When an existing dwelling has a suspended timber joist ground floor, the best way to upgrade the thermal performance of the floor is to install flexible insulation between the joists.
To do this the floor boards will need to be taken up, so this process is best carried out when a dwelling is empty or one room at a time with all the furniture and floor coverings removed.
The first element to install is an insumate tray which is stapled to the existing floor joists. Once this is installed select an insulation depth that matches the depth of the floor joists and install it between all joists, ensuring all voids between walls and joists are filled.
Once insulation is installed, fix the floorboards back down and ensure gaps between floorboards and skirting boards are filled with silicone sealent for air tightness.
If there are any electrical cables within the floor void ensure they are either tacked to the side of the joists or if they run perpendicular to the joists, are adequately protected and not encapsulated by the insulation.
Ensure void below floor joists is clear and not filled with any insulation and make sure any ventilation to the void is not obstructed by the new insulation.
If gaps between walls and floor joists are less than 25mm then fill with expanding foam.
Where any service pipes or electrical cables pass through the joists, mark the top of the joist with the location and depth so when the floorboards are replaced fixings do not cause any damage.