We all have heard of horror stories about homes that are rotting because of moisture trapped inside their walls and ceilings - something that is often associated with airtightness.
Old common sense supports the misconception about the relationship between airtightness and moisture problems and poor indoor air quality.
Many people, in cold climates, still think that houses need to “breathe”, which makes little sense and contradicts modern construction concepts.
In cold climates...
Houses do not need to "breathe";
They have to be airtight to avoid moisture and to be energy efficient.
Old homes and moisture
It’s true that many older homes do not suffer from big moisture problems.
Most of these buildings have very little insulation and very low levels of air-sealing, and water vapor flows through their walls and ceilings without causing rotting or mildew. But so do heat… These homes require very high levels of energy to be comfortable. They are were energy-wasters.
Besides, air leakage through walls, ceilings or other parts of the house is not a true solution for moisture problems.
We shouldn’t forget that the presence of moisture in the walls or ceilings can also be caused by air leakage.
Moisture often piggybacks on air, and condenses into water in the interior of ceilings and walls, when it encounters a cold surface. In other words: air leakage is a common cause of wall- and ceiling-rot.
Modern buildings should be tightly built.
Air leakage and indoor air quality
Many average homes still rely on air leaks to get outside fresh air. But that’s not a good or healthy approach.
Air leakage is a very questionable source of fresh air, to say the least.
Wall cavities, and openings in crawlspaces and basements are full of pollutants like formaldehyde, insulation particles, radon and many other dozens of chemical pollutants. And air leakage becomes a way of bringing them into the living space.
Air leakage can't provide sufficient fresh air or dilute pollutants in cavities, basements and crawlspaces.
Airtight homes require some sort of mechanical ventilation.
Air leakage cannot ever provide good ventilation and healthy fresh air. It provides over-ventilation of the house during harsh weather; and under-ventilation during the mild weather periods.
Air leakage and energy waste
Anyway, air leakage has other very negative effects, especially energy waste and unhealthy air… And this also a great reason to build tight.
Without a continuous and comprehensive air barrier, the insulation in the walls, floors and ceilings will not perform properly; air movement through building cavities with insulation materials such as fiberglass can reduce the efficiency of the insulation by as much as 40% or 50%.
In other words: moisture is a complex issue, and its sources and mechanisms have to be properly addressed; but that doesn't mean – in most climates, and namely in colder ones, where moisture is more likely to become an issue – that the house has to “breath”.
Moisture problems have to be solved through new construction methods, large supported by airtightness, air sealing and insulation.