Sub Floor Spaces - The Engine Room of a House

Sub floor spaces create a great deal of water and air flow through your home most of this moisture is released from the subfloor soil, up to 0.4 litres per day for every meter square of soil, this may be higher in the winter months. Not removing this moisture and having poor ventilation can lead to damage of the building structure even as faraway as the roof void, this may also be causing ill health to the occupants from dust mites and mould.

Water can be released into the sub floor from various sources, downpipes and blocked gutters, rainwater not being cleared far enough away from the building, foul water drains, blocked drains, traps and burst water mains. Badly drained surface water, especially on poorly drained ground, causing water to pond and stagnate in the sub floor space. This is where proper ventilation comes in, a well ventilated area will help remove moisture from the subfloor, with little or no ventilation you may have a build up of moisture, your building materials will absorb moisture from the air the amount depending on the humidity, if the humidity is allowed to rise to 100% for long periods it can potentially bring the timber moisture content to 30% saturation point where timber if not properly treated will start to break down due to fungal attack, the exception being H3.2 treated timber most other treatments may break down in as little as 6 months or as long as 10 to 20 years if the moisture has not been removed. When the temp drops and moisture reaches dew point it can condense, this may be noticed on metal fittings like hanger's, nails and wires as water droplets and will gradually break down these fittings.

All this moisture can support fungal growth, lead to decay and insect infestation. The sub floor is often referred to as the engine room of a building circulating air and moisture through your buildings cavity and roof space, it is estimated that up to 50%of the air we breath may be coming from the sub floor, this may be filled with moisture much more than you would expect to find from any leaks, this problem may show up as excessive condensation on windows, mostly in the winter months.

This is where proper ventilation comes in removing moisture from the subfloor, up to 5 air changes an hour are required to keep the sub floor vented, in more severe cases especially poorly vented low laying areas you may need to add sheathing of a minimum of 0.25mm thick, this needs to be fitted properly, turned up at the sides and taped with joints lapped no less than 75mm. You may also have to consider field drains around the exterior walls to stop water gaining entry into the sub floor space.

This will all help to make your home a drier and healthier place to live, you may also find that at some point you have rid your home of some of the more unpleasant smells in your home.

Liam Hempsey is Managing Director of Pre-Purchase Inspections [http://www.prepurchaseinspections.co.nz], he has a long career within the building industry having worked in the UK, Scotland and New Zealand. Liam is a qualified Thermographer and currently undertakes professional pre-purchase inspections [http://www.prepurchaseinspections.co.nz] to help save property purchases check a property prior to purchase.

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