We have a 1970's bungalow with tongue and groove softwood floorboards. Plenty of space to get under the floor without taking up the boards. There is no underfloor insulation. We'd like to take up the carpet, sand the floorboards and put insulation between the joists under the floor. I've been told this will probably cause the floorboards to shrink and create gaps between them. Has anyone any experience or advice?