Help for protecting your roof from moisture build-up

Get tips for understanding, controlling and preventing the buildup of moisture and condensation in your home’s attic and roof space.
Modern building methods and insulation materials provide excellent protection for your home’s interior against the incursion of seasonal cold from outside. Most homes have insulation laid above the ceiling in the roof space. This is very effective for keeping the home warm and conserving energy, but it also prevents most of the heat from entering the roof space. This makes it more likely that condensation will form because surfaces in the roof space remain cold.

Condensation is a result of water vapour coming into contact with cold surfaces to form dampness or water droplets. When warm, moist air encounters a colder surface it cools and releases water vapor onto nearby surfaces and into the surrounding air, causing condensation.

Water vapour is a natural result of common daily activities that take place in the home, such as breathing, bathing, cooking, washing and drying clothes, and operating appliances. If this water vapour is not allowed to exit the structure through an open window or air vent, it will be carried in the air until it encounters a cold surface (such as the roof space) where it will cool and form condensation.

Most building materials are porous and allow water vapour to pass through gaps around cables and pipes, light fixtures and other home features. It’s impossible to prevent condensation in the roof space completely, but there are some ways to control the amount of water vapour present inside your home:

• Use lids on saucepans while cooking to reduce steam
• Don’t dry clothing on a radiator or by hanging it indoors; use a tumble dryer that is properly vented through an open window or outside wall.
• While washing dishes or clothing, cooking, or bathing use an extractor fan or open a window to allow water vapour to escape.
• Wipe away any condensation you notice on mirrors, vanity tops and other surfaces.

Once moisture and water vapour have infiltrated the roof space, the most practical and effective method of removing it is by ventilation. Most pitched roofs include ventilation slots that are located at two opposite eaves, providing an air flow across the roof space and using the natural forces of wind pressure and heat transfer to remove water vapour from the interior. If you notice condensation in your roof space, the very first thing you should do is check to see if the ventilation slots have become blocked.

If ventilation is in place and unblocked, but condensation persists, you might need to seek professional help and advice from qualified roofing contractor.