We just bought a 100+ year old house and have started the renovations. We have heard there are some concerns about insulating an old house too tightly. What is your advice about insulating an old victorian/transitional house. Could we use spray foam insulation to seal the roof after the new roof is put on. We needed a whole new roof and unfortunately our budget dictatres fiberglass shingle instead of the original slate. Should we do the same to spray in the insulation in the exterior walls?