How to make blender stop treating a non-solid object as solid?

See screenshots below, I’m just trying to put a hole in the pink object which is just a simple set of five faces of a bay window.

But blender is for some reason determined to treat the object as solid even though it clearly is not, and attempts to add faces in:


How do i stop this and make blender just carve out the object that exists without doing its own completely random thing?

Take special note of the “Warning” bit.

No idea what it means, do you know whats wrong or not? I’f i’m not meant to use boolean modifier what should I use to make the hole in it?

Non-solid bad. Solid good. Make good. Or cut other way. Edit mode lots of tools.

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No. What I’m saying is what that very documentation that you have “no idea what it means” is saying. You’re not guaranteed proper results with non-manifold meshes. It also explains what manifold and non-manifold are without resorting to gems like “3D (ie cubelike/closed without openings)”. Doesn’t mean you can’t use the modifier with such geometry, only means that you’re not guaranteed proper results.

You’re all over the place. The docs are too difficult. The small words are “obtuse”. And you’re being rude to boot.

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Hi, for a simple object like yours i would do it in edit mode like this:

Hi, i just used plane with cube and it works fine here:

Yet, add two loopcuts and drag the edges down a little bit, and the hole will turn into an extrusion. It can work or it can fail, depending on the input. OTOH, add a Solidify before the Boolean, and the cut is back, move edges or no.