Before you call anyone, do some research on your own. Once you understand the cause of the water stains, you may also find that the solution is something you can handle yourself. If you do need to hire a pro, you'll be more certain of which type of firm to call.

Don't try to fix the stain or any damaged drywall or plaster until you're sure you have the moisture problem solved. When you're sure you've solved the problem, repair the walls and ceilings, but make sure you use a stain-killer primer before repainting. Otherwise, you may find the stain bleeds through the new paint.

Here are some common questions about ceiling water stains:

Q: I have a stain on my living room ceiling. The ceiling is directly beneath an upstairs shower. I re-caulked the shower, and the problem is still there. Do I need a plumber to replace the pan under the shower?

A: Probably not. You were correct to suspect the caulking. It is usually the culprit. However, simply adding another layer of caulk over the old caulk usually does little good. Instead, you must remove the old caulk completely, clean and dry the surfaces and then recaulk.

Q: This past winter, we had problems with leaks during the snow. We have never had leaks during rainstorms. Should we have a roofer check the roof before we repair our ceiling?

A: You should call a roofer first. Unless your roof is getting old, there is probably no problem with the roof itself. You probably have an ice dam problem. The roofer can check your insulation in the attic and investigate ways to improve air circulation. If you try to take advantage of a roofer's expertise without paying for his or her time, you will probably get an incomplete investigation and inadequate advice. If you explain up front that you will pay for the time it takes to really figure out the cause and appropriate solutions, you will get a much more fully thought-out diagnosis and solution.

Q: On the coldest winter days, my attic is completely covered with what looks like frost. What should or could I do about it?

A: You should solve the problem before it causes rotting, mildew, infestations and other serious problems. Warm, moisture-laden air is escaping from your home into the attic. When this air encounters the cold surfaces in the attic, water condenses onto the surfaces in the same way that water condenses on the outside of your ice tea glass in summer. If it's cold enough, the water then freezes.

To solve the problem, you have to identify and reduce the source of moisture or improve your attic's ventilation. Moisture typically comes from bathroom and kitchen fans that exhaust to the attic rather than to the outdoors. If that is the problem, reroute the exhaust ducts. If that isn't the problem, you probably have air leaking up from heated spaces below. Look for openings around light fixtures or entrances to the attic. Use weather stripping or insulation to reduce this air flow. To improve attic ventilation, make sure all attic vents, especially ones near the soffits (also called overhangs or eaves), are unobstructed by debris or insulation. A roofer can help you explore other ways to improve ventilation.

Q: My dad always told me to shellac over a stain before repainting. Is that still necessary?

A: Water stains will typically bleed or seep through new coats of paint. To prevent this, shellac or a special kind of primer must be applied before painting. This special primer is appropriately called "stain-killer" primer. Regular primer won't work.

Q: One pipe under my sink is always wet. Water drips from it onto the floor and has left a stain on the ceiling below. Should I call a plumber?

A: Check to see if the pipe is wet all over or just below a seam. If it's wet all over, the problem can be solved by insulating the pipe. This is an easy do-it-yourself project. Your local hardware store or home center can help you identify the right insulating product to use. If the moisture shows up just below a seam, you probably have a leak and should call a plumber.

Q: I have a stain on the ceiling of a front bedroom. My roofer says it was caused by a problem with the flashing on my chimney 15 feet away. Am I being taken for a ride?

A: If you are working with a reputable roofer, he's probably dealing straight. It is not uncommon for water to run along rafters, pipes, ducts or wires for long distances before dropping down to create a visible stain on a ceiling below.

by David Hollies, reprinted courtesy of HomeAdvisor.com