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A Guide to Ventilation

Good ventilation in your home is not only important, it's now a legal requirement (if you rent). With good ventilation, your home will be healthier, drier, and a much nicer place to live.

What is ventilation?

Ventilation is the intentional introduction of outdoor or fresh air into a space. Ventilation is mainly used to control indoor air quality by diluting and displacing indoor pollutants, and creating a drier environment. 

Why does ventilation matter?

Poor ventilation allows moisture and airborne pollutants to build up inside your home. This can cause health problems such as asthma for you and other members of your household. Moisture can also make your home uncomfortable to live in and damage its structure and decor.

A 2010 BRANZ survey of the condition of New Zealand homes found that many were damp and poorly ventilated. The BRANZ House Condition Survey found that 66 per cent of subfloor spaces had less than the required ventilation rates. It also found that many houses had defects that could be attributed to excessively high levels of moisture. It also found that most bathrooms relied only on openable windows for ventilation. Only half of kitchens used mechanical ventilation to vent moist air to the outside.

When should you think about ventilation?

Planning a home or renovation

If you're building or renovating, ventilation should be considered early in the design process.

Good design should strike a balance between the need to introduce fresh, healthy air into your home and the need to maintain comfortable temperatures, so ventilation should be considered alongside passive and active heating and cooling options.

If you consider heating without adequate ventilation, you may end up with a home that's warm but not as healthy or comfortable to live in as it could be.

Homes built since the 1990s are much more airtight than older homes meaning that problems associated with inadequate ventilation have become more common. Because these homes have very low levels of background air leakage, if the occupants don’t open windows regularly and/or use extractor fans in wet areas, condensation and damp will occur even though the homes are insulated.

Passive ventilators are an option to help deal with this problem. Small ventilation gaps are built into the door and window frames which can be left open during the day as they are secure. The ventilation openings can be closed when required.

Balanced mechanical ventilation systems are another option. Some have a heat exchanger which extracts heat from the exhaust air to warm the incoming air from the outside. They are commonly used in colder northern hemisphere countries where houses are typically highly insulated and airtight.

Home ventilation on the Gen Less website has more information.

During or after construction

During the construction process and for a few weeks afterwards, you'll need to provide good ventilation to minimise your exposure to airborne pollutants such as formaldehyde from new building materials. It’s also a good idea to choose environmentally friendly paints, plasterboard products and thermal insulation, such as those which have the Environmental Choice New Zealand label.

In your existing home

Ventilation can be improved in an existing home without making significant alterations. Moving a door or window, or removing an internal wall might make a significant difference.

A well-insulated and draught-proofed home allows you to better control your ventilation, rather than being draughty and cold.

Older homes tend to be less airtight than more modern homes. This can allow for some natural ventilation – but can also mean they're draughty and harder to heat. As a general rule of thumb, houses built before the 1960s will be very draughty, and houses built between the 1960s and 1980s will be quite draughty. Homes built since will be quite airtight, especially if they have a simple shape and roofline.

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