Underfloor Insulation

Anyone living in a cold damp climate will know that insulation is the key to comfort. Not only does it prevent heat from escaping, thus maintaining a comfortable internal environment, but it also acts as a barrier against moisture entering your home from the damp ground outside.

Since a damp home is much harder to heat, this will save you a fortune in energy bills. Moisture seeping in, together with drafts of cold, damp air which push warm air up towards the ceiling, cause condensation, which leads to the growth of mould and mildew which is both unsightly and unhealthy.

Underfloor insulation is especially important in keeping feet warm and playing children free from chills – Wooden Floorboards are particularly susceptible to cold and moisture seeping through the cracks and gaps, as well as being permeable in themselves.

Insulation is even effective in summer or in warmer climates, helping to keep the home cool and generally providing an even internal living temperature all year round.

So How Does it Work?

Most insulation works on the same principle: pockets of trapped air which form a barrier and prevent the transmission of heat, because air is a very poor conductor of heat.

The smaller the pockets, the stronger the barrier, therefore the best insulation materials have small cavities.

This can be so powerful that it can retain heat in the most extreme cold, as seen in nature with birds and animals living and raising vulnerable offspring in extremely low temperatures.

Another, less popular, method of insulation is by reflection of heat – usually achieved through silver foil. This way, any heat leaving the house is reflected back in again.

What Kind of Insulation Should I Use?

There are three main types of underfloor insulation available on the market:

Fibre-based – these are constructed in web form – a bit like a wool sweater – which slows the movement of heat across them.

Materials used are either fibreglass or polyester, with the former being more commonly used as it tends to outperform other materials. It is also cheaper and does not burn, although it can melt at high temperatures, such as during a great fire.

However, it is not environmentally friendly as it is not renewable and it has raised some health concerns, particularly with regards to fibres causing irritation to skin and the respiratory tract. This is especially relevant during installation.

Polyester does not seem to cause these health concerns – but it is still a non-renewable resource and it does not perform as well as fibreglass. It is also slightly more flammable, although it burns very slowly, with a dense smoke.

Polystyrene – this is a common insulator used in all aspects of daily life, from the foam coffee cup at takeaways to the freezer section of your supermarket.

It is a very poor conductor of heat which is why it is used so widely and it is as effective in the home environment, as underfloor insulation. It is usually available in sheets, fitting between floor joists – some in a tight fit and others leaving an air cavity between for further insulation.

They are often used under concrete floors and you can even get hollow polystyrene blocks filled with reinforced concrete.

Unfortunately, it is also not environmentally-friendly as it is a product of the petrochemical industry and it also burns in a fire to give off toxic fumes, although this can be reduced if it is sealed under concrete slabs in the floor.

Foil – usually made of aluminium-coated paper, foil works by reflecting any heat which escapes through the floor back into the house. It also acts as a barrier against cold entering from the outside. It is an effective insulator and generally an economical choice for underfloor insulation, although it requires a sealed air gap for correct function.

Nowadays, you can also get insulation material that is a combination of fibreglass and aluminium foil, getting the best of both worlds.

As an environmentally-friendly alternative, pumice is a good choice for insulation under concrete floors, as it is a renewable, natural resource and can be economical if it occurs locally.

How do I Install it?

In general, it is best to leave things to professionals as even the best insulation will be useless if it is installed badly. In some cases, insulation will have to be installed at the time of construction, such as with concrete floor slabs.

If you do decide to attempt DIY installation, here are a few things to keep in mind:

  • When installing fibreglass, try to wear full protection, such as gloves, long-sleeved shirts and trousers and a face mask, to avoid skin and respiratory irritation
  • Take great care around wiring (especially when handling sharp objects) and make sure you do not place insulation over wiring as this prevents them from cooling properly.
  • If fitting polystyrene, take extra care to avoid wiring as a chemical reaction would result, leading to damage to the wire.
  • Make allowances for potential water leaks when installing insulation and take care with plumbing.
  • Make sure you have adequate lighting to see what you are doing but at the same time, be careful of hot lights causing fires or burns.
  • Try to have another person on hand to help and supervise as installation can lead to dangerous accidents.

Although floors only account for about 10% of the heat loss from a household, insulation is generally cheap and easy to install so it is still worth doing.

In any case, no matter what the cost, you will always regain your initial investment over time from the great savings on energy bills.

See Also
Underfloor heating pipes
Underfloor Heating: Water Based
Electric floor heating control
Underfloor Heating: Electrical