Jump to content

Walls / Slabs / Windows and Doors

Recommended Posts

Hi guys, 


I'm trying to dive into the BIM modeling to create a file for a house for the first time. I would like some help to well address some construction connections in-between some elements.

For instance, I have a slab that is normally composed by a structural element with 17cm, then a screed with 10 cm for filling purposes and also underfloor heating and then the finishing that can varies in between 2 and 3 cm. Until now, no worries.

I have managed to create the desired connection in between the exterior wall exterior component and the slab with the offset values so that the isolation could descend to the total thickness of the slab.

Nonetheless I've encountered two problems.


1# If I have a different finish in between two rooms, how do I resolve this? For instance, in one room the finish layer as 3 cm made with 2cm of screed and 1cm for some tile, and the other room is simple 1cm of cork and 2 of wood pavement. Do I need to create two different slabs? One for each area?


2# Normally the wall that divide this two spaces in my case is made of brick and it's supposed to be constructed directly over the structural slab, so it means that in my case this wall should descend 13 cm to connect with the structural core of the slab.


Can any of you guys tell me if you know how to resolve some of this issues?


Thanks in advance, 


Link to comment

Hi Bruno,


1. We split the structural Slab object and the finishes Slab object onto two different layers. In fact we don't tend to model floor finishes, we usually just treat the screed as finished floor level and ignore the finishes. In your case some of your floors don't have a screed so ignoring finishes may not be the best approach.


So we tend to put a floor finishes Slab (usually just a screed) on the same layer as our main walls, and then we put the floor structure on a separate layer altogether. We don't auto-connect the slabs to the walls because we find the connections never persist. They're always getting broken because of moving walls or changing wall build ups.


So in answer to your question, yes you need at least two Slab styles. Personally I would use at least three: one for your structure on a separate layer and the others for everything you want to model above the structure (either on their own floor finishes layer or on the same layer as the main walls).


2. You can control these connections automatically by setting the bottom and top wall component bindings (under Wall Component Settings) + the slab component Edge Offset (under Slab Component Settings), and then auto-binding the slabs to the walls, but, again, we find the auto-binding approach breaks too often and slab edges don't remain where they're meant to. So what we do instead is to manually add the structural Slab object using the Polyline Mode and then edit the wall top and bottom bindings and offsets to suit (in your case you would set the brick component of your wall to bind to top of your slab). Depending on the complexity of conditions we may set the top and bottom wall components by Wall Style or we may do it for each wall manually (in practice a bit of both).


To set your levels you need to be using Stories. In each Story you can set any level you like. For instance, for your structural slab you would create a Level called Top of Slab and you'd would set the Elevation to -3 cm relative to the story (for your screed + tiles area). And, if you follow my advice, you'd also create a separate layer to go with it.


If you want all the floor finishes to be perfectly flush then you may decide to set your structural slabs at different levels to suit the finishes. But I imagine you're probably happy with 1-2 cm difference in finished floor levels between rooms, in which case you'd stick with one level for your structural Slab.

Edited by Christiaan
  • Like 3
Link to comment

Normally a structural slab flows over the whole Story.

Finish floors, and often the package beneath, vary between rooms.

So it is also less tedious and needs less slab styles.

And you can easily fill the finish floors into each room by paint bucket mode.


Just the door cut areas may need an extra floor rectangle.

Edited by zoomer
  • Like 2
Link to comment
  • 3 years later...
1 hour ago, Stéphane said:

How would you create vertical linear elements in floors, typically sound insulation for floating screed ? 


If I got the question right,

it should be the same problem as for studded Walls ?


Hatch ?

And hoping that size and location fits mostly ?

Link to comment

@Tom W., @zoomer, I mean everything that could be part of a floor but are vertical more than horizontal. For instance when you need to insulate your screed... See images below :


I was wondering how you would do it. 3D model it ? Or patch it directly in the layout ? Or is it just going too much into details and you would produce anyway a 2D detail ? 






  • Like 1
Link to comment
53 minutes ago, Stéphane said:

I was wondering how you would do it. 3D model it ? Or patch it directly in the layout ? Or is it just going too much into details and you would produce anyway a 2D detail ? 


You could use Slab objects for that too; if I was doing this I would create a Slab object for each length of wall, pretty as they'd exist in the real world. Then manually adjust your screed Slab to suit or add offsets to the edges. But I wouldn't bother, leave that for 1:5/1:10 details*. The only reason I can think to include this level of detail in the model is if you needed it for 3D thermal modelling reasons.


* Work Drawings Handbook by Keith Styles and Andrew Bichard is worth a read on this topic.

Edited by Christiaan
  • Like 2
Link to comment
  • 7 months later...


I'm wondering what workflow will allow me a thickened slab that would be bound to the walls? The hope is that as I develop the design, and move the walls, the slab edge will stretch with them.


I drew a a concrete slab on grade w/gravel (from library) and bound it to the walls above. It does what I need, and stretches as the walls move.


