Underfloor Heating
If you live in a traditionally built property, you more than likely have suspended timber floors. If they haven’t already been insulated, you probably have complained once or twice about draughts coming up through the floorboards or the floor being cold as ice on those chilly winter mornings.
Insulating exposed floors can be very tricky and is usually one of the most disruptive measures to install. If access can’t be made below through a basement or cellar, then you may have to lift the floor internally, which will involve removing all furniture, skirting boards, possibly reroute services and if the floor height needs to be raised to accommodate insulation depth, adjust door heights and thresholds. This will mean re-jigging your living arrangements or possibly moving out all together whilst the work is carried out.
When exploring the viability of insulating suspended floors we need to take account of the depth of the floor void, what the ground below is covered in or if it is bare soil. We also take into consideration how the joists are supported at either end and also mid span, (usually a dwarf support wall).
With suspended floors it’s very important to address ventilation too. The suspended floor is built so there is air flow beneath the joists to stop damp and rot forming in the void. In some areas of the UK, this also prevents the accumulation of Radon, a gas heavier than air which can accumulate naturally.
Over time, original subfloor vents may have been blocked for a number of reasons. You or previous owners may have purposely covered them to reduce draughts, not realising that this creates another issue. The external floor height outside may have been raised over the years by laying a new drive or a patio on existing surfaces, now blocking vents. In both these examples, the air flow would need to be reinstated and also checking carefully for damage this may have caused.
There are a few ways you can insulate suspended floors, the most common being, insulating between the joists with a rigid insulation board, either friction-fitted in place so self-supporting or using a mineral wool held in place with netting or battens. Similar methods of insulating between the joists include fitting a vapour barrier stapled to the joists to create pockets in between them, then using loose fill insulation and ply-boarding over.
In all cases, the joists should be insulated to stop thermal bridging too, but there are other issues to address. As you insulate between the joists, you reduce airflow, so it is crucial to reduce the moisture access since the joists will be less able to dry out. The joist ends in the walls may need to be treated so to reduce moisture travel and thermal bridging. The rule of thumb is to always maintain at least 150mm of air flow below the joists. These traditional methods of insulating would require the floorboards being lifted or if the void was deep enough access to fit from beneath up into the joists.
There now is a BBA-approved method where the underside of the floor is spray-insulated using robotic technology so an installer doesn't need to physically get into the void. A remote-controlled buggy is sent in through a vent or small opening. This is a technological breakthrough which has the potential to treat a lot of properties that were too difficult previously.
Insulating a solid floor is less risky but still very disruptive. The most common method would be to fit an insulation board on top of the existing floor and then fitting a floating floor above so as to avoid a thermal bridge with the existing base. A DPM (damp proof membrane) can be fitted below the insulation layer if one isn't existing in the original floor at install. With the new floor height, you will almost certainly need to adjust door thresholds, reduce the height of doors and reposition skirting boards to accommodate the new floor level, so this can cause major disruption along with added costs.
As with all insulation installs, we need to tackle the interaction with attached walls to reduce thermal bridging. Best practice involves insulating the walls as well as floors, and at the junction making sure there is a continuation of the thermal envelope otherwise it can be possible to get mould and condensation building up at skirting boards.
The cost savings– and possibly more importantly with insulating the floors, the comfort benefit– can be very rewarding. The majority of methods of installation are very disruptive but as the industry improves with technological innovations coming to market from companies like Q-Bot, draughty cold floors could become a thing of the past.
