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How to model mansard roof and walls in Vectorworks


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How would you approach the modelling of this mansard roof and walls?


They're construction drawings, so need to show correctly detailed in plan and section. I was wondering about drawing the walls in plan view with no z-height, and then modelling the mansard roof and walls with the roof tool... and may slicing through it in plan somehow to show extent?

Screen Shot 2017-11-23 at 11.00.06.png

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This is a problem I am continually wrestling with as I have recently been doing several projects that involve loft conversions and/or other work on existing buildings that are complicated in 3d, with split levels, intersecting pitched roofs and so on. As I linked to on the other discussion, here is a thread I made when I first started trying to work out how to do things using a 3d model (up until then I'd effectively been doing everything manually in 2D):




That was a couple of years back; in the meantime, I have developed a method of sorts but it's far from tidy. You might be interested in looking at this screen recording where I try and show how a more recent drawing is structured. You can see that at both of the floor levels I show, I've got a combination of a horizontal section and a top/plan view. Each cropped to odd shapes to the fit together into the final drawing. There is a certain amount of patching-up (hiding lines that shouldn't be there, and so on) that I do in annotation space.


This drawing makes use of auto-hybrids to an extent. (NB towards the end for example that this is how I've created the party walls at loft level where they have to follow the profile of the roof, and incorporate chimneybreasts - trying to draw these using the wall tool was just too much hassle and unstable). However, I've since stopped using autohybrids because I have found they create too many new problems. Mainly to do with ease of editing, because it's difficult to move elements in and out of them due to the fact they have their own internal XYZ system. So elements that in this drawing example were autohybrids, visible in the top/plan portion of my composite drawing, I'm now more inclined to simply model directly and include in the horizontal section portion. This means that when I get to loft level, hardly any of the final plan is generated using top/plan - in fact it might literally be cropped right down to just a couple of doors and part of a partition wall.


Top/plan is also not much good at showing things that have been directly modelled, on lower stories, in top view. In this drawing an example is the roof of an existing victorian ground floor bay window, which I want to see in my first floor plan. This had to be directly modelled as there's no hope of using the standard VW window, wall and roof tools to create something that sufficiently resembles the reality. So the top view of this is included in my horizontal section viewport crop.


I'd certainly like to find a less labour-intensive way of dealing with these kinds of situations. It perhaps helps explain why I think we urgently need a rethink of how plans are generated. We need an "intelligent" horizontal section method. One that can section through solid modelling elements as well as parametric elements like doors and walls and produce a sensible and reasonably customisable result.


Anyway here is the screen recording. Don't know if any of this makes sense to anyone else. Happy to answer any questions.




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3 hours ago, Christiaan said:



They're construction drawings, so need to show correctly detailed in plan and section.


My current approach:


Draw the basic model as accurately as possible, but don't expect to be able to use it for drawings any more detailed than 1:50, and possibly not even showing things like wall and roof components at that scale, because it's just too much faff to persuade them all to join correctly (certainly for anything to be used as construction drawings).


So, for scales larger than that, revert to the old 2D drawing methods, but use the basic model in the background as a reference to keep things co-ordinated, and as a quick way to get the right section geometry - in other words, trace off section viewports. This at least saves the time it takes to project section geometry manually. But of course, updating the 3d model won't automatically update all your large scale, traced, detail drawings.


I should say that the projects I've currently got at construction stage are ones drawn with the "old" method - all 2D. The ones I've got drawn up in 3D have only got as far as planning stage, so I haven't yet really tested the method I describe above, for progressing beyond 1:50 scale, on a "live" project.


I've seen from your other threads in the past, that you've done pretty well at generating construction sections showing wall/floor buildups and so on (in fact I watched your presentation at the VW BIM day in London a year or so ago). However I've noted that those designs are all fairly rectilinear. Things really start to get tricky when you get involved in pitched roofs, split levels and so on. There's a reason the example that the VW people presented at that same BIM day was called something like "cube house" or similar.

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  • 2 weeks later...

Hi Christiaan,


Here's how i would approach creating this:




in this approach, the walls would be on the third floor layer

the roof and the slab would be on the roof layer.


In this approach, you would control how much of the right side wall projection (mansard) is visible through the cut plane option in the edit design layers panel.


Let me know if that makes sense

Edited by wingchudesign
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- how would you draw the dormer cheeks?

- how to make the dormer cheeks join properly with the roof and wall elements?

- would VW know to cut the dormer cheeks at the right height?

- can the slab you use for the ceiling have angled edges to meet the roof neatly?


My view is that making all the above work (especially if wall/roof components are to be shown), if it's even possible, would probably be more time consuming and less easily editable than just doing it all as directly modelled solids.


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Hi Christiaan. Just saw your post and remembered how I struggled with a similar roof. After playing around with the revolve with rail tool for a while I reverted to using a v thin roof and then backing it up with extrudes for the internal shell. It was very a painful learning curve :-) I also admit it wasn't very tidy but it did the trick as it looked ok from the outside. The added complexity is you need to get this done for working dwgs.  Any way I shared my pain !!  See the right picture which I updated as I had a closer look as to how I did it! ( I cant seem to remove the left image)




Edited by David S
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Thanks for the feedback everyone.


@line-weightis on the money. To produce a section that show components is not feasible. I think it would require modelling the both the upper roof and the sloping walls with freeform objects of various kinds and then creating Auto-hybrid(s). The sloping walls are simple enough (as an EAP) but the upper roof has hips and valleys and would require a lot more work. 


The problem is freeform objects don't work well with parametric objects. Neither understands the other.


