Whether you're adding a room, installing new carpet, or painting, you're putting yourself and family members in potential harm's way if you don't have a mitigation plan for off-gassing, dust, and other pollutants. Sealing up the room you're remodeling to keep particulates from invading the rest of your home is a crucial step that too many people avoid taking.
Indoor air quality depends on totally sealing off the room, not in just hanging a sheet of plastic over the doorway. For one thing, every time you open the flap, you're exposing the rest of your home to dust, chemicals, volatile chemicals, and inhalants. That's why you need at least a double door of 6 millimeter plastic--like an air lock--where you enter and exit the work space.
You should doggedly seal any unnecessary openings around wiring or pipes that run down into lower floors or crawlspaces. Mold, moisture, radon, allergens, volatile organic compounds, and pesticides can waft into your home through these causeways. Temporary seal any duct work into the space. Put towels or old blankets into the ducts until you're done.
Wear a genuine dust mask, not a cheap painting mask. Even better, find a particulate mask at your home improvement store and wear it! At the same time, make sure your workspace is well ventilated to the outdoors, rather than into other areas of the home. You can use an exhaust fan to draw gasses and particulates out of the house, but be sure to seal the lip around the window or funneling you use to create a good out-venting seal.
EPA-Suggested Air Quality Tips
The Environmental Protection Agency suggests that you always keep your building materials dry. Insulation, fabric, wood, and paper can become a breeding ground for bacteria and mold if it gets wet and stays that way. If your materials arrive wet, dry them out within 24 hours or ship them back.
Air quality during renovation, along with work safety, should be your main considerations. If you're installing new carpeting or paint, give the room 72 hours to vent out an open window before occupying the space. Floor adhesives, cleaning chemicals, caulk, sealants, and other materials come with health warning labels, and you should exceed any suggested measures.
Clean up your spills immediately, rather than letting them seep into a drop cloth--or replace the drop cloth if necessary. Work safely!