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Intersecting pitched roofs


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I know this has been raised before, in different variations, but I haven't found the answer to my specific issues. We have a project with several intersecting pitched roofs, that also meet/ overlap the walls. I am struggling to get the geometry to meet satisfactorily and would really like to be able to manipulate the roof faces with 3D handles. It seems that if i join roof faces, the cut line continues down at the angle of the intersection, rather than finding the wall that I also want it to meet. If I edit the roof face, this happens as if the roof face was a flat polygon, and when I exit the editor then issues with the junction between the roof faces arise. In these sort of scenarios am I better to abandon the create roof/ roof face tool and model as 3D solids of some sort (and not have the BIM roof build up available) or are there options that I haven't explored. As I understand it within Archicad roof vertices are editable in the same way as a 2D polygon, which would be very helpful here. In all the instances attached the projecting gable roof wants to come back to meet the wall of the main building below the gutter line of the main roof, whilst forming a neat valley at the junction of the roofs.

Thanks in advance for any assist.



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There are probably a few ways to deal with this, but for me (and old school kinda guy) Roof Faces are best dealt with by using the Add Surface and Clip Surface commands (which must be done in Top /Plan View). If the Roof Faces are the same pitch and bear at the same height, then it's all 45º angles. But when you have different pitches and/or different plate heights it gets a little tricky. There are two ways I know of to attack these problems: one is by using trigonometry. Yuck (personal opinion). The other is by using simple geometry (i.e.: measuring distances and applying to Roof Faces) Yay. In order to measure the distances, go to a straight-on Side (or whatever) View, in Wireframe, and set your prefs for Screen Plane (this will be temporary). You might also want to apply a temporary color to the particular Roof Face(s) you need to measure to make it easier to find (it can be really hard to see what's what in wireframe). So for example, pull a line from the end of the ridge to where it needs to intersect/touch. Remember the dimension(s). Go back to Top/Plan View and using the "magic number(s)" that you just discovered, draw a polygon (or rectangle, or parallelogram) and then use Add Surface or Subtract Surface. Don't be afraid, just make sure you have at least 20 Undo's set ;-) Once you do it a few times it'll become second nature. I hope that helps.

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Hi @mike-h,

I too do a similar workflow to Peter (above).  Roofs are tricky especially when 2 levels are combined or your covering odd shaped areas of a design.  All things are possible "in general".

I like to draw my roofs first in top/plan view by simply using lines/polygons; getting my soffit depths set as well as all my angles.  I then draw my roof polygons and create "Roof Faces".  On complex roofing situations this initial layout does change.  I may have to switch to an elevation view like Peter mentioned and get a more precise distance from an number of points of reference.


Just a little tip/trick to get your plan angles correctly when using multiple roof slopes is to create a rectangle using the roof slope as a distance for 2 sides of the rectangle.  Use the opposing roof slope for the other two sides.  See pic attached.  Join with a line one corner to an opposite corner and you have your angle.

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  • 3 weeks later...

Thanks all for the replies, I've been off the project for a few weeks but back on it now. Working through the suggestions. I had already watched your video Alan, thanks for posting it, but I have to say I find the snapping of the 3D polygon tool unsatisfactory - certainly compared to sketchup where intersections between a line and a planar object are very clear. For example in VW if I try to draw a continuation of a ridge line until it hits a roof face It doesn't really seem to flag up the point of intersection, It feels like I'm just hovering round hoping for the best.  Or am I doing something wrong? 

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I've been playing around a bit with the 3D polygon method and seem to be getting the hang of it, but snapping is still an issue. Alan - in your video you explicitly say 'snap to' points where the roof faces intersect - do you get a positive snap? I have my snaps all on but no sense that they're snapping there. I see also a post by Benson noting the lack of 3D snapping capability....





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Hi Mike

What we do to avoid any 3D snapping.  With the overlapping roof faces in top/plan view,  select the roof faces and use the modify/convert copy to lines command, and choose hidden line as the rendering option. You end up with a group of lines showing the outline of the roof plus the intersecting line between the roof faces.  Then you can trim the roof faces to this line. Easy.

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22 hours ago, mike-h said:

do you get a positive snap?

@mike-hHi, I do get a positive snap at the intersection of the 2 roof faces at the top intersection. It becomes a combination of smart edge and object. If you hover around the point with these settings you get the snap. Definatly when you hav only one corner and the long side you will guess it by zooming in but you get pretty close and with a texture of tile you dont see the gap, you get better at it and can get closer.



Edited by Alan Woodwell
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