A TV antenna mast is a steel pipe that passes through your roof, and every one of those penetrations is a place where the flashing has to shed water. When a homeowner in St. Louis sees a stain near the living room ceiling or a damp patch on the attic side of a rafter, the antenna is often the last thing anyone checks. The mast gets blamed for the stain while the shingles nearest it get no attention at all. This page explains where a mast leak usually starts, what you can check yourself from inside the house, and what to ask for before anyone climbs up to fix it.
Leak and repair
Most antenna masts reach the roof through a base plate or a flashing collar that sits over the shingles and is fastened to the roof deck. The pipe then runs up through the attic, where it is braced to the rafters or blocked at the ceiling. Water can enter at the base in three common ways. The fasteners through the base plate can sit in the shingle courses, and each nail hole is a path if the nail backs out or the shingle above it lifts. The collar can have a sealant bead that dried, cracked and pulled off the pipe in the first cold snap. Or the shingles uphill of the mast can have been cut to fit around the base, leaving the top edge of the cut exposed so water runs under the shingle and down onto the plate.
The uphill side is where the trouble usually starts. Rain runs down the roof and hits the upslope edge of the base first. If the flashing has a seam or a gap there, water goes under the plate and into the penetration, then tracks down the outside of the pipe into the attic. Because it follows the pipe, the stain often appears well away from the mast, sometimes several feet down the ceiling, where the water finally drips off the pipe or runs along a rafter.
Wind makes this worse over time. A mast is a long lever. Each gust rocks the pipe against the base, and the nails and the collar work loose a little more with every storm. Guy wires add a second load. Many masts are held by wires anchored to the fascia, the roof edge or a stand-off bracket, and when those anchors pull, the fascia can lift and the flashing around the mast can separate. Ice adds weight in winter, and the freeze and thaw cycle that St. Louis gets every winter opens sealant joints that were marginal to begin with.
You can narrow the source from the attic before you ever get on the ladder. Take a flashlight and look at the pipe where it enters the roof space. Look for a dark ring on the roof deck around the pipe, rust or staining on the pipe, soft or darkened sheathing, and daylight around the penetration if you can see it from the outside. Check the rafters on the side of the pipe that faces uphill, because that side takes the water. If the stain on the ceiling is on the far side of the room, follow the pipe with your eye back to where the wet line starts. The point where the staining begins is usually a good guide to where the water got in.
From the ground, look at the mast for loose or bent sections, a wire that has pulled off its anchor, and sealant that has split. Do not climb the mast and do not hang on the guy wires. A mast under load can shift, and a guy wire under tension can snap. If the mast is wobbling, the base is not the only problem.
Hail also reaches masts. A dented base plate or a bent collar can open a seam that was tight before the storm. Photograph the mast and base from several angles before any work starts, and note the storm date if there was one. A written scope with photos is the record that protects you if the damage later turns out to be storm-related.
Once the source is found, the repair is usually one of three things. The base can be reflashed with a new collar sized to the pipe, with the shingles around it re-laid so the uphill course laps over the flashing. The guy anchors can be moved to solid framing or fitted with stand-off brackets and new flashing at each fastener. Or the mast can come down, the penetration can be closed with a properly flashed block, and the antenna can be relocated. Caulk alone is rarely the answer. A bead of sealant can hold for a season, and then the stain comes back under it, which is the same pattern homeowners see with other penetrations.
What it costs
The price of a mast repair depends on what has to be taken apart to reach the base. Reflashing one base in a simple shingle field is a small job. Removing and resetting a long mast, re-running the guy wires, repairing the fascia where an anchor pulled, and re-laying shingles across a wide area add labor and material. If the mast belongs to a cable or satellite provider or to a separate antenna company, the removal and reinstall of their equipment may need to be scheduled through them, and that time can change the date of the roof work.
Ask whether the quote includes the mast itself or only the flashing under it. A quote that treats the mast as an obstacle to work around will leave the pipe, the braces and the guy wires in place, and those are the parts that moved in the first place. Ask whether the wires get new anchors and new flashing at each fastener, or whether the old anchors are simply retightened. Retightening an anchor that has pulled through the fascia does not fix the fascia.
If the roof is also due for replacement, the mast should be addressed in that scope rather than as a separate patch. Shingles removed around the base are a chance to set a proper collar, but only if the bid says so. The mast and its flashing belong on the same line as the rest of the penetrations, not in a general repair allowance.
What to ask
- Will the mast be removed and reset, or will the base be reflashed where it stands? Ask what happens to the pipe, the braces and the guy wires in each case.
- Who is responsible for the antenna equipment and its removal? If a provider or antenna company must come out, ask who schedules that and how it affects the roof date.
- How will each guy wire anchor be flashed, and will the fascia or stand-off bracket be inspected where a wire has pulled?
- Will the shingle course above the base be re-laid so it laps over the new flashing, and will the cut edges be sealed?
- Will photographs be taken before and after, with the mast, the base and each anchor shown?
- What is the scope of any attic work, such as replacing stained sheathing around the pipe?
Get the answers in writing before work begins. A written scope with photos and measurements is what Keys Roofing puts in the homeowner's hands, and it is the document to compare against any other bid. If you have a question about the mast or the roof, call the Keys office at (314) 220-2333 and ask for the scope to be written before the crew arrives.
If an insurance claim is involved because of storm damage, Missouri law (RSMo 407.725) forbids a roofing contractor from representing or negotiating that claim for you, and from saying anything about paying or covering a deductible. Keys documents the damage, supplies the written scope and photographs, and attends as the contractor while you deal with your own insurer.