Tutorial by: Mr Spot
August 18, 2004

25.   Here comes the fun part we now need to create a formula so revit will calculate the number of louvres to use in given situations. Begin by going to your family types (you may wish to enlarge the window so you have more space to view your formula information). First, create a parameter by clicking add and make a new length parameter called "Free Air" this will become the spacing of our louvres. Now give this parameter a value (eg: 20mm).

26.   Now add another parameter called Louvre Height using the same method as the Free Air parameter. We need to this to calculate the vertical height of the louvre for set angles and louvre depths/thicknesses. This requires so knowledge of Pythagoras and basic trigonometry. The formula for the louvre height should work out as below (this step is not essential but shortens the formula we need to specify the number of louvres:

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27.   Now we can add formula information to the No of louvres parameter as detailed below. Revit will now calculate exactly how many louvres we require to achieve a specified free air gap, louvre depth and angle.

(click to enlarge)