Floor Insulation

  1. Checking for damp and good preparation
  • Before starting the installation of any floor insulation, it is necessary to check and prepare the floor first.
  • Having removed the floor boards, it is important to check for any damp issues, or signs of wood rot. This will need to be addressed first, before installation can begin.
  • Rotting wood can be replaced to ensure the structural integrity of the floor.
  • In addition, it is imperative to establish whether there are any condensation causing, underlying factors that need addressing. A moisture meter can be used to asses this, moisture content of any wood should be below 14%.
  • Checking adjoining walls for moisture, visually looking for rusty pipes, knowing if the property has a history of being flooded, or historical leaks that have not been properly addressed, will allow you to seal and fix any issues thoroughly before beginning installation.


  1. Ventilation Assessment
  • Not only does floor insulation create a good thermal barrier to keep the heat from escaping a house, it can also cover gaps between the floor joists to prevent air draughts circulating through a home.
  • However, it is necessary to ensure that a house is still well ventilated. This is in order to let in fresh air and to effectively extract moist indoor air before it condenses and causes potential damp issues.
  • How to ensure excellent ventilation around a house:
  • Check and clean any existing ventilation channels. Clean air bricks and air vents to ensure smooth circulation of air.
  • Remove any blockages, debris under the floor boards to make sure that air can flow freely. Anything that restricts airflow will lead to poor ventilation under the floor.
  • Check/Install additional ventilation measures. This can be in the form of extraction fans in normally wetter areas like kitchens and bathrooms.  Alternatively, measures such as room vents and window vents can be added to ensure good ventilation and airflow.


  1. Address any other practical issues to facilitate ease of installation

Clear up any obstructions to start working in an efficient manner.  Make sure that there is not extensive piping or cabling that will prevent laying insulation in between the floor joists.


Installing suspended wood floor insulation from below the joists

If the floor has a void/crawl space, or a cellar, any insulation can be fitted from below and without the need to remove the floorboards.

  1.  Measure the gap between the floor joists and cut the insulation boards accurately to attain a snug fit. Measurement is key here, although any small gaps can be filled with expanding urethane sealant.
  2.  The insulation boards will then need to be pushed in until they fit up against the floor boards, again trying to ensure that there are no air gaps.
  3.  If installing 2 layers of insulation, offset the joints between the two layers.
  4. Insulation boards can either be fixed in place by batons nailed to the joists, or by driving galvanised nails through the boards and in to the joists at a 45-degree angle.
    5. Insulation boards may need to be cut for narrower pieces, to fill smaller gaps.  The boards should also be nailed in to supporting blocks and attached to perimeter walls.  Any gaps less than 25mm can be filled with expanding sealant.  This will ensure a uniform coverage with no gaps.


How to install suspended timber floor insulation from above the joists

If there is no way to get access from the joists below, then you will need to clear the room, lift up the carpets/flooring and remove the floorboards before you can start. Once this is done, the installation process is very similar to the above, but in reverse order:
1.    Measure and mark the joist at the required depth to install the insulation so it will sit flush with the floorboards once it has been fitted.
2.    Side-nail the timber battens or partially drive the galvanised nails into the joist as described above.
3.    You can then cut and fit the boards, as detailed above.

Heating Measures

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