insulation, vapor barriers and moisture

We need humidity in the air we breathe, but too much moisture is a cause of damages in the building materials and a source of health problems. Uncontrolled moisture can lead to mold growth.

Keeping Moisture away

When moist air comes into contact with cold surfaces, part of the air vapour condenses, which may happen inside a wall or in the attic, away of our seeing, causing the problems.

Assuring the integrity of exterior walls through insulation is the first line of defense for preventing moisture. But it is not sufficient: a correct insulation of interior walls, basements, attics, roof and ceiling are also essential means for keeping moisture away.

The Right insulation materials

You should ponder the best materials to prevent moisture. Good water resistant wall paint is a very effective and easy way of preventing moisture and a first insulation barrier. But there are other more specific materials, namely:

- polythene sheets
- reflective foils
- foil backed plasterboards
- polystyrene (see: Spray-on foam insulation)

Materials with a vapor-barrier membrane are particularly suited for more extreme situations: the membrane decreases the possibility of moisture vapor condensing to water within walls, attics or other structures. Common examples is asphalt impregnated paper and metal foil.

Vapor barriers

Vapor barriers are an intrinsic part of many insulation products. Floors, framed walls or roofs should have vapor barriers on the warm, moist side of the insulation.

In case of floor slabs contacting with the ground, consider installing a 3-6 mil continuous vapor barrier under the slab. It's essential to prevent moisture to seep in.

Correctly installing a vapor barrier

Tape or glue the vapour barriers joints. Ensure that vapor barriers are continuous, not damaged and tightly secured.

Use vapour barriers to protect materials from condensation wherever needed, namely in places with low ventilation and on underside of metal roofs. Vapor barriers are specially important in lockers, showers and other areas of the house where the humidity levels are usually high.

Other ways of controlling moisture

Insulation is important, but there are other structural approaches that should be implemented, involving areas like the windows, doors, roof flashing and other areas where moisture can easily enter into the building.

Pay also attention to the drainage issue: adequate sloped roofs, sloped intake plenum, adequate ground slope around the building, sufficient overhang in exterior entries, well cleared and opened gutters and downspouts, are important areas that should be considered. See: Drainage issues.

Another major way of fighting moisture is natural and mechanical ventilation. An adequate ventilation of spaces where moisture can build up is crucial, and there are building codes requiring and defining ventilation in crawl spaces, attics and vaulted ceilings. But, be careful... Ventilation can also be a cause of condensation and… moisture in our homes. Excessive ventilation in humid (cold or tropical climates) is a cause of undesired moisture.