What to consider when retrofitting floor insulation

9 May 2019 Kingspan Insulation UK

Although adding or replacing floor insulation may seem like an easy task, there are a number of different points to consider before starting any work.

Type of floor
  • Depending on the construction of your floor, different methods of insulating may be appropriate, from solid floor to suspended timber floors to soffits. See our flooring applications page for all the details.
  • Level access and thresholds
    • When adding insulation to a floor depends on the type of floor as to what affect it will have on level access to the building. Suspended floor insulation will fit under existing floorboards but adding insulation over a concrete slab might impact level access from outside spaces to the dwelling.This may result in a step at thresholds, but this could be reduced or negated by using insulation with a lower lambda value. This would mean a thinner build up to achieve the required u-value and remove the need for a step at the threshold.
  • Especially for suspended timber floors, it is important to make sure that any work carried out does not block up any ventilation grills or bricks as this might lead to moisture build up causing issues with the fabric of the building.
  • Damp proof membrane
    • A key consideration for retrofitting floors is if a damp proof membrane is present as this will affect the insulation chosen. Further details about what to look for on this are in our article on DPM.
Skirting boards, radiators, pipe work
  • When adding insulation to a floor, it may become necessary to raise the floor height to accommodate this, resulting in further work being necessary in raising pipework, radiators and skirting board. If an insulation with a lower lambda value is chosen, then thinner insulation can be used to meet the target u-value and it may be possible to keep the floor level the same, removing the need for further remedial work.
  • Underfloor heating
    • A common improvement when renovating a floor is to add underfloor heating. The type of underfloor heating chosen can affect the choice of build up for the floor and where the insulation is in relation to the heating system. The main consideration is if it is an intermittent heating system or a continuous underfloor heating system. Briefly, for the former, the insulation should go below the heating system and above the concrete slab, for the latter the insulation should be underneath the concrete slab. See our article on underfloor heating for more information.
Thermal bridging
  • Thermal bridging heat losses at the floor edge where it joins with the wall can lead to a risk of surface condensation and mould growth if not adequately addressed. For retrofit, it’s difficult to fully address every eventuality, but there are some common principles that can be considered:
    • Isolate the thermal bridge through insulation by using a layer of ‘perimeter upstand’ insulation to minimise direct contact of the thermal bridge with either the inside or outside temperature.
    • Increase the thermal bridge heatflow path e.g. by overlapping wall and floor edge insulation to make the heat travel further to escape, raising internal surface temperature and lowering risk.
    • Change the thermal bridge materials – e.g. by introducing a lower conductivity material into the wall construction adjacent to the floor (for a new build construction, this might involve using a suitable lower conductivity lightweight aerated block in proximity to the junction for example.
Thickness of insulation 
  • To work out what thickness of insulation you need, you can visit our online u-value calculator, which will show you what u-value can be achieved in different build ups.