For optimum results when addressing heat loss through a suspended timber floor the specification needs to ensure that high levels of thermal performance delivered by the insulation material are combined with airtightness and moisture control while at the same time facilitating a degree of breathability.
Vapour control layer suspended timber floor.
Breather membranes are positioned to the outside of the insulation acting as a weather barrier while still allowing moisture particles to escape from the inside.
This ensures air leakage is minimized and the risk of interstitial condensation is further reduced.
To answer your question introducing a vapour barrier to the underside of the floor joists would be a complete waste of time that is other than to assist in the air tightness of the building which is another bone of contention whereas introducing a vapour barrier over the top of the floor joists may well provide some long term benefits by reducing the amount of water vapour introduced to the timber.
Rising moisture is a huge issue for many people.
This helps to minimise underfloor condensation and hence the risk of mould or decay while improving the thermal efficiency of your floor and building.
Suspended timber floor hybris is fitted between joists and can be faced internally with hcontrol hybrid the vapour control layer or externally with boost r hybrid the breather membrane.
Make sure that the air vents in the crawl space below the membrane and insulation are not blocked and that there is plenty of ventilation to help remove any moisture under the floor.
We need to make sure that the ventilation under the suspended timber floor is adequate to stop moisture build up and damage to joists and floorboards.
They provide adequate support for the insulation and are recommended for use in suspended timber floor constructions.
Finally an intelligent airtightness and vapour control layer such as pro clima intello plus or a vapour check such as pro clima da must be applied and sealed on top of the floor joists prior to the floor boards being reinstated.
Tyvek membranes are ideal for suspended timber floor construction.
Tyvek supro membranes are sturdy and durable.
Vapour control layers are positioned to the inside of the insulation in order to minimise the amount of warm moist air entering the construction.