Old Houses and Five Sided Boxes

In the winter, air comes in through the bottom of your house and exits through the top. If you put a top hat on the house, that effectively stops most of the air flow without capping the bottom.  If you just cap the bottom, that also effectively stops the air flow. This is the five sided box idea. Five sided boxes (one side left unsealed) work nearly as well as six sided boxes (all sides sealed). What this means for your home, in practice, is that closing and insulating your crawl space has significant impact even if you have a very leaky attic.  Conversely, if you air seal and insulate your attic but you have a very leaky crawl space or basement, you will still see significant energy efficiency and comfort benefits.