It would have little to do with spacing if your entire building is one mesh, there’s just not enough room on the UVW space for all the information you’re trying to bake. Read through this:
http://www.worldofleveldesign.com/categories/udk/udk-lightmaps-01-basics-and-important-principles-for-creating-using-lightmaps.php
It’ll help you understand your problem and will allow you to easily see whats going wrong. It’s a simple problem with an easy solution.