Crawl space ventilation unit trial

Posted Thursday May 01, 2014 by Eric Fewster

Crawl space Smartvent mechanical ventilation unit

Since 22nd March, I have a crawl space ventilation unit installed at my house. I installed it because I have a problem under my suspended floor of high humidity levels coming from damp ground conditions coupled with inadequate passive ventilation through the air bricks. Over time this has resulted in damp floor joists, the WME (Wood Moisture Equivalent) of which is over the recommended maximum threshold of 18%. The ventilation device comes from the US and is called Smartvent – it kicks in only when outside humidity levels are lower than crawl space levels. The relative humidity in the crawl space determines what moisture content the exposed floor timbers reach, so reducing ventilation on warm humid days means that this humid air won’t cool inside the crawl space (giving a higher relative humidity) nor cause wetting of the cooler surfaces (condensation), but only brings in drier air to do what it is supposed to do – which is to remove moisture from the crawl space and joists. This is all part of research that has been ongoing at my house since the end of 2012, which is being conducted by a PhD student and the AECB – hopefully it will in time inform better practice into retrofitting insulation into suspended floors.

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