I tried binding a second perimeter of concrete walls below the slab, but can't bind it to the same slab.

I tried  adding an EAP to the slab. (thanks @Tom W. didn't know I could do that! learnt something new)  This looks great in sections, but does not 'stick' to the slab - when the wall moves, the slab moves with it, but the EAP stays in the original location.


Is there a trick I'm not using?





Link to comment

Hi @taliho no you're correct despite appearing to become a homogeneous part of the Slab the EAP is not really connected to it + needs to be moved separately unfortunately. Right-click or double-click on the Slab + select 'Edit Modifiers' to access the EAP + in turn the EAP's path in order to move that to match the reshaped Slab. Bit of a faff but for me at least doesn't take away from the fact that 'Add 3D Object To Slab...' is a really useful + versatile feature - I wish we could do the same with Walls + Roofs!


I tend to design the Slab/Wall interface anticipating the toe detail or upstand or whatever it is on the slab but don't actually add it until later on when things are a bit more fixed

Link to comment
9 hours ago, taliho said:

I'm wondering what workflow will allow me a thickened slab that would be bound to the walls? The hope is that as I develop the design, and move the walls, the slab edge will stretch with them.


That is exactly how Slabs, bound to (a closed set of) Walls are meant to work.

If you move the Walls, the overall Slab will follow.

But you can have also control over each individual Slab Component. Like

Floor Package stops at Walls inner Side, While Structural Slab extends to

the outer side of the Wall.


Why do you want to bind a single Slab to 2 Sets of Walls ?

As the 2 Wall Sets, above and below, aren't linked to each other either.

(The lower Walls are kind of foundation walls ?)


I always bind my Slabs to the Walls above.

(So I can look inside each story from above)

This way, even if you have 50 Stories, you can select all related Walls

in Top Plan for all Stories - move them - and all Stories Slabs will follow.

Link to comment

If it is a Foundation,

it just draw it with Walls, on their own Layer.

I see them as a separate Story below.


OK the Foundation Walls will not automatically follow changes

of the upper Wall, like the Slab does. But you can easily

select and move them together with the upper Walls or just

move them separately later.

Link to comment

Thanks to @Tom W.and @zoomer -


My work is mostly small residential projects, many of them slab on grade foundation. Typically I do not need a raft - the concrete is poured into a perimeter trench with rebar. Up til now I was adding the footing/thickened edge as a 2D line on each individual section, (I create a symbol for it) and was hoping that I can model it as part of the building to save time (and work more accurately in clip cube). I have been fortunate to work in mostly flat-land projects, so haven't had to deal with sloped terrain at all, and I was hoping its an easy flow.


So I learnt that I can do an EAP addition - I should just do it at one of the later stages of design.  That would make my wall sections, using attributes of original objects, look really good right at the first cut. Can the slab perimeter be used as the path? (without drawing a polygon over it). 


I also tried adding a 15" thick CIP wall below the slab on the same design layer (can't bind it to the slab...) But even if I select both first level framed wall and CIP footing wall and drag to enlarge the room, only one of the walls moves. I don't work in Stories - is that the difference?


Thanks again for your time responding to this - on a Saturday....



Edited by taliho
Link to comment
57 minutes ago, taliho said:

But even if I select both first level framed wall and CIP footing wall and drag to enlarge the room, only one of the walls moves.


That should not happen,

as long as the Slab is still healthy bound to a Set of Walls.


If you had a multi Story Building, each Story's Slab bound to its outer Walls,

if you drag all outer south Walls, alls Story's Slab will follow.



Maybe you can check in OIP if the Slab is still bound to Walls or just says Bounding : Manual

As it is quite easy to lose a Slab's Wall bounding when manipulating Walls.

If you move ALL bounding Walls at a time, without also moving the Slab, the Slab will stay at

its previous position and such things ....


Or re-bounding the Slab to either the Walls above or below the Slab.

That is why I create a separate Story (at least Layer) for Foundation Walls.

You can draw walls over each other on a single Layer, but you will get problems

with Wall Connections very easily.

(And AFAIK un-connecting Walls or similar may lead to Slabs losing their bounding)

Link to comment

Hi @taliho I'm not completely sure the construction you're describing + the ways you've been going about drawing it (post some screenshots...?) but for a concrete strip foundation with concrete piers on top I would use two walls like @zoomer described above, one above the other. Then bind the slab on grade to the pier walls:



If you move the pier walls the slab will move with them but in my example I have included perimeter insulation which is an EAP added to the insulation component using 'Add 3D Object to Slab...'. As described above, when you reshape the slab this EAP needs to be reshaped separately by editing the modifier.


Again as Zoomer said the strip foundation walls (footings) you'd need to move separately as well.


Or perhaps this is the detail you want:


This time the pier wall has two components, the inner one with a negative top offset, but it is still auto-bounded to the slab. Not sure why the footing is no longer merged with the foundation wall but for me I probably wouldn't mind this as in reality they are two separate objects that would be constructed separately.

  • Like 3
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...