False.
I often read and hear people, including passivhaus experts, state that once a building is airtight it requires mechanical ventilation. This is not strictly true. And there are many examples of passivhaus buildings that operate using ‘natural ventilation’ during the summer months. An airtight building significantly reduces air movement through the building fabric: walls, floor, roof, window frames and junctions etc.. And we should never rely on this kind of air movement to provide the air that we breath inside a building, for ventilation, that is. (Fancy drinking the water that seeps through a leaking roof? It’s kind of similar.) A ventilation strategy and system that genuinely does work, and is used properly all year round, is needed in any building, airtight or not. Once you add comfort and energy efficiency into the equation, this almost always means mechanical ventilation with heat recovery will be required for some of the year. The comfort and energy efficiency benchmarks of the Passivhaus Standard certainly mean this is the case.
And this is where airtightness and mechanical ventilation converge – both are needed for comfort and energy efficiency.
