Sub Floor Ventilation: A few things you need to know

Sub Floor Ventilation

Do you need a Sub Floor Ventilation system?

It’s easy to forget that the area under your home needs ventilation. After all, you’re not down there to notice the air quality. But that doesn’t mean it’s not important. If there is a problem with the ventilation under your house, it can affect your living environment. Moisture underneath the home might get your attention with a musty smell or sunken floorboards. This is because a moist environment rots timber and allows mould growth. Even worse, damp or rotten timber is a great  place for termites to make a nest. In the worst case scenario, damp from under the home causes illness. Preventing dampness under the home or fixing it early will keep you and your family healthy. Making sure that you have proper sub floor ventilation is an essential step to fixing these problems.

So how do you tell if there is a problem is under the home?

Most people don’t realise that there’s a problem with the sub floor until it becomes a problem in the main house. As we’ve already mentioned, odours and sunken floors might indicate a problem with the sub floor, but there are other signs too. Moist air in the living space can come from underneath the house. So if there’s a lot of condensation on your windows, or the house feels humid, it’s time to take a look at the ventilation of the whole house, including the sub floor.

If it’s possible to check the crawl space for signs of condensation, mould or rot, then you should. Investigate any signs of water under the home, eg. discoloured timber. Try and identify the source of the water:

  • Is there a leaking pipe?
  • Are there signs of condensation?
  • Is there any visible mould or mildew?
  • Can rain water come in?
  • If there’s a smell, is it stronger in the crawl space?

Not everybody can get down underneath their house, but if you think there might be a problem, it’s certainly worth asking a friend or relative to check it out for you.

Where does the moisture come from?

Moisture winds up under the house in a number of ways. Some are less obvious than others. It’s easy to diagnose a drip from a leaky pipe, or a puddle where rain water may have poured in through a gap in the building. It’s harder to tell if the moisture is coming up through the soil. Surface soil might appear dry, but hide a lot of moisture.  As the moisture evaporates, it comes up through the soil and under the home. Without adequate ventilation, this moisture is trapped under the house with no way out. This is why the air under the home might feel damp, even if there’s no visible water source.

How do we fix it?

If the problem is caused by a leak under the home, the first thing to do is seal it up. Once you’re sure that you’ve patched up any leaks, and drained out any excess water, it’s time to think about ventilation.

Without ventilation, the humidity under the house has nowhere to go. Even if there are existing vents, the air flow might not be fast enough to extract the moisture. In this case, you need an exhaust fan.

For sub floor ventilation, we recommend aiming for between 6 and 10 air changes an hour, but it depends on the severity of the problem. If there is a lot of moisture under the house, you will need a fan with a higher extraction rate. Use our calculator to work out the capacity of the fan you need.

Pure Ventilation stocks a range of sub floor ventilation kits. These kits have everything you need to solve this problem, including an inline fan, ducting, vents…even tape! This kits are made for DIY installation, as long as you have a power point to connect the fan to. If there’s no existing power point (often the case for sub floor systems) an electrician can install the fan and anyone with a bit of DIY know-how can do the rest.

Getting the most out of sub floor ventilation

There are a few things to consider when you install a sub floor system:

  1. The fan needs to be the right capacity for your purpose.
  2. At least two sides of the sub floor area need vents, to create a cross flow.
  3. Make sure the vents aren’t blocked. There needs to be a clear path for air flow.
  4. Any ducting needs to be kept as straight as possible. Be careful not to tear it during installation.

As a general guide, following the above principles will improve the ventilation under your home. If you need advice about sub floor ventilation, contact us.

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