Home Insulation materials and House Moisture

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Insulation & 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 that impairs indoor air quality.

When moist air comes in contact with cold surfaces, part of the air vapour condenses, which may happen inside a wall or in attics, 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 a correct insulation of interior walls, basements, attics, roof and ceiling are also essential means for keeping moisture away.

Right insulation materials to prevent moisture problems

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 the more exigent cases of insulation: the membrane decreases the possibility of moisture vapour condensing to water within walls, attics or other structures. Common examples is asphalt impregnated paper or metal foil.

Vapor barriers

Vapor barriers are available as part of many insulation products, and are a crucial way of keeping moisture out of buildings. Floors, framed walls or roofs should have vapor barriers on the warm, moist side of the insulation.

For floor slabs contacting with the ground, you should consider installing a 3-6 mil continuous vapor barrier under the slab. It's essential to prevent moisture entry through it.

Correctly installing a vapor barrier

Use vapour barriers to protect materials from condensation wherever needed: in places with low ventilation, 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.

Also tape or glue joints in vapour barriers, and during construction ensure that vapor barriers are continuous, not damaged and tightly secured.

Other ways of controlling moisture

Insulation is important, but the design and proper installation of roof flashing, windows, doors and other areas where moisture can easily enter the building are also crucial.

Also crucial are drainage measures linked to the house: adequate sloped roofs, sloped intake plenum, adequate ground slope around the building, sufficient overhang in exterior entries, well cleared and opened gutters and downspouts, etc.

Another major way of fighting moisture is ventilation. An adequate ventilation of spaces where moisture can build up is fundamental, and there are building codes requiring ventilation of crawl spaces, attics and vaulted ceilings.

But ventilation should also be managed carefully, because it can also be a cause of condensation and… moisture in our houses. Excessive ventilation in humid (cold or tropical climates) is a cause of undesired moisture.

See for more information:
Natural ventilation
ERV and HRV ventilation