There is a lot of talk about sick building syndrome, with blame being placed on various things, including building tightly sealed houses.  It is true that old houses tend not to have the problem because they're inundated with fresh air, but they're also drafty and expensive to heat.  A better idea is to prevent toxins in the first place.

There are just a few key principles to remember:

• Keep rain and groundwater out.
• Keep relative humidity in the 30-60% range
• Avoid using toxic glues, caulks, paints, sealers, wood products etc.
• Avoid using toxic cleaners, pesticides, herbicides etc.
• Make sure you have adequate ventilation

There are known construction techniques to deal with water and condensation, and local building codes will typically require that at least some of them be followed.  Unfortunately when a house is sealed tight, the humidity can go up causing condensation, so extra caution must be taken to deal with this. This is covered in detail in the health section of the tutorial.   Virtually all construction adhesives, caulks, paints etc have a non or lower toxic alternative.

Adequate ventilation is a more difficult topic because the amount is driven mostly by the need to dilute pollutants, including the carbon dioxide we exhale and the various other pollutants we use or create.  The recommended minimum amount is 15CFM per person.

Unfortunately, unless you're doing extensive filtering, indoor air is always dirtier than outdoor air because the air doesn't magically get any cleaner whether its coming through your windows or leaking through your walls.  In good weather you can keep your windows open.  Filtration also works, but it can be a significant energy user.

To us, health includes mental health, so we see a house as much more than a box that keeps you warm and dry.  The layout needs to support the family's activities, not interfere with them.  It has to support interaction as well as privacy.  People like to be able to sit in the sun, the like to be able to sit and look outdoors, they like to feel protected.  There is a lot more about this in the design section.

If your lifestyle isn't that healthy you might not be inclined to care about any of this, but in fact you probably should care even more since your body has less reserve to fight off toxins.  Children are the most vulnerable.