How insulation works - in its most basic form, insulation works by trapping air within the insulation material.
As the air molecules are trapped within the insulation, their movements are much more restricted, slowing the transfer of heat through the insulation material by convection.
But there’s more to it than that…
In addition to convection there is also conduction and radiation and understanding how these work will help you understand how insulation works.
Heat is thermal energy and this thermal energy can be passed to other materials by the three methods mentioned above:
A simple way of explaining this is to think of the heating system in your house. The boiler heats the water in the boiler by conduction and convection. The convection process moves the water around the pipework where it passes its heat to the radiators by conduction. The radiators then heat the air by conduction and radiation. Finally the air heats the room and us by convection.
It’s worth pointing out that it’s impossible to stop the transfer of heat. It’s only possible to slow it down, and as insulation is a poor conductor of heat it’s our best means of slowing the transfer of heat from our homes.
Conversely concrete, steel or plaster are relatively good conductors of heat and therefore allow heat to pass through quickly.
The sole purpose of the insulation in your home is to slow, as much as possible, the transfer of the heat from inside your home to outside.
It does this by reducing:
The next question on your journey to understand how insulation works is to think about poorly fitted insulation.
Poorly fitted insulation could mean leaving air gaps around the insulation material and the fabric of your home or laying the insulation too thinly.
For example if you were to place a 390mm wide roll of insulation between two ceiling joists that have a gap of 400mm between them then you’re going to have a gap of 10mm which isn’t insulated.
You might think that it’s close enough and won’t make that much of a difference. However, that 10mm gap allows the air to circulate which in turn allows heat to pass through and escape by convection, conduction and radiation.
I'm going to complicate things a little further by telling you that you should also install a vapour barrier or vapour control layer on the warm side of the insulation and an air tightness layer on the cold side of the insulation.
These will stop or reduce water vapour entering the insulation from the inside and stop 'wind wash' (where air moving over and through the insulation draws heat out of it making is perform poorly).
Leading on from above, if you want to avoid allowing your heat to escape quickly you’ll need to make sure your insulation well fitted.
Thankfully this can be done quite easily by ensuring there’s a good vapour barrier (see below), there are no gaps, it’s a consistent thickness and you don’t store things on top of it that will compress it.
When trying to understand how insulation works it’s also important to realise that there are two main types of insulation and then each of these has lots of sub-types:
For obvious reasons the closed cell insulation will be the better performing insulation, although it’s also more expensive.
These are rating values for different materials showing how thermally efficient they are.
I’m not going to go into great detail here but I’ll give you the basics to help you understand as you’ll see these figures quoted when you look at different types of insulation:
It’s all well and good knowing how insulation works, but you should also know that increasing the insulation in your home increases the risk of condensation, which could cause damage in the future.
To avoid this risk it’s essential that you, or your builder, should install a good quality vapour barrie or vapour control layer to the warm side of the insulation. This stops water vapour passing through the insulation where it can settle on cold surfaces and condense.
This can even happen inside the structure of your home where it can’t be seen (interstitial condensation).
You should also install an airtightness layer to the cold side fo the insulation.
Hopefully at this stage you should have a good basic knowledge of how insulation works within your home. But to summarise; you’ll need to choose the best insulation you can within your budget by comparing the r-values and/or u-values.
Cheaper insulation will need to be thicker to achieve similar r/u-values to the more expensive insulations.
If you’d like to get a little more information on the different types of insulation available take a quick look through my various articles on the best insulations, spray foam insulation, blow in cavity insulation, rigid foam insulation and blue jean insulation etc.