# Hyperbolic Paraboloid Roof

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Hi,

I'm designing a building which is based on a simple barn extrusion, however this is complicated through the building fanning out in plan and an angled pitch of the roof. Please see attached screen shots. I believe the change in angle and height of pitch is creating a very small hyperbolic paraboloid roof structure (if very small).

I would like to model this roof which allows for a fairly easy change as the project evolves (still in early feasibility stage). I am fairly new to modelling in 3D in Vectorworks (used to 2D) and would very thankful in any help in modelling this roof.

Many thanks,

Christina

Hi Christina,

the two roof faces do in fact appear to be hyperbolic paraboloids. This is because the pitch at the beginning of the roof (let's say 'small end') and the end of the roof are not the same -- or at least it appears that way from your elevation. I'm not sure how you have modeled this.

There are two general approaches to doing this:

Approach 1: Use "pure" solid / 3D modeling. Make the closed shed shape in elevation, taper-extrude it, extract the outer surface, and shell it.

Approach 2: Use architectural objects. Start with a roof plane. Draw it the way you want it in plan, set its pitch and play with its base-line to get the eave slope you like (you'll spend time in trial and error looking at this from various points of view). When you like it, mirror it along the sloping ridge. Then draw a couple of walls and use "Fit walls to Objects" command to get them to slope. You'll have to embed them in the roof objects to get the seamless look you want. The advantage of this approach is that you can use the Roof framer to get your rafters, etc.

Good luck and check back in!

I'm not sure if it is a good idea, in case of your non rectangular plan, to mix these 3 Levels of complexity :

1. Hyperbolic Paraboloids

2. Sloping Eaves

3. Sloping Ridge

I would expect that having one sloping eaves or one sloping ridge are used to avoid any Hyperbolic Paraboloids.

If you use both for design reasons I would still expect being used to avoid any Hyperbolic Paraboloids.

Or the other case, keeping the roof edges level and use Hyperbolic Paraboloids.

If you could live which such a design approach it would be quiet easy with an Multiple Extrude.

Draw the first End Profile and the second end Profile and Multi Extrude.

Just make sure to keep the same 2D Slope of the Roof Area for both Profiles.

You can go into Edit Mode and change your Profiles to play with points of ridge and eaves for their resulting

slopes.

Edited by zoomer

Hi Robert,

Yes, the two gable ends are different in both height and pitch (hence creating the hyperbolic paraboloid). The structure is modelled by drawing each rafter after corresponding heights from elevation and plan, as individual polygons, which have then been extruded and placed in the right location in plan.

I think I have already tried your second approach where the roof was modelled as a roof face to the right pitch - however, due to the two different angles of the pitch at either end this isn't possible. Are you suggesting to use the "Roof face" under the AEC menu?

Many thanks!

Ah, so you're saying you want the Hyperbolic Paraboloid (HP). OK. (I wasn't sure, because the visual effect was so small.) If you want that, then I would loft a profile of beginning 'barn profile' to the end 'barn profile'. Then I'd shell it. Now you have your main shape. To get the frames, draw a number of extrusions across the 'barn shape' and do a model:intersect solids (using a duplicate of your barn shape). It's easier to do than to describe. I've attached a sample file.

You are correct that you won't be able to get an HP using a roof face. Roof faces are strictly planar.

HP_shell.vwx

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