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Roof Framing Rafters

Revit Extensions – Timber Rafter Generator

This generator will place timber rafters into your model based on a selected Revit Roof element.

User Interface

The User interface provides a number of Framing Member situations…
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A preview layout is shown to make user modification before OK to generate the assembly. You can click into each sloping plane area and make specific specification for each one.
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Rafters

You can select ‘normal’ sizes (bulk timber, not NZ MSG) and enter minimum spacing.
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End Cut

The End Cut (they call it Tail Type) can be Plumb, Square and Plumb and Level cut.
But the ‘C’ value for the under soffit cut is a bit awkward – not a finished face distance.
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You can even override any individual rafter sizes in a summary table interface…
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What doesn’t apply…

Hips and Valley

Hips and Valley boards are assumed to be heavy lumber with chamfered top edges.
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But you can specify say a 20 x 150 member and correct it later as a square profile.
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Ridge Boards Beams

Ridge Board / Beam options are better… the Ridge board option with a narrow profile does the trick.
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Collar Ties

Adding Collar Ties is interesting in that you can specify the top side edge above your floor reference Level, but again to be useful one needs to work down the Depth of the member for a ceiling height.
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Purlins

Finally you can add Purlins, but these are what we refer to as Under Purlins (not cladding fixing purlins).

RevtExtensions2013-RoofFraming10The Results

Once you are done with adjusting member sizes just click OK and the Structural Members are generated ‘within’ the previously select Roof element. Then change your Roof Type to represent just the cladding Purlins and Cladding material.
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Bugs ?
It gets a bit mixed up as to how the underside of the end cuts should be, I specified Plumb and Level cut with a C=50mm distance, but ended up with members oddly cut.
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As like many other Revit Extension generators, you cannot edit the finished result back at the initial Revit Framing dialog so apart from changing individual Structural Framing members, you will have to start over if too many items are just not appropriate.
On the good side a nice touch is the dialog remembers your last size values when you do a retry!

What’s Missing

There is no facility to have the rafters notched over a wall top plate so you cannot use Assemblies and document each cut member! But as a modeling tool it is OK for creating exposed rafters.
Oh yes you will have to make any cladding fixing Purlins manually.
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There is also a Truss Generator  – but we will leave generation of those to the roof truss fabricator, to work out once the job is underway.
 
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