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How do I model a Saltbox Roof (Asymmetric gable)?


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Hi folks,


I'm preparing a model of an existing house which will have an addition added to and it has a saltbox style roof (asymmetric gable). I've attached some images of a building section, roof plan and elevation for reference. The second floor steps back and is about half the width of the main floor, resulting in a roof that spans from the top of the wall at the second floor to the top of the wall at the first floor, forming a double height volume resulting in the asymmetric gable.


What is the best way to model this roof that allows me to add the gables and skylights easily? I don't need a lot of detail in the roof object, as the existing house will be treated as a simple white object in 3-D. 




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I'm not sure of the best way, but this can be achieved using Clip Object to shape the roof.


Trace the roof plan, roof lines and footprint.


Basically construct the main roof with the differing bearing heights first as an imaginary roof that extends beyond the cut plane such that your ridge lands in the correct place.  Set your gables on this roof.  Next, use rectangles to clip the roof on the east side to the desired eave location.

You now have a roof as depicted in your section.


Use the same technique to cut out where the other intersecting roofs will exist on this main roof.  It should be looking nice and complicated now.


Then add those smaller roofs one at a time, stick then on a separate design layer from your main roof for the next step.


Use your building footprint to generate walls.


Select all the walls that should extend to the main roof and use "fit walls to object", selecting the main roof's design layer

Repeat this process for the walls that should extend to the secondary roofs, making minor adjustments to the walls as necessary.


The attached file kind of graphically breaks it down into steps to compliment the cutting description above.  I tried to use classes and design layers that are self explanatory, but I may have mixed a few thing up in my haste.  I also noticed that I missed trimming a piece of roof in this example.

Anyhow, hope it helps.  Should be pretty easy for you using this technique.  The longest part of the job was tracing the roof plan 😉





saltbox roof.vwx

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@MaltbyDesign No problem, not my finest moment in explaining 🙂  Here's an updated file with a little more information and steps, including the evolution of the roof forms with each editing operation.  It's pretty fast when approached systematically, especially if you are starting with 2D drawings.  Maybe one of the talented architects here on the forum will spill the beans on how they do roofs.

saltbox roof2.vwx

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An easy way - because the bearing heights and rafter lengths are different front and back is to use roof faces:


Plan View - draw a rectangles representing the front roof

AEC>Roof Face

Axis 0

Set the correct slope

Two clicks to draw the the 'bearing line' along the ridge line and a third click to denote the up-slope


repeat for the back roof

Move the roofs a hair apart and connect them at the ridge using the Connect/Combine tool.


Lift the roofs to the correct elevation



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That said, it is unfortunate that the person who drew these fairly ancient plans didn’t bother to note the roof pitches on the roof plan sheet. That makes things a bit more difficult in that you have to refer to the sections for that info....which in looking at your image of the section, those pitches are not even noted there,  from what I see. 


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I would be great to be able to create a roof based on bearing height + ridge height as well as bearing height + roof pitch, for circumstances such as this where you have the former information but not the latter. This was a Wishlist item I made about the Massing Model tool where I have site surveys with eaves heights + ridge heights of buildings but in order to create massing models of them I have to separately work out what the roof angle equates to for each one.

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9 minutes ago, MaltbyDesign said:

Thanks again for the tips, all. I think I've got the roof figured out but got bogged down again with Storeys and trying to model an existing home and figuring out existing and new construction. Back to 2D drawing in AutoCAD for this project. I think I'll reserve 3D for new builds only, for the time being.


Just curious.

Why AutoCad for 2d?

Why not Vectorworks

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A note regarding Stories... I never use them! IMO they only made the whole user experience more confusing. That said, I *think* (someone could correct me or verify) that Stories were added to facilitate BIM/ICF capabilities. As a small one-person operation specializing in one-off residential design I don't need those capabilities.


Also, IMO all the "automated" drawing/file setup tools are dangerous as they prevent the user from learning the basics of Layers and Classes and how to set up a file manually, which is really easy in most cases. Again speaking from my experience and needs. Large projects with multiple users are a different story (pun??).

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I do not find it Automated.

One still needs to Manually enter Layers, Classes, Levels.


Then, one is able to use what they have setup.


I still have drawings when I used layers, classes only.

Still had to manually enter all those.


This is all part of good Design.

I recall from years ago when were going to frame a house we would layout a Story Pole of the house.

Floor Joists (1st Story)

Shoe Plate

Cripple Studs

Window Sill plate(s)


Top Plates

Floor Joist (2nd Story)

Cripple Studs

Shoe Plate

Window Sill plate(s)


Top Plates


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