How do you model sloped roof framing? Its not as straight forward as you might think!
There appears to be a number of different approaches to modelling sloped structural framing. Here I thought we’d take a look at the two best options to suit most situations.
I would strongly recommend playing around with your options for modelling sloped structural framing. I don’t believe there is a one method suits all approach to this topic. Your approach will be largely dictated by the level of complexity of the roof. If I had to give one golden nugget of advice regarding modelling sloped structural framing (or anything else for that matter), it would be THINK BEFORE YOU MODEL.
Firstly I assume you have modelled your columns. Probably best to try these methods out on a practice model first.
Option 1 – Modelling on a Reference Plane
This option would only really suit modelling of structural framing to a single sloped roof. Its a relatively straight forward approach, simple to model, but on further investigation this approach seems to be fundamentally flawed (at least Revit thinks so!!).
Here we go…
- Enter a section or elevation view which will be suitable to draw your reference plane at the desired pitch. Draw your reference plane at the required level, name the reference plane (see below image).
- Go back into the roof datum level view, assign the newly created reference plane as your current work plane(see below image). Note in this image I have added the reference plane tools to my QAT (Quick Access Toolbar) the ‘Set Work Plane’ tool is normally on your ribbon under the ‘Home’ tab, on the ‘Work Plane’ panel.
- Ensure 3D snapping is off as you want to draw on the plane and not be snapping to points at varying heights. Draw in all your required beams. I find the ‘Beam on Grids’ tool works best for this (see below image). (Note: If necessary follow up with secondary members spanning between primary members using the beam system tool, ensuring you use the sketch boundary>pick supports option to ensure your beam system slopes with the adjacent primary members)..
- Select your members that run horizontally and adjust the Constraints>Orientation property from ‘Normal’ to ‘Horizontal’ (see below image) this will ensure the horizontal (non sloped) members are orientated correctly. I would also select all roof members and set the Structural>Stick Symbol Location property to ‘Top of Geometry’ to ensure you steel views correctly in plan views.
Now, I believe that this should give you a correctly modelled roof that has the ability to be manipulated in terms of the pitch of the roof and the height of the steel. It seems I am wrong. Here is what happens if you move your reference plane vertically down by 1m.
In my opinion when modelled this way, the beams on grid lines should remain locked to the intersection of the reference plane and the grid line. And it seems that is what is meant to happen. If you drag your grid lines with the beams that did not move correctly (in this case GLs A, B, & C) Revit jumps into action and realigns the beams as they should be. But, we can’t go dragging GLs around in a live project, you could cause yourself no end of troubles! Please fix this bug Mr Autodesk!
Another point to make is that your roof steel will ‘break’ if you try to adjust the pitch of the reference plane. So don’t do that either.
In conclusion I think this option is quick to model and provides you with the desired end result. But, you need to be sure that the pitch and level of the roof steel is not going to change.
…onto option 2.
Option 2 – The only really viable option
I reckon that as Revit is a 3D application that it makes sense to adopt some principles of 3D modelling and stop trying to model like a 2d drafter might (as in the option above).
Firstly I assume as above you have modelled your columns and have either a reference plane or roof (or whatever) to which your columns are attached.
- Head over to any 3D view, ensure you set your work plane to the relevant roof datum level.
- Activate your beam tool, check the tick box for ‘3D snapping’ and start snapping your beams to the tops of your columns (for some reason I cannot get the chain function to work when doing this?!?, so you have to snap the start and end of every beam).
- You can still use the beam system tool as above to model all of the secondary members.
- One point to highlight, which I will cover in my next post is that the beams will not be at the same level as the reference plane (or whatever your columns are attached to) unless your columns ‘Constraints>Attachment Justification at Top’ properties are set to ‘Intersect Column Midline’ (and you most likely won’t want to use this setting). I will show you in the next post how to offset your beams to maintain the correct level and what the different options are for your column justification.
Now I would have thought that this method of modelling the roof steel would result in a fully flexible beast. It should give me the ability to change the height and pitch without too much additional input from myself. WRONG!
If you try and adjust the height of your reference plane you will be surprised to find your steel framing is quite happy to stay where it was modelled and not follow the top of the columns and reference plane (this will mostly likely lead to your standard ‘elements cannot remain joined warnings’).
This can be rectified by changing a couple of the properties of your newly modelled roof members.
If you select all of your roof members and change the ‘Structural>Start Attachment Type’ and ‘Structural>End Attachment Type’ properties from ‘End Elevation to ‘Distance’ (see below image).
You will now notice some additional properties become available.
‘Start Attachment Distance’, ‘End of Referenced Column’, ‘End Attachment Distance’ & another instance of ‘End of Referenced Column’ (I assume the two instances of the same property refer to the start and end conditions of each member).
Your start and end attachment distance properties need to be set to ‘0′(zero). Your ‘End of Referenced Column’ properties need to be set to top (see below image).
Now, you have roof steelwork that will adjust should the height or pitch of your roof change (although if the pitch changes you will need to revisit the offsets of the roof members I will be covering this in the next post).
And there we have it folks. It was a short (relatively) and sharp outline of a couple of methods for sloped (roof) structural framing. If you spot any mistakes in the above, they are in fact deliberate and I was just seeing if you were concentrating!
Happy Reviting chaps!