No I mean not tender for private contracts to do this. Actually do this in a nationalised way.
Setup a department, NIS (the afore mentioned National Insulation Service), with the motto warmth at the point of use, build a workforce that goes town by town coldest to hottest parts of the country and adds the required missing insulation to however many homes need it starting with low income homes.
Everyone is so keen on nationalising everything so why not kickstart this and do some good. I say the same thing about home building. Set up a government home building project entirely run by government employees funded by the state. I can understand how there would be NIMBY protectionism against that (can't build that here you'll lower the value of my mansion) but who would argue against insulation?