As the emphasis on healthier energy-efficient homes with warmer, dryer living conditions grows in New Zealand, the building industry has seen a rise in the emergence of more passive housing trends, including more airtight construction methods and associated products.
While making our houses less drafty is great, building airtight homes without proper moisture management can lead to moisture build-up, issues with mould and mildew, and deterioration of the building materials, which eventually compromises the watertight properties of the house.
Roofing Ventilation Options
While traditional gable style roof design using either corrugated iron or concrete tiles usually provides some degree of self-ventilating properties, the use of different construction techniques such as skillion and mono-pitch roof lines has left some roof spaces facing poor ventilation. This is usually where the need for roof space ventilation arises, either passive or mechanical.
Passive Ventilation
What is passive ventilation? The basic principles of passive ventilation are reasonably straightforward; if there is a temperature or pressure difference, under the laws of equilibrium, the environment will try to equalise itself. For the roof space, this results in the movement of warm air upwards toward the roof peak driven by the introduction of heavier colder air that sinks to the bottom of the space. This continuous movement of air through a building or roof space reduces condensation and refreshes the air preventing the likelihood of mould and mildew growth and moisture build-up.
Mechanical Ventilation
Sometimes it is necessary to use a system of mechanical vents to ventilate a roof properly. Mechanical ventilation is often seen on commercial buildings and requires a power source to provide constant airflow and circulation. Mechanical or automated roofing ventilation options are necessary if the design of the roof doesn’t allow much natural airflow or the building is in an area without much wind.
Why Is Roof Space Ventilation Needed In NZ?
As houses are being built more airtight, they are unable to “breathe”. This means they cannot follow the natural process of sucking in fresh air and expelling stale air containing moisture and contaminants. If this humidity is not removed from the building, it can lead to condensation. The continuous build-up of condensation leads to the eventual decay of building products and mould growth.
The good news is proper ventilation can reduce the risk of these problems. Maintaining your home’s roofing ventilation is especially important in NZ because we experience both cold and hot weather to varying degrees around the country.
Roof Damage Caused By Poor Ventilation
Hot air is trapped in your home during the summer can make it harder to keep cool while also aiding in the formation of condensation, causing issues like mould and mildew. Other types of damage due to a poorly vented roof space are:
- Rust in nails, screws and iron
- Roof leaks
- Reduced effectiveness of insulation
- Mould and mildew growth
- Pests or unwanted animals or insects
- Excessive heat in the roof space
- Rot and water damage to trusses
- Ice dams along the edges of guttering when it snows
How Do You Know If You Need To Install Roof Vents?
While the NZ building code provides clear guidelines on ventilation inside the home, ventilation of the roof space is not as clearly defined. However, there is no need to panic – there are plenty of roofs in New Zealand that perform their job perfectly well without any added ventilation.
Buildings with good humidity controls and airtight ceilings without things like downlights or other fixtures that provide a means for the moisture-laden air to enter the roof space generally don’t experience condensation problems in their roof cavities.
However, there are always exceptions to the rule, so it’s more a case of homeowners having to ask the question; either of your builder or roofing installer if you are installing a new roof, or carrying out some simple checks on your existing roof. For new builds, the contributing factors you will need to consider are; exposure to wind, type of roofing materials used, and your home’s roofline.
The easiest way to check an existing roof is to make it a part of your regular yearly roof checks. Condensation is particularly visible in the colder months of the year, between April and July. You may see droplets of water or condensation, sometimes known as ‘roof sweating’ or damp patches on the framing or within the insulation. You might also notice a musty smell and, in the extreme – black mould growing on items stored in the roof space, timber, or roof lining.
Sometimes the cause of mould or moisture in the roof space can be due to a leaky roof. See here for more information on the 10 most common causes of roof leaks or more information on how to tell if your roof needs replacing.
How Can I Improve My Roof Ventilation?
It is important to note that for adequate ventilation to work, a balance of intake (lower) and exhaust (higher) venting is required. There are several key areas in the roof space that provide logical ventilation points for excess heat and humidity, these are:
- Ridge Vents. Ridge vents (exhaust) are the obvious place for allowing warm moist air to escape as it naturally rises toward the top. A ridge vent has a solid top and small gaps on either side, ridge vents require the presence of soffit vents to best encourage air flow through the roof space.
- Soffit Vents. Best for allowing air to enter the roof space (intake), soffit vents can be placed anywhere along the soffits under the eaves and can be circular or continuous. It is important to ensure soffit vents are not covered by insulation.
- Gable Vents. Commonly installed in steeper roof pitches to create airflow via cross-breezes, effectively moving hot moisture-laden air out of the roof space. Gable vents are sometimes called gable louvres.
- Vent Turbines. Turbine vents are designed to pull heat and humidity from the roof space. Powered naturally by wind, turbines are a good option where complicated rooflines make natural airflow difficult.
- Mechanical Vents. These types of roof vents require a power source and are particularly useful where there is little or no wind or in a commercial setting.
3 Benefits Of Proper Roof Ventilation
Ensuring your roof has proper ventilation has ongoing effects not only on the health of your home but the occupant’s health.
- Greater Energy Saving. Poor ventilation often results in high temperatures in the roof space; this can affect the rest of the home and lead to higher electricity bills due to added pressure on air conditioning and HVAC units.
- A Healthier, More Comfortable Home. Less likelihood of toxic mould and mildew, which can pose health risks to you and your family.
- Prolonged Lifespan Of Your Roof. Looking after the materials your roof is made from will prolong its expected lifespan.
The information provided in this article is designed as a general guide only; for more details on how passive ventilation can be incorporated into roof spaces it is best to contact your local roofing installer.
