Help.. Trying to add a window into my wall

I cannot find this subtractive brush, that the video tutorial shows… I don’t even have a brush box tool inside my box details after I make the box, so it makes it impossiable to switch it to subtractive. I can make the wall and alt to make a new copy but neither copy has brush setting. I don’t understand what I’m supposed to do… Can someone help?

Which UE4 version do you use?

First of all try to reset all windows

After that, search for “Geometry -> Box” inside of Modes and place some boxes

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Go to the Detail Panel and set the box to Substractive (make sure you are selecting the box)

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Does this also remove the collision in the subtracted area?

yes it does - tested

Does this only work on additive brushes or is it possible to subtract from other meshes? Essentially I have a mesh that is an asteroid and I want to subtract from the asteroid to create an opening so I can make a cave inside the asteroid. The brush will subtract from other geometry brush objects but not my uasset static mesh asteroid. I’m in 4.12 (it must be 4.12 because it’s a specially modified source code version that will only work with 4.12). I would edit the assets in Blender but they are uassets from an unreal store package so I can’t export out of UE4.

Yes, it only works on brushes, not on static meshes.
If you want a hole in your Asteroid Mesh, you first have to export your Asset(as FBX or .obj) and import in Blender to edit it.
Here is the export option(sidenote: i convert the box brush into a static mesh - you can find the option inside the detail panel if you select your box brush):

I was under the impression it’s illegal to modify assets purchased from the Unreal Store using 3rd party software. Is that not true?

Found that here: https://publish.unrealengine.com/faq
I hope this could help you