Ventilation
- Pic: Craig Robertson Photography for Beacon Pathway Ltd
With good ventilation, your home will be drier, healthier and more comfortable.
Ventilation is about helping air to circulate in your home. It allows moisture and airborne pollutants to escape, and fresh, clean air to be drawn into your home. Well-designed ventilation will provide cooling in summer. In winter, it will let stale air out but keep warmth in.
Effective ventilation depends to a significant extent on the size, placement and type of windows, doors and other openings in your home. With good design, air will be circulated without creating draughts.
You'll need extractor fans to expel moist air from the kitchen, bathroom and laundry outside.
Does ventilation matter?
Yes. A 2005 BRANZ survey of the condition of New Zealand homes found that many were damp and poorly ventilated.
Most bathrooms relied only on windows for ventilation. Only half of kitchens vented moist air to the outside. And 40% of timber-framed homes had poor or seriously inadequate subfloor ventilation.
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.
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 heating and passive cooling options. If you consider heating without ventilation, you may end up with a home that's warm but not as healthy or comfortable to live in as it could be.
During and 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.
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.
For ventilation to work as effectively as it should, your home should be well insulated.
Note that older wooden 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.
Passive ventilation
How does it work?
Passive ventilation uses doors, windows, vents, louvres and other openings to bring fresh air into your home and let stale air out. The size and placement of these openings can be used to guide air into and through your home.
Where cooling is required, windows or other openings on upper levels can be opened to let warm air escape. In winter, well-designed passive ventilation refreshes the air in your home without creating draughts or letting out too much heat.
Passive ventilation can only work if air has clear, uninterrupted pathways through your home. You can maximise air flow by designing open plan areas or having high vents or other openings between rooms. In general, windows should be larger on one side of the home than the other in order to encourage air flow.
If your home is designed for passive ventilation, all you'll need to do is open and close windows, doors or other vents as needed to reduce the temperature and improve the quality of the air you're breathing.
- To encourage cool air flow, you'll need larger windows opening to the breeze and smaller, higher windows on the walls on the opposite side of the house
Options
The appropriate ventilation options for your home will depend on the climate and microclimate of the area you live in, and what prevailing breezes there are. As a rule of thumb, the area of windows, doors and other vents that can be opened up to the outside should be at least 5% of the floor area for each living space - and more for high-use areas.
Some points to consider:
- Windows or other openings on opposite sides of your home will help draw air through.
- Opening windows on the south and east side are best for allowing cool breeze into your home from early in the day. Openings on the north and west sides, higher up, will keep the air moving.
- Vents or other openings in the roof or on upper floors will allow air to escape as heat rises.
- Built-in vents, louvres, slots and gaps in door or window framing can provide low-level ventilation over long periods without creating draughts or security risks.
- Different types of window can be used to guide air into your home.
- If your home is on more than one level, make sure there are opening windows and doors on each level.
See glazing for more about window design.
Background air leakage
Some features will aid ventilation by providing low-level background movement of air between your home's interior and exterior. For example:
- timber joinery around windows and doors
- flues and chimneys
- recessed ceiling and light fittings.
Active ventilation
Active ventilation is ventilation provided mechanically - for example, by fans, range hoods and forced air ventilation systems. These systems run on electricity - the bigger the system and the more components, the more power it will use.
A well-insulated, warm home may only need to use active ventilation for rooms where moisture is generated (bathroom, laundry and kitchen), while passive ventilation will be sufficient for maintaining air quality through the rest of your home.
Active ventilation may also be needed to get warm air into cooler, damper areas such as south-facing rooms.
Extractor fans/range hoods
Extractor fans quickly remove moist air from bathrooms, toilets and laundries. Range hoods do the same job for kitchens.
It's important to choose the right-sized fan for the job. A fan that's too small won't remove enough moist air to keep your home dry. A fan that's too large can create draughts. Minimum requirements for extractor fan performance are set down under the Building Code.
Extractor fans should be placed as close to the moisture source as possible.
Because extractor fans remove moist air but don't bring in fresh air to replace it, you'll need some other way of getting fresh air into the room. By placing air vents on the opposite side of the room from the extractor fan, or slightly opening doors or windows, you can encourage air flow.
Forced or positive pressure systems
These systems blow dry air into your home from the roof space above the ceiling (the roof space is usually warmer on sunny winter days).
With this type of system, positive pressure forces moisture out through the walls and joinery. These systems are more effective for retrofits of older homes with roof space than modern, airtight homes with no roof space or space for the air to be pushed through.
Air filtration is needed to minimise pollutants from the roof space.
Heat recovery systems
These extract warm, damp air from living spaces, recover most of the heat, use it to warm up cold, dry air from outside, then pump it into the house. Heat recovery systems can work even where there is no roof space. These systems meet Building Code requirements for using fresh outside air.
In some locations a solar-powered system may be suitable.
Heat recovery systems will never recover all heat - you'll still need some other way to keep yourself warm. They're more effective in airtight homes. Every home is different - so the system has to fit with your needs and building design.
More information
From Smarter Homes
From consumer.org.nz
Note: you may have to be a subscriber to access some of this content.
From ConsumerBuild
From other sites
The Energywise website has information about window design and placement and about draughts. The Asthma Foundation has information on dealing with dampness and pollution-free homes.
You can buy BRANZ bulletins on passive ventilation, ventilation of enclosed subfloor spaces and preventing construction moisture problems in new buildings from the BRANZ website (click on the link to the BRANZ bookshop).
