Ventilation plays a key role in keeping mould and mildew out of your home. Having adequate cross flow ventilation in your sub-floor helps prevent, cure or reduce timber decay, cupping of floor boards, and risk of termite attack. Aleta Vents also allow natural light into your sub-floor making it less desirable for termites and other nasties. The 390x190mm vent (Besser Block size) give 17,400 sq mm of ventilation per vent.