Insulation vs air tightness: which is more important?

The controversial Insulate Britain protests have grabbed headlines in the UK for some months. And while many understandably take issue with the group’s tactics, they have at least brought the topic of insulation into the public discourse.

But how important is insulating homes compared to air tightness, and how do they relate to ventilation?

Insulation

While images of protesters blocking major roads have infuriated many – arguably with good reason – the simple truth is that a well-insulated home can prevent a lot of heat escaping.

Around 25% of heat in an uninsulated home is lost via the roof. By adding loft or roof insulation, a homeowner could save in the region of £175 per year on heating bills – equating to about 11% of energy costs. It’s equally good for the environment, since about 1 tonne of CO2 emissions are cut over the same period.

A well-insulated home will mean more comfortable temperatures in both winter and summer.

Air tightness

But with all the focus on insulation, the importance of air tightness can be forgotten.

Some estimates suggest around 15% of total heat produced in the average UK home is lost through draughts. This percentage can rise significantly in a well-insulated home. Airtightness is, therefore, a critical element to consider when building low energy properties, since the effectiveness of insulation is massively reduced by insufficient air tightness.

Air tightness layers are commonly made from OSB, airtightness membranes or from good old-fashioned plaster.

Ventilation

Ventilation has also hit the headlines over the last two years due to coronavirus, since good ventilation helps reduce the transmission of Covid-19.

But it’s also important for maintaining air quality – by eliminating contaminated and stuffy air.

Of course, ventilation has to be balanced against insulation and air tightness. Too much ventilation will see too much energy lost through heat escaping.