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feature
floors, walls, ceilings & acoustics JN228
air from rising from the vented airspace below the floor joists from rising up through the insulation zone and into the room above. The membrane needs to be draped up and over the joists
to create a cradle to support the insulation material and it is sufficiently robust to do this throughout the service life of the installation, with no risk of bending. The breathable membrane is secured in place over the joists with galvanised staples that are at least 10mm wide and 8mm deep. Staples should be used every 10-15cm along the bottom edge of the joist, with a timber batten installed over the top (along the bottom end of the joist) for maximum long-term strength and durability of the installation. The wall will need to be primed first with an airtight tape surface primer before the tape is applied. The overlaps of each length of the membrane should be taped and then the perimeter edge of the membrane should be sealed to the walls. As the membrane supporting the insulation is draped up and over the joists, a project will need enough membrane to cover 1.5x the square meterage of the floor.
A suitable insulation material for use in suspended timber floors is Gramitherm, a natural, breathable and high-performance insulation with hygroscopic properties that allows moisture to be released gradually. This helps to offset the risk of condensation within the insulation layer.
Gramitherm can be installed tightly between the joists and cut
to size easily on site. The high density of the material offsets any risk of slumping over time. This stability maintains its thermal performance, ensuring long-lasting insulation effectiveness.
Another alternative is wood fibre insulation which also offers a dense material with hygroscopic properties. It is important to protect any fibrous insulation with membranes, just like adding a Gore-Tex jacket over a woolly jumper. In this way, the project achieves its objectives without creating issues such as ‘wind-washing’ and secondary issues of damp, condensation and mould. Once the natural, breathable insulation has been installed, an airtightness membrane is laid over the top, which is then overlapped and taped using sealing tapes. The floor boards and the skirting boards can then be reinstated. As sustainability becomes increasingly important and energy
prices continue to rise, upgrading suspended timber floors is an effective way to improve energy efficiency and optimise comfort levels, without compromising the character or integrity of the floor.
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