Articles for the Home Consumer

Roof Ventilation: Discover The Best Solution For Your Home

You live in a modern home. Surely you don’t need to concern yourself with roof ventilation or installing a roof ventilation system?

Although it sounds unlikely, that could be the situation. Modern homes are different from older homes. In the 21st century, homes are designed and built to conserve energy: designers aim for airtight homes and this presents challenges for ventilation.

Roof ventilation: your modern home may need it

Draughty older homes with high gable roofs rarely needed any additional roof ventilation, unlike modern roofs.

In an article in Issue 152 of Build magazine, Stephan Rupp, BRANZ Building Physicist, reports:

“Twenty years ago, roofs didn’t need to be specifically ventilated. Today, things are different. That’s because 21st century homes are more airtight, and if they aren’t aired, condensation may form.”

Condensation is mostly invisible and if unventilated, it’s destructive

A BRE publication, Building Research Establishment Digest, warns:

“If warm moist air from the building can enter the air space, it will condense on any surface whose temperature is below its dew point. This is most likely to be the underside of the cladding, from which moisture can drip on to the ceiling or damage the roof structure.”

It’s impossible to completely prevent condensation in your roof cavity. Condensation won’t cause damage if it evaporates. If it can’t evaporate and collects it can do great damage.

Why does condensation occur in your roof?

BRE Good Repair Guide 30 advises that of the water vapor produced in homes, up to 30% can find its way into the roof space:

“… through holes in the ceiling… (also) through gaps round light fittings… When the warm air meets the cold surfaces in the roof space, the water condenses out into water droplets.”

What damage can moisture and condensation create in your roof space?

Also from the BRE Good Repair Guide 30:

“In roofs with sarking felt or plastics sheeting under the tiles or slates, droplets can form, wetting the insulation and reducing its effectiveness, and ultimately damaging the ceiling. Electrical services may be wetted, leading to shorting. The moisture can cause staining or mould growth, corrode metal fittings, and, in the worst cases, lead to dry or wet rot in the timbers.”

Sadly, a lot of damage may occur before anyone in the home suspects there’s a problem and looks for a roof ventilation system.

Assessing your roof ventilation needs: check the roof style

If you live in a modern home and are unsure whether or not you need a roof ventilation system, think about the type of roof you have.

Stephan Rupp, in a report on passive roof ventilation, said that in modern homes:

“Skillion-type roofs are very popular, with a much reduced cavity volume. An easy pathway for moist air to migrate into the roof cavity has also been provided through open downlight fittings in the ceiling. These factors have created a situation where moisture can cause a problem in the roof space.”

If you know that your home has a low-volume roof cavity, you may need roof ventilation products. Another factor is important too: the type of roof insulation installed in your home.

Therefore it’s vital to get expert advice because so many factors are important when assessing your roof’s current ventilation, as well as whether roof ventilation products are needed.

Roof ventilation products: be guided by expert advice

You’ve been advised that your suspicions are correct: your roof needs a ventilation system. Naturally you’re concerned:

  • What type of products will you need?
  • How costly are roof ventilation products?
  • Can you do it yourself, or do you need a roofing contractor?

It’s best to get expert advice. A roofing tradesperson can assess the airflow in your roof space and can recommend products too.

Your primary aim in roof ventilation is to ensure that stale air is ventilated and fresh air constantly circulates. Therefore, recommended products will likely include vents. The BRE Good Repair Guide 30 has this good advice on vent installation:

“… a large number of small vents spaced evenly across the roof surface is preferable to a few large ones. However, if fewer, large vents are the only practicable solution, position them so as to avoid dead spaces.”

With the right advice, you can install a roof ventilation system which will eliminate challenges like condensation. Such a system will ensure you have a comfortable, well-ventilated and secure home.