The reason why so many people design their homes with basements or crawlspaces instead of concrete slab-on-grade foundations has more to do with habit than with advantages.
Basements & New homes
If you are going to build a new home think twice before building a basement (or a crawlspace). Getting more space to store stuff is rarely the true reason, as long as you can create space above the ground (which is often possible).
Do not forget that above-grade space is healthier and often cheaper and without the problems of underground spaces.
If you have decided to build a basement (or a crawlspace) do it right. Do not try to save money by not sealing, waterproofing or insulating carefully.
It's not easy, or common to build dry basements. But it's possible through careful sealing, waterproofing and insulation. Basements and crawlspaces can and should be built to provide healthy-dry storage space.
Basement Air Leaks & Energy Improvements
Pay attention to air leaks. They can cost you thousands of dollars in heating and cooling bills over the years.
During the heating season, for each cubic feet of hot air leaking out through the attic another cubic feet of cold air will enter your home through gaps and openings in the basement; and the same happens in the summer, though in reverse order.
Pay attention to cracks in the basement walls, and gaps around service penetrations (for telephone, electricity, TV, fuel, etc.); and check for air leaks in the floor system, between the first floor and the basement.
See: Basement Air Sealing
BASEMENT PROBLEMS AND THEIR RESOLUTION
Water seeping through walls, structural water problems. Resolution: foundation drainage and waterproofing.
Condensation, small moisture problems. Resolution: wall insulation, basement ground sealing; air sealing; ventilation;
Cold basements. Resolution: air sealing and wall insulation;
Heat losses or unwanted heat gains. Resolution: basement wall insulation.
Solving Basement Water Condensation Problems
Small condensation problems in your basement can be solved by insulating its walls (to make them warmer), by improving ventilation or by sealing air leaks.
However, none of these measures will solve structural foundation problems, involving water-saturated soils and wrongly designed drainage systems, or damaged basement walls.
Should you Insulate your Basement Walls? Should You Insulate the Floor Above the Basement?
Un-insulated basements are damp, cool and disagreeable.
Without proper levels of insulation, heat will flow through the walls and floors, increasing the heating (and the cooling) costs.
Why You Should Have a Good Drainage System
Many severe problems with basements are due to a poor drainage foundation system. If that is your case, you should repair and waterproof the exterior of the foundation walls, and install a proper drainage system.
Heating your Basement
Air seal and insulate your basement, before installing any heating system in it. That's important for comfort.
Do not insulate your basement without solving possible moisture issues, or without previously sealing air leakage paths.
Polystyrene and Polyethylene
Besides the typical caulks and air barriers used in air sealing, there are two materials that you should consider over more traditional ones: polystyrene (for basement walls) and polyethylene (for the ground).
Polystyrene is a water-resistant material, and can avoid many condensation and moisture problems, while polyethylene is an excellent moisture barrier sheet (see Basement Ground Covering).
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