I also tried using Roof Faces for the sloping walls, but there's just no way to configure the correct edge conditions. 


So I think I'm going to resort modelling the slate tiles only (with Roof and/or EAPs) and drawing the rest in 2D on the Annotations layer. Bit of a disappointment.


The attached screenshot shows upper roof as a Roof object and sloping walls as a series of EAPs.



Edited by Christiaan
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We've been struggling with a similar roof recently. Dead ends everywhere except for 2d-drafting. One of the issues was dormer window "walls" - in real life they have a wall not roof structure.


Being able to give components to extrudes would be great. Not sure if it is possible to program though.


Any deviation from simple geometry results in a swamp of bim/3D/2D with no clear solution. This is not to say VW is alone in this - all major software packages struggle with this. Some programming and mathemathical breakthrouh is clearly required.

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I'd consider doing away with floors/walls/roofs as different types of object altogether. Have something called a "planar buildup", say, to reflect the fact that much of building construction is made of layers of different materials/systems. Have a bunch of entity types that automatically create holes in those planar buildups. Probably no reason to distinguish between a door and a window either, in programming terms.


Then generate plans by cutting through the actual geometry, instead of trying to guess what the vertical position of things is according to their object type, and forcing users to have to decide whether calling a mansard a wall or a roof is going to create the least headache.

3 hours ago, JMR said:

VW is alone in this - all major software packages struggle with this. .


That, in a way, is sort of encouraging to hear!

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Something like the "planar buildup" you mentioned could be a good solution. Different priorities for "buildup" layers: similar components join automatically etc.


One thing I've wondered is that why it is not possible to stretch wall components (or any components) in live section - creating details from the BIM model would be a breeze, were that possible. Currently one has to go through complicated settings to achieve this.





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18 minutes ago, JMR said:

Something like the "planar buildup" you mentioned could be a good solution. Different priorities for "buildup" layers: similar components join automatically etc.


One thing I've wondered is that why it is not possible to stretch wall components (or any components) in live section - creating details from the BIM model would be a breeze, were that possible. Currently one has to go through complicated settings to achieve this.





Doing it in section would presumably create questions about how much of the wall you want it to affect. For example, a wall which steps up along its length. Would the change apply just to the section of wall which was the same height as where the section was cut, or would it apply proportionately to the whole wall? It would be necessary to have very clear control over stuff like this so as not to accidentally mess up other details. I'd also want to feel secure that changes I made were persistent - and that the wall wouldn't at some point in the future decide to do an automatic join, when I adjusted it in plan or whatever. I don't feel secure about this at the moment, using wall elements. There needs to be a clear opt-out of things happening automatically, when you don't want it, because those automatic joins often don't reflect the reality of constrction detailing. For example, those 45 degree bevelled edges you end up with if you join two walls of different heights (maybe this has been fixed since I last played around with this?)

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planar buildup object sounds great.


12 hours ago, JMR said:

This is not to say VW is alone in this - all major software packages struggle with this.


As I understand it modelling this would be reasonably straight forward in Archicad, which has support for multi-plane roofs, providing both the mansard and dormer capabilities.

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By the way, it seems to me there's a niche for someone to fill, in doing proper, in depth comparison reviews of the main software packages. Ones that really go into the sort of stuff we discuss on here. Most of the CAD reviews I read are not very good. They'll discuss the "new features" and so on but they don't ever seem to raise the issues that for me are the ones that I struggle with day-to-day, which are all the situations where you're trying to get the software to do something that it doesn't provide for easily.


I'm always wondering whether these same problems exist in other software. I can't really find out for myself because of the huge investment in time it would take to learn something like Archicad to a similar level of familiarity as that which I have with VW.


Someone needs to make it their thing to do these comparisons...but it needs to be someone who has real-world experience in the range of scenarios in which the software is likely to be used. Perhaps an impossible task!

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Back in 2009 we were working on a complex building in AC. The walls were slanted (not vertical) and on 90 degrees in plan either. We had pretty massive difficulties with doors etc...however, a long time has passed since, I'm not fully aware of the current situation.

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As far as I know, Archicad has tilted Walls and even Walls from a Profile like an EAP.

And I think their PIOs and some other thing related to Architecture are superior over VW.


However in VW you can manually model mostly any geometry that happens in Architecture.

Like in the cases above. You can create 2D section drawings from that and you can assign

IFC Tags for IFC exports.

It is just not as comfortable as VW's PIOs - as long as they are suitable.

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41 minutes ago, line-weight said:

Is manual modelling more restricted in Archicad, then?


I don't think so - in Architecture.

They put all that Modeling into a single Tool called Morph (?)

that does all typical Sketchup things, which is quite capable.


I think it does not have the (tedious for me) NURBS Surfaces

or SubD to go really freeform.

But it is not like many assume that you still need the Slab Tool

to model a table desk and such things.




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It is different than VW and I am not sure where and how much it is more limited

than VW in modeling. I tested it a bit deeper in 2010 and did some Tutorials +

"real" Test Projects. I looked at it again after the new UI came with V20 (?) and

played a bit with the Morph and saw some Videos about it.


I mainly did some quick tests about all things that annoyed me in VW over

the years and all that wasn't an issue in Archicad at all.

But I did not test so far what Archicad could have for own issues that would

annoy me over the years ;)


I think if I had to do competition designs and 2D presentations, I would prefer VW.

If I would need standard Architectural BIM and plan output, I would go Archicad.

Of course you could do either with both of them but there are slightly differences

and capabilities that make both more or less suitable for your projects and your


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