Drawing a line doesn't split an object?

I’m trying to separate a ceiling plane from the walls of my Sketchup model, but no matter how many times I trace the lines I can’t select just the ceiling. Any ideas why this is happening?

Here’s a look at what I mean. Notice that the entire top plane is selected even though the ceilings of the rooms are separated from the walls by lines. I would like to select just the ceiling and not the tops of the walls.

Thanks for your help!

Hi @ashleyflamion91, I can help you. Is it possible for you to upload your SketchUp file, to help you more quickly?

The SKP would be very helpful…
Meanwhile ensure that your Model Info > Units is NOT set to enable length snapping, this can make your drawn line stop short.
Also ensure that you are in the same context as the face and other edges - i.e. edit its component/group, then draw…
Also try select everything in that context and use intersect [context-menu item] to try and force the split.

This can also happen if the tops of the dividing walls are not exactly in the same plane as the tops of the outer walls. When off by just a tiny amount, they can “bleed” through and appear to cut the larger face when they actually do not. But it isn’t possible to diagnose that situation without examining the model. Can you share it with us?

Here’s what I’ve got. I haven’t checked the length snapping yet, I’ll have to look into that. I haven’t made any of the walls or ceilings into groups or components, so that shouldn’t be the issue. I checked to make sure it wasn’t an alignment issue before I posted the thread, but there are so many lines that I totally could have missed something. Please do let me know if you guys find something, this has already been so helpful. Thanks!

Hm, I keep trying to upload my model and it keeps disappearing :weary:
Okay, I’ll try it as a link then:
Link to the skp in my dropbox

Another update: doesn’t look like it’s the length snapping issue and intersect didn’t fix it. So, we’re back at square one I think.

Almost all of your model is loose geometry.

Make each separate wall into a component or group, or at the least, make all the geometry except the ceiling into a single large component.

It was then easy to select and cut to clipboard the lower part of the ceiling, as one face.

Paste it somewhere else, then make it into a component.

You have other parts of the ceiling hidden, so if you were to put it back where it came from, the geometry would merge with the hidden ceiling parts.

But when I pasted the ceiling back, it clearly isn’t all in one plane - as you say, Intersect Faces doesn’t work to split the ceiling into separate parts for each room. Using move up on blue axis on the Face selected from the ceiling leaves a lot of loose points and stray lines below it.

I’d be inclined to delete the ceiling pieces, then draw a plane on top of the walls, then trace round the walls using On Face inference to get the rectangles or lines in the plane of the tops of the walls.

I’ve started this, as an example, to get the three bottom left faces in the ceiling - two rectangular, and one L-shaped, shown selected and slightly darker shaded in this image:


Haven’t the time to complete the process, but I hope you get the idea.

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