How does it make sense?
Um...
Well our house is not insulated at all and has a reinforced concrete frame and roof...
Over the winter the whole structure cools down and it is difficult to get it really warm.
The upstairs bedrooms in particular remain cold - I calculated that the roof above our bedroom weighs ~50 tonnes and would take about 25KW to heat up from an overnight ambient temperature of say 12°C to something more comfortable...
So by moving downstairs for the winter we only have to heat one floor and the basement (which stays fairly constant throughout the year) and don't have so much of a cold roof problem.
After all, I suspect that gas will not be cheaper this year than last...