I advise you to install rigid foam insulation on the interior of your walls. (greenbuildingadvisor.com)
The house has a full basement; I challenge anyone to find an inexpensive way to dig under the concrete slab and install rigid foam insulation. (dotearth.blogs.nytimes.com)
Its walls are constructed from prefabricated panels of rigid foam insulation sandwiched between sheets of oriented strand board (called «SIPs») and fitted with high - performance casement windows to create a tightly sealed envelope. (thetyee.ca)