How to add a section in the middle of a complex model

Hi, I’ve tried searching for answers but perhaps don’t understand the terms being used.

I have a model of a house for my daughter, 2 floors plus roof, at a fairly advanced stage now. Unfortunately to meet our Planning laws for floor areas, I now need to make the rooms at the back of the building slightly larger.

Effectively what I need to do is slice through the whole model (2 floors plus roof), move the two bits 300mm apart and fill the gap in.

Every method I try fails as either I am not selecting hidden objects (so I am just pulling the roof across and not the floors), or I am selecting unexpected bits of geometry that drag and distort parts of the interior of the model.

Any help greatly appreciated. It will be frustrating to have to re-draw completely at this stage.

Can you share the file so any of us can check how to solve it?

Sorry, the model is 46mb, and I am having trouble removing enough to fit in the upload limit. I will keep trying!

You could use a file transfer service like WeTransfer if the file size is too large.
It’s free and easy.

Hi Cappo,
Thank you, that is more practical. The link is: WeTransfer - Send Large Files & Share Photos Online - Up to 2GB Free
I’ve added a section XXX where I’d like to add the 300mm in to the model.

I’ve downloaded and had a quick look.

Your entire building is made of loose geometry. To stand a good chance of altering the structure at any point you should use groups or components as you work.

If I were you I’d attempt separating your model into groups and working on each part individually. That way when you drag a wall it wont accidentally drag and distort something else.

Hi Cappo,
Thanks for taking the time to look, but your comment is a bit dispiriting for me. Are you saying basically ‘bin it and start again’?

I haven’t looked at your model, but selecting the part that has to move (i would use the Lasso selection) and using the Move tool should do the trick.

Not at all.
You just need to spend a few hours tidying up what you’ve done.

I’d help more but I haven’t got enough time.

I’ve managed to separate out the roof and ground.

The building is a lot more complicated though as you have walls attached to furniture and it will take time delete out those bits not required.

2 - roof.skp (507.1 KB)
1 - ground.skp (3.2 MB)

Adding 30 cm to the model

Use Purge and your file go down from 46 MB to 6 MB

Basics of SketchUp at

Ok, that way’s much easier :rofl:

Hi Both,

Many thanks for your help. I am at work now, but will work through your solution later.


All of your tags are generated by items you have downloaded into the file. You definitely need to run purge to reduce file size. Consider grouping elements into tags like roof, walls, floor slabs and then group the walls together. Some people differentiate between exterior and interior walls. This approach will eliminate the issue of stick geometry. Take a look at teh AIA Cadd layering guideline, not that you need to use those but it will give you an isae haow to break up a model.