instead of separating every uv face, stitch more of the UV faces into fewer, larger islands so you can have less space wasted on padding. pad in between objects to avoid bleeding, but don’t pad around the edges of the lightmap, because that padding will be automatically generated. instead of treating the whole building as a single object, separate it into many different objects, so they each get their own lightmap. also you should snap lightmap UVs to the nearest pixel to avoid baking problems.