view it.

Sample Revit Family: Survey-type Window Sgl Plain-IntSplay.rfa

1 comment:

Anonymous said...

Thanks very much for the family & tutorials; keep up the good work!

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