Where a roof meets a brick chimney or a brick wall, the flashing is built in two layers. The base flashing lies on the roof and turns up the masonry. The counterflashing is the metal that covers the top edge of that base layer, and its job is to keep wind-driven rain and snowmelt from getting behind the base. On most brick work in St. Louis the counterflashing sits in one of two ways: cut into a mortar joint in a slot called a reglet, or mounted on the surface with a bracket and a bead of sealant. The spec should say which one, what metal it is, how thick it is, how deep the reglet runs, and how far each piece laps the base. A quote that says only that the chimney will be flashed does not tell you any of those things.
Material and spec
Counterflashing is usually aluminum, galvanized steel, or copper. Aluminum is light and bends easily on the roof, but it is soft and shows dents from hail and from ladder hooks. Galvanized steel is stiffer and holds a straight line over a long run of brick. Copper lasts longer than either and costs more. The shingle name on the wrapper, whether it is an Atlas or a Malarkey product, does not cover this metal. The counterflashing is its own line in the spec, and it needs its own material name and gauge. A thin piece will flex under foot traffic and under the weight of snow sliding off the upper slope, and that flex is where the joint begins to open.
In St. Louis the freeze-thaw cycle does a lot of the damage. Water gets into a mortar joint during a wet spring, freezes in January, and pushes the joint apart as it expands. A counterflashing that is loose in its reglet lets that water in every winter. After a few seasons the joint is open, the base flashing is exposed to weather it was not built for, and the first sign is often a stain on a ceiling near the chimney chase, months after the water first got in. That is why the reglet depth and any mortar repair belong in the written spec and not in a note the crew reads on the day.
Reglet depth is the number most homeowners never see. A shallow slot holds the metal loosely and gives wind a way to lift the edge. The spec should state the depth, and the crew should cut the slot into sound mortar. The metal is then set in the joint and secured, and the joint is sealed with a product named in the spec. If the mortar crumbles when the slot is cut, the crew is looking at repointing, and that work should appear on the quote as its own line with a stated scope, not as a surprise halfway through the job.
Lap is the second number. Each piece of counterflashing should overlap the base flashing by a distance written into the spec, so that water running down the brick sheds onto the base and not behind it. On a chimney with a wide front and a narrow back, the back and the sides are where the overlap tends to get short, because those faces are hard to reach from the ladder. Ask the crew to photograph each lap before the mortar is patched, while the metal can still be seen. A lap photo is inexpensive evidence, and it is the kind of record that stays with the house after the crew leaves.
Surface-mounted counterflashing is a different spec. It is used where the brick cannot take a reglet, such as thin veneer or soft older brick, and it is also used as a repair when a reglet is not practical. Here the metal sits on the face of the masonry on brackets, with a sealant bead along the top edge. The sealant is part of the detail, so it needs a product name, not a generic description. The spec should also say how the crew expects the joint to hold up and when someone will return to check it, because sealant generally needs attention sooner than metal set in mortar.
Hail reaches counterflashing too, often more than people expect. Dents on the front face of the metal, and scrapes along the bottom edge where it meets the brick, belong in the photo file before the tear-off starts. St. Louis hail season runs through spring and into early summer, so a chimney that took a hit in April may not show the mark until someone looks closely at the metal in low light. Keys documents what is there, with photos and measurements, and puts that file in the homeowner's hands. What the homeowner does with it is a matter between the homeowner and their own insurer.
What it costs
Counterflashing is usually priced as its own line in a roof bid, by the linear foot of run or by the count of chimney and wall terminations. The number depends on the metal, the length of the run, whether the crew cuts a reglet or mounts the metal on the surface, and whether the old mortar needs work before the metal can go in. Copper will cost more than galvanized for the same run. A reglet cut into hard, dense mortar takes more time than one cut into soft joints. If your quote folds the counterflashing into a general flashing allowance, ask for that figure to be pulled out so you can compare it line by line with the next bid.
Repointing is the item that moves the total the most. If the crew cuts the slot and the joint breaks apart, the job grows, and that growth should come through a written change order before anyone touches the mortar. Ask whether repointing is in the bid, how deep the repointing goes, and what mortar mix will be used. A mortar that is harder than the old brick can crack the brick over time, and that is a masonry problem that shows up later as a roof problem. The mix should match the age and hardness of the masonry, and the spec should say so.
Some crews fabricate counterflashing on site from a coil, and others bring pre-formed pieces to the job. Either method can produce a good result, but the spec should say which one is being used. A pre-formed piece that does not match the actual width of the chimney becomes a re-cut on the roof, and a re-cut on the roof is where the lap usually gets shorter. Ask how the metal will be sized to the chimney, and whether the crew measures the masonry before the metal is ordered rather than after.
Missouri does not license roofers, so no state table sets the price of counterflashing. The comparison is made on the written scope. Two bids that name the same metal, the same gauge, the same reglet depth, the same lap, and the same repointing scope can be compared directly. Two bids that name none of those things cannot be compared at all, whatever their totals say.
What to ask
- What metal is named for the counterflashing, and what gauge or thickness is written into the scope?
- Will the counterflashing sit in a reglet cut into the mortar, or on the surface with brackets and sealant?
- How deep is the reglet, and will the crew cut into sound mortar or set the metal over the old joint?
- How far does each piece lap the base flashing, and does the lap run over the step flashing on the slope?
- Is repointing included in the bid, and what triggers a written change order before the mortar is touched?
- Will the crew photograph the existing counterflashing, with a tape in frame, before any metal comes off?
- Which sealant is named for any surface-mounted pieces, and who returns to check the joint after the first winter?
If the answers arrive in writing, you have a spec you can compare. If they arrive as a general assurance, finish that conversation before you sign. Keys Roofing can be reached at (314) 220-2333 to walk through the chimney or wall you are deciding about, and the written scope will carry the counterflashing detail along with the rest of the roof.