Whenever possible, I persuade my customers to use insulating concrete forms (ICFs) for their foundations — particularly if they intend to use the basement as a finished living space. I like ICFs because they can be assembled by the on-site crew, there are no heavy forms to haul and set, and rebar is easy to place. ICFs also have a high built-in insulating value and, unlike retrofitted rigid foam board, they align with the framing above. Membrane System As with a conventional basement foundation, ICFs must be waterproofed below grade. Because of the joints between the blocks, foam forms alone won't prevent water penetration. In the past, I've used Tuff 'n' Dri, a dealerapplied spray-on elastomeric coating that cures very quickly.