I had a handyman out estimating a painting job today and he felt the exterior wall of my bedroom (plaster on brick, no insulation, 1950 construction date) and noticed it was quite cold.
He suggested tacking up foam insulation board on the inside of the exterior bedroom walls, then drywalling over them and deepening the windowsills/reframing the radiator recesses. He claims that with a loss of only 1.5" of space on 2 walls there will be a huge improvement in comfort.
Researching this technique online it appears it's mostly used in basements and crawlspaces, and I see warnings about water/mildew, fire hazards, critter infestations and other nasty things. To top it off there's an existing hot water baseboard along all of these walls that would have to be moved or finished in some odd slightly-recessed way to make this idea work.
Is this a reasonable thing to be considering doing? Is it safe? Legal? Worth the trouble and expense? (Can 1" of insulation board even provide much R value?)