Weird squares everywhere

So in unity I have some weird squares on surfaces of certain objects, which are buildings represented by planes:

I don't know what causes it, I tried changing some settings in lighting and material, but couldn't fix it. This only occurs with one object which is a few planes representing buildings temporarily. The lighting is baked (one directional light). Here's the screenshots of lighting and materials tab:

Does anyone know what could be the problem and how I can fix it? Ask for more information if needed. Thanks.

EDIT: The buildings were imported from blender.

• There is also another planes behind those visible in picture to stop the light passing as planes are single sided. So every single plane has a duplicate turned 180 degrees – Vadim Tatarnikov Feb 7 '16 at 12:01
• Don't do that. Set the rendering mode of the Mesh Renderer on each plane to Two Sided and remove the duplicates. – EvilTak Feb 7 '16 at 17:41
• I don't see where I can do so. I could write a shader to render both sides but then the light will still be penetrating the planes so there will be no shadows. – Vadim Tatarnikov Feb 7 '16 at 18:07
• my mistake, set the Cast Shadows variable on each Plane's Mesh Renderer to Two Sided. – EvilTak Feb 7 '16 at 18:10
• Ok so I set it to Two Sided but at the end of baking the squares still appear. Do you know if I need to tweak something in the lightmap? Because when I set my directional light from baked to realtime everything looks good without any weird shapes. Currently it's set to Baked. – Vadim Tatarnikov Feb 7 '16 at 18:32