A roof leak rarely drips straight down from the spot where water gets in. Water that slips past a shingle, a pipe boot or a piece of flashing usually runs along the roof deck or a rafter first and lands on the ceiling somewhere downhill, so the stain tells you there is a roof leak but not where it is. On Central Texas homes, finding the real entry point is most of the work of a lasting roof leak repair.
Why isn’t the stain right under the leak?
Water inside a roof follows the wood, not gravity alone. Once it gets under the shingles, it runs down the underside of the decking or along a rafter until it reaches a low point, a nail or a gap, and drops onto the insulation and ceiling there. InterNACHI, the home inspectors’ association, notes that water stains on the underside of roof decking show past and present leaks even when nothing has reached the ceiling yet.
That is why a stain in a hallway can trace back to a vent pipe over a bedroom, and why patching the shingles directly above a stain so often fails to stop it. The attic usually holds the trail.
Where do most roof leaks actually start?
Most roof leaks start where the roof is interrupted, not in the open field of shingles. The 2012 International Residential Code, which Texas law adopts as its residential code, requires flashing at wall and roof intersections, wherever the roof changes slope or direction, and around every roof opening under Section R903.2. Those are the places a roofer checks first, because they are the places a code had to address.
- Pipe boots. InterNACHI’s roof inspection guidance says the rubber or plastic boot that seals a plumbing vent dries out, cracks and leaks as it ages, and is sometimes missing entirely. A cracked boot is one of the most common leaks we find on otherwise sound roofs.
- Walls and chimneys. The code calls for step or continuous flashing at least 4 inches tall and 4 inches wide where a roof meets a sidewall, a flashing that diverts water where an eave runs into a wall, and a cricket on the uphill side of any chimney wider than 30 inches.
- Valleys. A valley collects water from two roof planes. The code requires the valley lining to go down before the shingles, and an open metal valley lining to be at least 24 inches wide.
- Nails. The code requires at least four nails per strip shingle, driven at least 3/4 inch into the sheathing. A nail that backs out lifts the shingle above it and opens a path for water.
- The roof edge. Shingle roofs need a drip edge at eaves and gables that extends at least 0.25 inch below the sheathing. A missing or bent drip edge lets water wick back onto the decking and fascia.
Is it a roof leak or attic condensation?
Some ceiling stains are not roof leaks at all but condensation forming inside the attic. The Department of Energy’s Building America program explains that in cold weather, warm, moist air escaping from the house or from attic ductwork can condense on the trusses and the underside of the roof sheathing. InterNACHI adds that when attic ventilation fails to move moist air out through the ridge and fresh air in through the soffits, moisture builds up in the attic.
The pattern gives it away. A leak shows up after rain and tracks back to one point. Condensation shows up on cold mornings, spreads across wide areas of decking, and often leaves rusty nail tips, which InterNACHI says point to a moisture problem that has been going on for a while.
Could the water be coming from the air conditioner?
In a lot of Central Texas homes the air handler and ducts sit in the attic, so a wet ceiling in summer is worth checking against the AC before anyone blames the roof. ENERGY STAR’s maintenance checklist says a plugged condensate drain can cause water damage in the house. Building America’s guidance on ducts in attic insulation calls for sealing them in closed-cell foam in humid climates because of condensation concerns.
A stain that grows on a dry, hot week, sits near a supply vent or the air handler, and does not change after rain points to the AC side. That is a job for your HVAC company, and we will say so if that is what we find.
What should you do about a ceiling stain today?
Dry what you can and get the source found quickly, because mold follows water. The EPA’s guide to mold and moisture says water-damaged areas and items should be dried within 24 to 48 hours to prevent mold growth, and that no mold grows without moisture. The EPA’s cleanup guidance adds that porous materials such as ceiling tiles and carpet may have to be thrown away once they become moldy.
From inside the house, put a bucket under any drip, move belongings out of the way, and take photos of the stain with the date so you can see whether it grows after the next rain. Leave the roof itself to someone with the right equipment.
What we check when we trace a leak
We start in the attic when there is access, follow the water trail on the decking and rafters back uphill, and then match it to what is on the roof above: the boot, the flashing, the valley or the nail that let it in. We photograph what we find on both sides so you can see the path for yourself. If the trail leads to condensation or to the air conditioner, we tell you that instead of selling you roof work.
Most leaks are a contained roof repair: a new pipe boot, a reset run of step flashing, a reworked valley. The National Roofing Contractors Association recommends a roof inspection twice yearly, in spring and fall, and after any severe storm, which is also the easiest way to catch a cracked boot before it reaches the ceiling. If you have a stain you cannot explain in Liberty Hill, Georgetown, Leander or Cedar Park, book a look here and we will find where it is coming from.