Suspended Timber Floor Insulation

Suspended timber floor insulation is a method of insulating the space between the underside of a timber floor and the ground or void below. This type of insulation is commonly used to improve the energy efficiency of a building by reducing heat loss, increasing thermal comfort, and preventing dampness or moisture issues. It is particularly relevant in older period homes with suspended timber floors that may not have little to no insulation.

Insulating suspended timber floors in older homes can be a bit more challenging than insulating in newer constructions due to factors like limited space, irregularities in the floor structure, and the need to preserve the architectural integrity of the building.

Suspended Timber Floor

Hundreds of thousands of homes in Ireland have suspended timber floors. If your house is Georgian Style 1740-1830, Victorian Style 1830-1901 or Edwardian Style 1890-1918 then you most likely have suspended timber floors. Back in the day these were a great solution to overcome the difficulty of damp-proofing floors next to the ground. The major problem was that outside air flowed beneath the floors. Kiln dried floor boards were not in existence at the time so freshly cut timber flooring (Red Deal) was installed. This naturally shrank in the heated environment of a home leaving gaps between the floor boards. That’s not really an issue in summer but in Spring, Winter and Autumn this air is Baltic, greatly reducing the temperature in the room and making it draftee and uncomfortable.

Thankfully we have modern day solutions to eliminate this draft and insulate the floor. It’s a bit counter-intuitive but we must maintain outside air beneath the floor to ensure the floor joists don’t rot and also to eliminate the build-up of mould and condensation. The solution to insulating a suspended timber floor is three fold:
1. Vapour Control Layer
2. Insulation
3. Airtight Membrane


Insulating a Suspended Timber Floor in Ranelagh, Dublin 6

On our recent insulation project in Ranleagh, Dublin 6 we started by removing the skirting boards followed by slowly and carefully removing the original Red Deal floorboards, one board at a time. Each board was marked with numbers so it could be placed back in the same order as they were originally laid. The boards were inspected for any damage, rot, woodworm etc  and were then stored in a dry room at he same temperature of the room we had uplifted them from.

Once all boards were up-lifted and stored we then inspected the floor joists and wall plates for damage, woodworm, rot etc. We discovered that 3 joists needed to be replaced. After replacing the rotten joists we applied preservative as appropriate to the joist system.

We could then get started on insulation. To stop any moisture ingress, we installed a vapor barrier between the joists creating a pocket for the wool insulation to sit into.

We then installed Rock Wool throughout and sealed the floor with a breathable airtight membrane. This specialist membrane is breathable which prevents any condensation.

The original floors were then reinstalled board by board. Unfortunately, some boards were not salvageable and were replaced with re-salvaged Red Deal boards. The original skirting boards were re-installed and the floors were sanded, stain and varnished.

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