I have a 1600s or so scottish cottage, that's lacking in insulation. It's some 20m*5m, with a suspended wooden floor, with no insulation underneath. The temperature below the suspended floor is essentially the average house temp. During other works, the path (20*1m) along one long side of the house has been dug up. Is there any point at all in putting down 2-5cm of rigid insulation under sand blinding, then membrane, and gravel, instead of just the gravel and membrane?
How would I go about calculating the extra insulation effect?