Monday, July 21, 2008

Inconsistencies in Roofs

In Revit, we enter sketch mode to do a lot of operations, and is the way we interact with Revit to input the "geometry" parameter. Most of these operations involve sketching on a workplane and then Revit takes that geometric input and builds something with it for you, such as a wall elevation profile, a floor or a roof (by footprint).

Floor slabs grow downwards, so for example if your sketch is located at elevation 10'-0" on Level 2 and you use a 12" floor, the bottom of the floor will be at elevation 9'-0". A Roof by footprint behaves just the opposite and grows upwards.

Now this all makes sense (or not), but I have a problem with inconsistensies between how you build your roof. If you use a Roof by extrusion, it grows downwards instead. See the example below.

Now we don't typically use roofs by extrusion for flat roofs, but this was just to illustrate a point. I would rather come up with one rule and stick to it, such as see roofs by extrusion to consistently grow upwards like their footprint counterparts. You can argue that when sketching by extrusion, you know where the top of your roof is, however this seems to be a topic that can be argued from both sides. At least now you know the difference between the two modes!

You can also take a look at THIS POST for further discussion and a poll about the topic.



Anonymous said...


Nice Blog with good info.

Why don't you put my Newsletter on your links. I write the Revit 2009 books + wrote the CADALYST AEC column for 14 years. I also have 6 book on ADT, but use Revit in my office -- HEGRA Architects

I am the only AEC Industry Analyst who is a practicing Architect.

Ed Goldberg AIA, NCARB
Ed's Independent Voice

Dave Baldacchino said...

Hi Ed, thanks for your kind words!

I'm very familiar with your newsletter and am a subscriber. I added a link to the "Other Sites that I follow" list.

coreed said...

its dosen't make sense.
in the real world physical foot prints are from the level down and extrusions are fron the level up
(ha ha ha) :)

Anonymous said...

If we see your post from one angle then its really fruitful information but we we start thinking from other angle your provided information does not make sense. But its true as it is written in your post that if we use a roof by extrusion then it grows downwards instead....

Anyhow... nice effort to explain inconsistencies in roofs.

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