One of the most effective ways of dealing with existing uninsulated frame walls is to blow cellulose into the wall cavities. This is a popular and time-proven method of retrofitting insulation and is a mainstay of low-cost weatherization programs. It is popular for good reason—it works very well. Dense packing walls typically results in remarkable performance. It is the dense packing of unvented cathedral ceilings or unvented flat roofs that is the problem. The job can be done from either inside or outside of the house.