by Refresh PSC »
Wed Apr 25, 2012 1:12 pm
The "Dutch" airflow system where circular air vents are inserted at approximately 300mm intervals horizontally along the perimeter of the property do not work. In principle, the system was designed to allow a higher rate of evaporation from within the centre of the substrate (in your case solid brickwork)
Please don't be confused by the purpose of this system, the system is designed to combat the effects of rising dampness and not to increase sub-floor ventilation as the vents are only inserted into the centre-3/4 of the wall and not completely through it.
If it's to increase sub floor ventilation, then Welsh Brickie is correct, install air bricks below the internal timber wall plate. I recommend, installing a minimum of 2 9x3" bricks per elevation (side) to reduce the risk of sub floor humidity buildup which can lead to defects such as wet rot, dry rot and insect infestation. Basically you want to achieve 1 air change per hour.
If you want to stop rising dampness, get a new DPC installed, this can be either physical or chemical. This will form a barrier to any rising moisture using capillary action through the brickwork.
The Dutch system relies on moisture evaporating from the masonry before it becomes a problem but the amount of evaporation achieved is minimal and as such has been removed from common practice.