I'm freezing and cheap. I am trying to figure out what to do with the external walls upstairs. Like most older houses, I have no insulation. Some of my friends have been having insulation blown in through holes (either external or internal) - either cellulose or foam. I have done research and foam is unproven at this time (they need thermal imaging to identify whether the cavity has indeed been filled, plus with rapid expansion it can crack your walls - or worse) and cellulose settles to the bottom with time.

I want to avoid ripping the plaster/lathe down. I would also like to avoid putting insulation on the interior and refinishing.

So - a thought came about using siding and hard foam insulation panels on the exterior.

Any suggestions or experience in this area? Comments appreciated.

Thanks!