Foundations are a common source of moisture problems in living areas.
Foundation Moisture Problems in New Homes
Many brand new homes have moisture issues in and around their foundation; and you should be aware to it, if your are going to build a new home.
When building a new home, consider carefully the best type of foundation: crawlspace, concrete basement, slab, pier foundations. Make sure that the type of foundation you are considering is suitable for areas prone to flooding or with wet soils, if that is your case. Avoid basement and crawlspace foundations in areas with wet soils. That's a basic rule.
The other key factors for a dry foundation is an adequate outdoor drainage and a highly effective foundation waterproofing (including capillary breaks: an elastomeric paint, at the foundation footing; and gravel and a thick polyethylene sheet, properly sealed). Withouht it, water in soils or around the foundation, or in the foundation itself, can move a long distance upwards, and be a cause of structural moisture problems.
Foundations should be carefully waterproofed - which is easy and relatively inexpensive to achieve in new construction; proper sealing – including the sealing of the edges of the slabs – and proper surface drainage (including deep overhangs) and under-ground drainage (using lots of gravel) are critical to prevent future moisture problems.
Moisture in Basements/Crawlspaces
Basement moisture can cause unhealthy indoor air and higher energy bills.
In the summer, air conditioners will have to run longer, to deal with moist air. And in the winter, the air that it warmed by your heating equipment will cause excess moisture to evaporate, cooling the air, which in turn requires more heating.
Foundation Moisture Problems in Existing Homes
As expected, foundation moisture problems are a lot more complicated do deal with in existing homes, though you should try hard to solve them.
It's your home’s structures and your health that are at stake (mold and mildew are a source of many health hazards).
In more severe cases you will need to redesign the surface and the under-ground drainage system of your home; in less severe moisture problems, consider…
1) covering the ground of your basement or crawl space with a ground vapor barrier;
2) increasing the ventilation levels of your basement/crawl space;
3) sealing the basement walls.
Covering the ground with a polyethylene sheet
If you have a dirt-floored basement or crawlspace, consider covering its ground with a proper moisture-barrier sheet. It solves many moisture problems and helps control ground gases, radon and other ground pollutants.
Avoid heavy plastic sheets; prefer reinforced high-density polyethylene sheets. It's more effective, durable and tear-resistant.
Installation is easy. Just do not forget to seal the hedges to the foundation, using butyl or polyurethane - and also to seal the seams with a proper acrylic tape.
Increasing ventilation levels
Air movement throughout a basement or crawl space can help solve minor moisture problems. Whenever weather conditions allow, open up every access point to the basement, for outside dry air.
In some few cases, vents may also help. The amount of venting area for basements and crawlspaces varies with the type of climate. A document from the Michigan State Extension recommends 1 sq foot of vent area (with louvers or screens) for every 750 square feet of floor area covered with a polyethylene sheet.
Be aware anyway: ventilation is just a way of minimizing moisture problems in existing basements and crawlspaces, poorly designed. Modern approaches rely on tight basements (or other types of foundation), based on good design, waterproofing and drainage. Pay special attention to drainage...
Sealing and insulating the basement walls
Basement wall insulation – using rigid foam sheets all over the surface of the walls - can solve some condensation problems. The idea is to raise the temperature of the inside surface of the walls, to prevent condensation.
Obviously, that will not solve deeper problems and should not be undertaken without solving them first. Otherwise, it will only mask the problem for a while.