Prevent Mold

Mold occurs everywhere there is cellulose (eg wood) because it's job in the ecosystem is to break it down and recycle it's nutrients.  We prevent mold by taking away what it needs to grow, which is water.  This means keeping rainwater out, keeping groundwater out, and keeping the humidity below about 60%.  If there was one simple rule about mold, it would be "keep wood away from the ground".  For a more detailed discussion click here.

Building codes do make an attempt to force builders to deal with water problems, but building codes are for safety, so in general they cover only the most dangerous situations.  Additional steps to consider are:

1. Make sure the entire foundation is isolated from the ground, via gravel drains, waterproofing, and a drain membrane.  Click here for an example construction detail.
2. In damp climates, use a "rain screen" behind our siding that helps prevent wind driven rain from getting it while also providing an escape for any excess house moisture.  Click here for example photos.
3. Use extensive flashing and a drain pan underneath all the windows. 
4. Provided for both natural and mechanical ventilation to reduce excess indoor moisture.

This is really an ongoing process, because once the home is complete you have to avoid bringing toxics in (which can come via furniture, cleaners, pesticides, office equipment etc).  For a more detailed discussion, click here.  In terms of building materials, the two worst offenders are interior grade particle board and carpet padding.   In general carpet isn't recommended because it acts as a sponge for toxics and dust (alas it releases them also), and a breeding ground for dust mites. Low or zero VOC paints and finished are now readily available, although low VOC doesn't necessarily mean low toxic, because there still can be toxins that don't readily evaporate.

We used hardwood floors, cork and linoleum for floor, low VOC paint from various fairly reputable manufactures, and some low VOC clear finishes (and some that aren't).  The contractor uses low VOC construction adhesive and caulks.  We avoided interior grade particle board, and the only particle board cabinets are from IKEA, whose cabinets meet strict European VOC standards.

Careful placement of opening windows to take advantage of summer breezes reduces cooling load, and for taller houses, a pathway for air from bottom top is very effective at removing hot air during cooler nights. Even a very tight house still leaks quite a bit of air, and that amount is much greater during cold, windy days than it is on moderate days.   While it would take extraordinary effort to build a house that didn't leak enough air to provide the necessary replacement oxygen, ventilation air is also necessary to dilute unwanted things in the air: excess moisture, odors and toxins (more...). In a tight house, using spot ventilation (kitchen and bath fans) is necessary if the windows aren't open.  Low power, very quite fans are available (panasonic, for example).

Whole house fans can provide large quantities of fresh air and can also provide air filtration, although use much more power than spot ventilation fans.