Our house was insulated with blow in cavity wall insulation when it was being built about 40 years ago. I have noticed that the house has gotten a lot colder in the last few years and i am wondering if this insulation could have deteriorated in the walls, and if so can it be redone in the same way now. I do not want to dry line the walls inside. Our windows have been replaced, so we think the walls are our problem. Originally this insulation came with a 25 year guarantee. I would be grateful for any help on this. Thanks.