I have a home in South Lake Tahoe. It was built in the early 1900s. The House is stone, with a slate roof and it has absoultely no insulation in it. We are winterizing the home so we can extend our use. The question I have is what is the best insulation to use in the roof? The walls have little space 1 1/2" - 2" for insulation. Is hard foam an option.