Dealing With Inadequate Sub-Floor Ventilation

Copyright (c) 2015 Matt Reardon

Insufficient ventilation may lead to elevated moisture levels in the unguarded underside of your flooring, dampness in the home, and other structural problems. A sub-floor is that crawl space created between the ground and the lowest floor of your building. When this space gets exposed to high moisture levels, it promotes fungal decay as well as possible attack by timber pests like termites which thrive in damp and moist areas.

In a study of building structural characteristics linked with high indoor air organochlorine termiticides concentrations, published in the Australian Journal of Public Health Oct 1993 issue, it was found out that the most widespread causes for these structural problems are to be found on the external of the house, typically from surface and roof water drainage.

Ideally, all crawl spaces and sub-floors ought to be viewed as having potential water and moisture problems.

Your sub-floors are going to remain drier if you build and maintain them along the following lines:

- Roof Drainage: Divert from the house all water coming from your roof and gutters. Don't let roof drainage water to saturate the soils that are around the house foundation. Remember that your gutter system requires regular maintenance and cleaning to ensure proper operation.

- Yard Drainage: Slope the soils surrounding your house in a way as that diverts the water away from your house.

- Tree limbs that are overhanging your roof and gutters will make their cleaning and maintenance more challenging and may greatly contribute to your drainage problems.

- During new house construction, have the foundation exterior carefully sealed. In addition, install a good quality house perimeter drain system. It is also recommended that you put into place a separate drainage system for your gutters plus downpipes.

To avert the deterioration of your timber floor construction ample ventilation should be given to the whole sub-floor area. The moisture that is coming from the ground has to be stopped from causing unnecessary dampness or in contributing to the deterioration of the building elements. The Second Volume of the Building Code of Australia (BCA) stipulates that the minimum clearance between the lowest frame of your building and the ground surface must be not be below 150mm. Additionally, clearance should also be in compliance with any requirements coming from the manufacturers of the materials used in the flooring.

In addition, your sub-floors will stay drier if you observe the following precautions:

- Storage: Majority of crawl spaces or subfloors are indeed too small to be utilized for any meaningful storage. Moreover, to store stuff and materials in there often will be contributing to reducing vitally needed air circulation. This could create an atmosphere that is conducive for pest infestation such as rodents.

- Head room: Crawl spaces that are larger tend to keep drier; they also allow for additional air circulation besides making repair and maintenance easier.

- Venting: Though the advantages of venting your crawl spaces remains debatable, the majority of building codes advocate for some form of crawl space vents. In a study whose results were published on the Building and Environment Journal in 1998, it was shown that air concentration strongly depends on wind velocity in any given space. The study was looking into the impacts of subfloor ventilation and protective measures against toxic soil vapours.


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Matt Reardon is a technician at MouldBuster. He will ensure that the home projects you are planning are within the set regulations. Come to MouldBuster and Matt will only be too happy to lend a helping hand. If you need more advice regarding the service browse our page at http://mouldbuster.com.au/sub-floor-ventilation/ .