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Homeowners are often house proud and with good reason. 

Buying a house is a huge investment, and not to be taken lightly. 

Unfortunately, at times even the best constructed properties can experience moisture entering via the subfloor. This could be condensation or other types of damp affecting your living space.

Some tell-tale signs that you have a moisture problem is a stale musty smell entering your home, condensation on windows, ceilings, and walls, mould growing on surfaces, and wallpaper peeling. 

If that’s an issue, it would be prudent to invest in subfloor ventilation to combat the impact of damp and safeguard the health of both the building and your family.

What is subfloor ventilation?

As explained in The Spruce, ‘a subfloor is a solid base underneath your floor covering that you depend on for the stability of a room’s floors and walls.’ 

It’s this space that’s generally dark and can become damp, leading to potential damage to the home and health risks to its occupants. 

Subfloor ventilation is a remedy for these risks and has been likened to ‘opening a window and forcing fresh, cool, and clean air through your house and out the other side.’

Just as your walls and floor work together to create a structurally sound system, so too subfloor ventilation creates a system that draws out the damp, stale air from your home and circulates fresh air under your floor. 

These two aspects of subfloor ventilation can restore the right balance of moisture in your subfloor, thus treating the cause of damp-related damage. 

Does a subfloor need ventilation?

Unfortunately, at times it’s the signs that damage has already been done that lets us know a subfloor needs ventilation. 

It could be that you notice excessive condensation in your home, or mould growing on the window seals or walls. The stale air, from the subfloor if not properly ventilated can flow into your home’s living areas, creating a musty smell. 

These signs are not just unpleasant; they can also be a health hazard. Stale and damp air are perfect conditions for mould, bacteria, and termites. 

On a human level, these can exacerbate symptoms of allergies, asthma, and other respiratory problems. Certainly not what you would like to expose your loved ones to. 

For the home itself, moisture in a building from the subfloor can lead to rotting timber (made worse if termites are present), which can compromise the structure and safety of the building. 

Without subfloor ventilation, these issues can lead to warped floors, damp and ruined carpets, health-compromising odours and bacteria, and costly damage. 

Beyond this, are other less visible risks such as radon gas and volatile organic compounds (VOC). Radon gas is a radioactive, odourless, colourless gas which is naturally occurring under certain conditions and can move through the subsoil and into buildings. 

VOCs, as the name suggests, are volatile compounds that exist in some furniture and other man-made products we often have in our homes. Without subfloor ventilation these compounds can build up, resulting in potential health damage to the occupants. 

How does subfloor ventilation work? 

A subfloor can be ventilated by placing vents on the external opposing walls in the subfloor of a building. 

Subfloor ventilation systems generally include powered vents and static vents that work together to extract stale, damp air and circulate fresh, dry air into the subfloor. 

There are different types of subfloor ventilation, but essentially, they work on a ‘suck and blow’ principle, with one ventilating fan sucking fresh, dry air into the subfloor and the other ventilating fan blowing that air into the recesses below. 

Depending on the area, ducting may be required to distribute the air. As the air is now able to circulate, it restores the correct moisture balance in the subfloor.

Some subfloor ventilation systems are on a timer, others utilise sensors that detect moisture in the subfloor and either increase or reduce power according to what is needed. This provides an energy-efficient solution that also ensures the vents work as needed rather than overcompensating.

What are the requirements for subfloor ventilation in the UK?

BS 525 Management of Moisture in Buildings states that 4.4 ‘Floors next to the ground and floors exposed from below should be designed and constructed so that their structural and thermal performance are not adversely affected by interstitial condensation.’

As a result, UK building regulations stipulate the requirements for subfloor ventilation in the UK.

Which is as follows:

  • Two opposing external walls should have ventilation openings placed so that the ventilated air will have a free path between opposite sides and to all sides
  • The openings should not be less than either 1,500 mm2/m run of external wall or 500 mm2/m2 of floor area, whichever is the greater opening area
  • Any pipes needed to carry ventilated air should have a diameter of at least 100mm
  • Ventilated air space must be at least 75mm from the ground covering to any wall plates and at least 150mm to the underside of the suspended timber floor
  • Ventilation openings must incorporate suitable grills to prevent vermin entering the subfloor without causing a restriction in airflow

Benefits of installing subfloor ventilation

BS 525 Management of Moisture in Buildings states ‘Moisture in buildings is a significant cause of many building failures, including some building related occupant health problems.’ 

Subfloor ventilation offers a homeowner peace of mind that their two most precious assets, their loved ones and their home, are protected from health issues and costly damage that could otherwise arise from moisture and gases in their home. 

How much does it cost to install subfloor ventilation?

The cost of installing subfloor ventilation will depend on several factors including the size of the building and any ducting required, the choice of ventilation products, as well as any existing damage that may first need to be addressed. 

To find out more about costs of installing subfloor ventilation contact the professional and experienced team at Atlantis Damp to arrange a survey of your property’s unique needs and a quote to protect your home with subfloor ventilation.