Okay so this is my model: And here is an example of one texture and its uv's (edges are not visible, but you can see what is happening): The plaster parts are uv'd like this (filling the whole uvmap). The another textures uv's are also filling the whole uvmap or almost the whole.
What I think Kristof is saying is you should use a multi sub object. This map channel thing will get expensive quick. Not to mention you'll have to remember which map channel holds which UVs for the house. I'm currently doing that and it's a pain. One map channel for the main texture, one for the Light Map, and maybe a…