Unwanted diagonal lines on my drawings

When working on a project, I often get unwanted diagonal lines littering my drawing, point to point. How do I prevent this.

Generally that happens when the rectangles get deformed such that the edges do not lie in the same plane. In order to keep the faces, SketchUp creates the triangles. How are you modifying the model when this occurs?

1 Like

Thanks for replying Dave. All I have been able to do is to erase the lines. Unfortunately, that does not solve the problem, only the temporary situation. As soon as I start drawing again, the problem returns. At this time I can only restart the drawing and cross my fingers.


It is likely that the edges of the wall are slightly off plane, and this causes SketchUp to triangulate the faces when you edit. Do you have length snapping turned on? That can lead to small errors - it doesn’t snap to a grid as many noobs expect.

If you share the skp file we can take a look.

1 Like

Hi Steve,

FYI, In the case of this drawing, I copied it from the file I am working with for the project (so that I would not ruin it if we needed to test something) and pasted it on a new drawing. I hid the roof planes to see if any lines had appeared in the transfer, they did not. When I undid the hidden planes, what you see appeared.

I closed without saving, reopened and they were gone.

I would be pleased to share the file with you. How do I do so

Doug (Mountain Man)


When typing a reply in the forum, drag the skp file into the reply window.

Here is a cop of the skp file for you to review.


(Attachment 10 mackie 3.skb is missing)

Wait until the attachment has finished uploading until clicking Reply.

1 Like

10 mackie 3.skp (582.2 KB)

This should be the full and correct file.


As already mentioned, you have length snapping enabled. This is known to cause these tiny errors. Turn it off and save your template with it off. Window/Model Info/Units
Usually the best way to fix this is to start from scratch or you just chase the errors.
You should also look into using and understanding groups and components. As your model is all just one mass of raw geometry small errors can effect the whole model. Bump one corner and several rooms are out of alignment.

1 Like

Things in your model are ever so slightly out of alignment. See, for instance, the corners of the floor in this room:

I switched the Units to Decimal and increased the shown accuracy.
The errors are probably due to Length Snapping being on and that your house is a bunch of loose geometry where moving something can lead to attached other things moving. Creating groups and components of your house parts while modelling helps to keep things manageable. You have tried to repair the errors by redrawing things that has led to partly duplicate faces that are slightly misaligned.


OK, I think I understand what you are saying. I try to be accurate by locking to a direction as well as holding the curser at the start or finish point to be sure that I am at the proper start/finish point. Obviously that is not working. I guess I need to insure that I do not have length snapping on. How do I do that?

Turn it off in Model Info>Units. Do that in your model but also do that in a new, blank file and save it as your default template.

I have turned it off in my on going project and will make that part of my ongoing template.

Thank you for your time and attention.

Have a great holiday,

Douglas Barnard

1 Like

You have just raw geometry, try to work with groups or components, if you have elements that are repeated on your project it’s very helpful, in case you want to make some changes, you just have to make it on one instance and the others will be affected as well. If they’re just single elements try to make them groups, for example the floor or walls can be just single group and a truss can be a component. This workflow helps you to have more control over your project, and will make easier if you use tags, or the outliner, you can just hide elements you don’t need to be shown while working on something else, with raw geometry everything will just be one element and it’s gonna be hard to hide or tag separated elements.

Hi Douglas. Another useful way of checking if your lines are orthogonal (ie, straight and perpendicular to each other) is to go into Styles and select ‘By color’ and this will colour all your lines red, green or blue depending on the axis (X, Y or Z). I’ve attached a pdf explaining this.

Styles-axis colours.pdf (481.7 KB)

This is just a general guide. It can still introduce small errors. Best practice is locking the inference with the arrow keys, don’t forget the down arrow key.

@RLGL’s advice is key to success in SketchUp: learn to use its inference engine constantly and effectively. The majority of small errors result from failing to follow this best practice.

A close second is leaving length snapping turned on and not typing in lengths that must be exact.