Problem getting lines to close a surface

I’m working on the roof(s) of my vacation cottage, specifically closing up the gable end.
It seems to me that if I draw a line from one corner, to the ridge, down to the other corner, and back to the first corner, I must have created a closed surface (one that I can pull out for the entire length of the roof). Nope.

If I use the same method for creating a triangle in free-space, SketchUp does exactly what I want. But on the gable end, no such luck.

What am I missing?

Dave Brown

Can you upload the model to the forum, to make it easier for someone to help you? If it isn’t over about 15MB, just drag the .skp file into your post.

(If as your profile suggests, you are using SU Shop, open the three-line menu, and Download your model to your computer first, then drag it into your post.)

The most likely reason is you are not hitting the endpoint when you finish the triangle.
But as @john_mcclenahan says, we need to see the model to check.

That’s what I thought too. At the intersection of the roof line and the fascia and the building, the lines get pretty busy. I’ve tried again but something weird is happening that I don’t yet understand. I see this as an opportunity to better understand some of the subtleties of SketchUp.

Thank you for being willing to look at my model and show me the error of my ways!

1 Like

Did you mean to upload something?

Grovehurst Roof Plan - Rev B.skp (4.0 MB)
I’m trying to add the last part of my cottage roof. Following Aaron’s instructional video, I added the lines showing the direction of the roofline. That’s where I got stuck closing the geometry.

The fundamental problem is that the corners of the candidate triangle are not in the same plane. You can see that in this image: the green coordinates are not the same. The lower left one, in particular. You need to pay closer attention to inference snaps while drawing.

Edit: actually, there’s more of a mess going on there than I saw at first:

Screen Shot 2021-02-10 at 2.23.12 PM

First things first, I’d recommend unchecking “enable length snapping” >Window>model info> units.
It’s likely causing these small errors, or at least helping you create them.


Without being rude my first recommendation would be throw the model away and start again. Unfortunately it is a rats nest of loose , stray and hidden geometry that is mostly out of alignment and on mixed layers/tags.
If you look at this gif you can see all the hidden geometry that will drive you to insanity.

I would start from Scratch. Turn off length snapping as mentioned above and set that, with any other style changes you might want, as your template so it is always off.
Then draw your model using mostly the rectangle tool so things tend to stay flat and ‘group early and often’. Meaning make groups and components of everything as you go so things don’t stick together and effect everything around them. 'accidentally shift one corner vertex and the whole house is suddenly out of whack.
Leave Untagged as the active Tag and only assign a tag to groups or components, never loose geometry. If you explode a group/component that you have already tagged reset that exploded geometry to Untagged.
Work in monochrome mode so you can keep the face orientation corrected, all white faces should be visible, blue are back faces and should be contained within shapes, unless it is a single skin. But then nothing in a house would normally be a single skin as it has no thickness.

Keep the original model if you want as a reference, but have it open as a second instance of Sketchup and build the new one in a fresh clean instance.


One thing that is not always mentioned in the use of Groups is that it is much easier to throw just that part of your model away and start over. In regular projects I often replace groups for the roof or foundation wholesale. I most often KEEP the group or component but replace a lot of the geometry that is in it. Not often because it is wrong but changes in the design mean it is easier to do a portion of the model over rather than patch-in the changes. And with separate groups and components for the roof, walls, floor etc. you can rework that part regardless of the condition of the rest of the model.