Indoor air quality – Ventilation and Airtightness
A designed and commissioned ventilation system is required in all certified Home Performance Index homes.
We spend 90% of our time indoors and we need to be sure that the internal air is healthy. A build up of a heavy gas like carbon dioxide affects the little people first, as it sinks to the floor, reducing their cognitive functions and ability to learn. In fact without ventilation in an airtight home we can quickly get a toxic soup of radon, water vapour, Volatile organic compounds, odours and other nasties. We are not good at opening windows in Ireland.
Homes are becoming more and more airtight as standards of workmanship improve. It is still permitted under current building regulations Part F technical guidance document, to use trickle vents or a ‘hole in the wall’ as background ventilation. If the airtightness is better than a certain value the area of these vents need to be increased by 40% defeating the purpose of the airtightness. It may still be allowed in the building regulations but that does not make it good practice. For starters the uncomfortable drafts from the trickle vents or hole is wall leads occupiers to block up the ventilation meaning they are living in a sealed box and this first manifests itself as excessive condensation and mould growth.
Sometimes home buyers and even some professionals find it hard to understand, why they should go to the bother of having a very air tight building and a ventilation system when you could just build a leaky building and skip the ventilation system.
However air tightness is one of the best indicators of the build quality and should be entirely separate issue to ventilation. Relying on leakiness for ventilation is bad practice as you can’t design bad workmanship. It also means uncontrolled means for air to come in, and for moist internal air to leave the building. In fact in a leaky building moist air could be condensing in the fabric of the house as it passes from the warm to the cold side of the structure, storing up future problems.
The solution is Build tight ventilate right! At the higher end we have Heat Recovery Ventilation, but there are also much cheaper and very effective solutions such as Demand Controlled Ventilation (DCV). However it is not enough to install the ventilation system, it needs to be tested to check that it is actually working which is why we also require commissioning certificates.
That is why we made this little video to explain air tightness and ventilation.