Is my ceiling stain a roof leak or a plumbing leak?

EPA lists the usual suspects together. Its list of common moisture problems includes "Leaking roofs" and "Leaking or condensing water pipes, especially pipes inside wall cavities or pipe chases." In other words, both are ordinary, and neither is rare enough to assume.

The location of the stain is also unreliable. Water travels along framing, ductwork and insulation before it soaks through drywall, so the wet spot on your ceiling can sit several feet from the entry point. That's true for roof leaks and pipe leaks. Use the stain as the starting point of a search, not the answer.

Work through these in order. The first two cost nothing, and the last two confirm what they suggest.

### Clue 1: timing

Timing is the most useful clue, and it costs nothing to check. Keep a simple note for a few days: the date, the weather and what was running.

• The stain grows during or after rain. That points to the roof. In Phoenix, that often means monsoon storms, so a stain that only appears in July, August or September deserves a roof check first.
• The stain grows when water is used upstairs. A shower, a washing machine cycle or a flush, followed by a drip, points to a drain line or fixture above.
• The stain grows on dry days and doesn't care about rain or water use. A supply line is always under pressure, so a leak there runs around the clock. A stain that also grows on dry, sunny days is a strong sign of plumbing.
• The stain grows on the hottest days and stops when the A/C is off. That points to the condensate line or a sweating duct. See air conditioner condensate drain rules for how that drain is supposed to work.

### Clue 2: what the stain looks like

Rainwater stains tend to show a brown ring, sometimes with fainter rings outside it, and the surface may be stained but not sagging. Plumbing leaks are more likely to leave a spot that stays soft or bulges, because a steady leak keeps the drywall wet. A stain near a bathroom, kitchen, laundry room or water heater is a plumbing candidate. A stain along an exterior wall or under a roof valley is a roof candidate. These are tendencies, not rules.

### Clue 3: the attic

If you can get into the attic safely, look directly above the stain. Go in the early morning when it's coolest, stay on the framing, and use a flashlight. Signs of a roof leak include damp or dark roof decking above the stain, water trails down rafters and daylight where it shouldn't be. Signs of a plumbing leak include a wet pipe or fitting, a dripping shutoff valve, or wet insulation around a supply line or a water heater. A leak from a sweating pipe or duct is a third possibility; why pipes sweat in summer shows how to tell condensation from a leak.

EPA notes that hidden problems collect in "roof materials above ceiling tiles (due to roof leaks or insufficient insulation)" and inside walls "around pipes (with leaking or condensing pipes)."

If you can't see a clear source, leave it and call someone.

### Clue 4: the meter test

This is the fastest way to rule plumbing in or out. Turn off every water-using fixture, the ice maker, the irrigation controller and the washer. Then watch the meter. EPA says: "Check your water meter before and after a two-hour period when no water is being used. If the meter changes at all, you probably have a leak."

• The meter moves. Water is escaping somewhere, and a supply-line leak above the ceiling is a real possibility. It could also be a leak elsewhere in the house, so a moving meter doesn't prove the stain is from plumbing.
• The meter is still, and the stain grew on a dry day. Plumbing under pressure is unlikely. Look at the condensate line, a sweating duct or a drain line that only leaks when used.
• The meter is still, and the stain grew after rain. Now you have two clues pointing to the roof.

Our page on how to do a water meter leak test covers digital and dial meters. For more on the hidden signs, see the hidden signs of a water leak.

Many Phoenix homes have the air handler in the attic, and the condensate drain runs from there. When that line clogs, the pan overflows and drops water onto the ceiling below. EPA's mold guide tells people to "Keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly." A condensate stain grows in the cooling season, usually on hot, humid days, and stops when the A/C is off. If you see water in the pan or a wet spot right below the air handler, tell whoever services your A/C.

The right trade depends on which pattern you matched, and calling the wrong one costs you a visit.

• Roof. A roof leak is a job for a licensed roofer. Arizona licenses roofing as its own class. The state's contractor rules describe the R-42 roofing class as one that "allows the licensee to apply, repair, or install weatherproofing" and "roof accessories (i.e. flashing, valleys, gravel stops, or sheet metal)." Ask any roofer for their license number and check it with the Registrar of Contractors before work starts.
• Plumbing. If the meter moves, the stain grows without rain, or the drip follows water use, that's plumbing. HQ Plumbing & Air can find the source with leak detection so the ceiling isn't opened blindly. We're licensed and insured, we give you a free estimate, and you get the price up front before work starts. If water is coming through and you can't stop it, we're available 24/7.
• A/C condensate. Start with whoever services your air conditioner.
• Not sure. Turn off the water at the main and watch the stain. If it keeps growing and the sky is clear, keep looking at plumbing. If it grows only when it rains, call a roofer.

Whatever the source, the wet drywall and insulation need attention. EPA says, "It is important to dry water-damaged areas and items within 24-48 hours to prevent mold growth." Roofers and plumbers fix the leak; neither fixes a damp ceiling cavity. Take photos of the stain and the source before you clean anything up, since your insurer may ask. Read how to file a water damage insurance claim before you call.

Here's the short version. Rain points to the roof. Water use points to plumbing. A meter that moves, or a stain that grows on a dry day, points to plumbing. A hot-weather stain points to the A/C line. Match the pattern, then call the right trade.