Weird lighting issues

Hi, i’ve been stuck with an issue for the past couple of days and cant seem to figure out a way to fix it.
My issue is shadows/lighting casting very weirdly in my meshes. I have tried changing up the lightmap, changing the lightmap resolution, rebuilding the mesh from scratch etc. The mesh is a big house built out of one block, not several (which should be preferred right? I might be wrong).
The issues are only around in the darker areas of the house, the bright parts look great.
I’ve even had an experienced (but rusty) maya user look at my mesh and clean it up, without any improvement.

http://puu.sh/gQHCP/88a075a864.jpg

http://puu.sh/gQAFa/d7ffbfc692.jpg

The problem is having a mesh that large in one piece. You would need extremely high lightmap resolution to get a reasonable lightmap for it, otherwise light will keep leaking to shadowed areas . So you need to split it into walls,floor and ceiling at least.

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Thanks for the quick answer Jacky, I had a slight assumption that was the issue but I also thought that stuff had to be built in one single mesh for the best performance.