How roof insulation works

Roof insulation is one of the easiest ways to reduce heat lost in your home and save energy. But how does it work?

Well firstly lets look at a piece of insulation. The most common types of insulation are blanket insulation and loose fill insulation. I’ll write another post on which is better, but for now, the two do essentially the same thing. They create a convection barrier to keep the hot air in.

Convection. There are 3 main ways in which heat is transferred. Convection refers to the motion of a fluid (be it a gas or a liquid) from a hot place to a cold place. If you pour some hot water into some cold water, the two mix, through convection, until they are both at the same temperature.

Similarly, the air in your house, which is hot, tries to mix with the air outside your house which is cold. Also if you figure that hot air rises, the roof is the most important place to stop it.

Conduction. Conduction refers to a materials ability to transfer heat through it. A poker in a fire is a good conductor. Touch the poker and it is hot, even the part which is not in the fire. Plastic is a bad conductor. That is why a plastic handle on the poker will reduce how hot it is significantly.

Air is a really bad conductor (remember though, air is a good convector)

So back to how insulation works.

Roof insulation is made of fluffy fibrous materials, that are good at trapping air in it (or at least slows down the air a lot). This air, is a rally bad conductor, and so reduces the amount of conduction going on. Since the air is essentially trapped, there is little opportunity for it to move, and so there is little convection going on. Boom. That is how insulation works

So why not just use a sheet of plastic? Plastic would work to stop convection, but it is would allow conduction to continue, and so be less effective.

So… in summary… insulation works by

• Trapping air in (and so stop convection)
• Using the trapped air to stop conduction