Retrofitting older buildings with floor insulation where there is no damp proof course or membrane

2 April 2019 Kingspan Insulation UK
Old house

When carrying out refurbishment works, there may be a desire to improve the thermal performance of the fabric of the building at the same time, and in some cases, it may be necessary to improve the insulation at the same time to meet regulations.

However the age of the building, and the method of construction used, especially when considering floor insulation, must be taken into account when deciding what could or should be done. If a suspended timber floor is in place, then this can be insulated as shown in our how to video ‘How to install Kooltherm K103 Floorboard from above joists in a suspended timber floor’.

For a solid floor, specific attention should be paid to the construction of the wall, and especially considering if a damp proof course (DPC) is present, as this might not be the case in older buildings. If a damp proof course is present, then a complete damp proof membrane (DPM) should be installed to protect against moisture from the ground. The insulation is usually fitted above the damp proof membrane with a separation layer above the insulation.

When an existing floor is improved, or where a new floor is constructed adjacent to existing walls or floors (e.g. where a dwelling is extended), care should be taken to link the new floor DPM to the existing building DPM and to the wall DPC.

If there is no damp proof course present, which may apply in some older structures, then it may not be appropriate to install a damp proof membrane without also introducing a DPC, as otherwise this might concentrate moisture at the wall footings. Where it is not possible to introduce a DPC, efforts should be made to address the outside conditions such as ground levels and drainage in order to mitigate water ingress and moisture problems. The expert advice of an appropriate retrofit specialist should be sought when considering options in such situations.

NB: Kingspan Kooltherm K103 Floorboard, Kingspan Thermafloor TF70 and Kingspan OPTIM-R must be installed above the DPM, and cannot be installed into a solid floor without adequate protection from moisture penetration. Kingspan GreenGuard can be installed into a floor either above or below the DPM, and where deemed appropriate, onto a floor without a DPM.

For more information about the different types of floor insulation available, please see our flooring application page.