Foundation vents

Foundation vents are a good way of providing ventilation under a home, and have traditionally been used as a means of controlling moisture in under-floor crawlspaces.

Foundation vent 
Good ventilation under the house can prevent rot and termites.

How do foundation vents work?

If you have a crawlspace under your house that experiences moisture build-up, a foundation vent will allow it to escape, helping to prevent moisture damage to the foundations of your home. This in turn helps to prevent rot, mildew, instability and pest infestations (including termites).

Recent thinking, however, is that these vents alone may be less effective than other means. An alternative method (or at least something to use in conjunction with foundation vents) is a vapour barrier, which is a plastic or foil sheet laid across the ground or around beams to stop water penetration.

Ideally foundation vents would be installed in properties that sit high on a block, in areas where the climate is temperate all year round.

How effective are foundation vents?

There are several ways of getting rid of excess moisture from underneath your home, but foundation vents are the cheapest and most effective. That being said, they are often overlooked and are sometimes considered to be a drain on power consumption, thanks to added heating and cooling requirements.


Foundation vents can be active or passive. A passive foundation vent is simply a permanent opening in the side of your home, covered by a grill. While this allows natural ventilation to the area under your home, it can cause issues in winter months by allowing cool air in underneath the floor. To counteract this, you can insulate the area between your crawlspace and floor with a vapour barrier, or opt for an active foundation vent which can be opened and closed, either controlled manually or automatically via a timer or a sensor.

  • Helps prevent rot, mildew and termite infestations
  • Passive and manual models cost nothing to operate
  • May allow unwanted water into your crawlspace
  • May make your home hotter in summer and cooler in winter