Insulate under the ground floor#
As a very rough figure, 10% of the heat loss for an uninsulated building is through the flooring, but because people come into contact with the floor, it has a bigger effect on thermal comfort. Just providing warmer surface coverings like carpets can improve thermal comfort and retain a little more heat.
Although it’s easy to find vendors who are willing to put non-breatheable insulation under suspended timber floors, conservation architects tell us this risks condensation and damp. They particularly recommend natural materials - either hemp batting hung in nets under the joists or breatheable boards lain on runners attached to the joists. If you don’t have access from under the floor this means removing some of the floorboards temporarily.
Concrete and other floors that can’t be lifted are either insulated over the top, creating a step up, or when the concrete needs replaced. Solid floors generally lose less heat than suspended ones.