# Roof Flashing: The Part Most Roofers Skip
If a roof leaks, the odds are it is not leaking through the middle of a shingle. It is leaking at a joint — where the roof meets a wall, a chimney, a vent or a valley. Roof flashing is the metal that seals those joints, and replacing it properly is the step that gets skipped more than any other on a re-roof. I have pulled up enough new-looking roofs over rusted, reused flashing to know it is not rare.
The short answer
Roof flashing is thin metal installed at every place the roof surface changes direction or meets something else: walls, chimneys, valleys, vents, skylights and eaves. It directs water back onto the shingles rather than into the joint. On a roof replacement, flashing should be replaced along with the shingles, not reused, because the flashing is usually the same age as the roof you are removing.
Key Takeaways
- Most roof leaks start at flashing, not at the shingle field.
- Reusing old flashing on a new roof is a common and quiet shortcut.
- Step flashing at walls has to be layered piece by piece — a continuous strip is a failure waiting to happen.
- Ask specifically whether flashing replacement is in the bid; it often is not.
- Correct flashing costs a fraction of what the resulting leak repair costs.
Where flashing goes and what each type does
| Location | Type of flashing | What it stops |
|---|---|---|
| Roof meets a vertical wall | Step flashing | Water running down the wall into the joint |
| Wall above a roof plane | Counter flashing | Water getting behind the step flashing |
| Valleys between two slopes | Valley flashing | High-volume runoff cutting under shingles |
| Chimneys | Base, step and counter flashing | Water tracking down the masonry |
| Pipes and vents | Pipe boot and collar | Water entering at the penetration |
| Roof edges | Drip edge | Water wicking back under the first shingle course |
The shortcut I see most often
Step flashing at a wall is meant to be installed as individual pieces, one per shingle course, each one lapped over the one below like scales. It is slower than the alternative, which is running one long continuous strip of metal up the joint and sealing it with caulk.
The long strip looks fine on day one. Then the sealant ages, the building moves slightly through Texas heat cycles, and water finds a path behind the metal with nothing beneath it to catch it. The leak shows up inside a wall, often far from where the water entered, and it gets diagnosed as everything except flashing.
The other one is reusing the old flashing. If a roof is being replaced because it is twenty years old, the flashing is also twenty years old. It has rust, fastener holes and bends from the original install. Putting new shingles over it saves a few hundred dollars on a job that will cost thousands to fix.
Why chimneys leak more than anything else
A chimney interrupts the roof on all four sides and is made of a material that moves differently to the roof deck. It needs base flashing at the front, step flashing up both sides, counter flashing set into the masonry, and often a cricket — a small peaked structure behind the chimney that splits water around it instead of letting it pool against the back wall.
Crickets are frequently omitted on wider chimneys because they take time and skill. If your chimney is more than about two feet wide across the slope and there is no cricket behind it, that back edge is holding water every time it rains.
What to ask before you sign
Ask one direct question: is flashing replacement included in this bid, and which flashings? A good contractor will list them — valleys, walls, chimney, pipe boots, drip edge. A bid that says “re-roof” and nothing else may or may not include any of it, and you will not find out until it leaks.
Pipe boots deserve their own mention. The rubber collar around plumbing vents is one of the cheapest parts on a roof and one of the first to fail from sun exposure. Replacing them during a re-roof costs very little. Leaving cracked ten-year-old boots under new shingles is a leak on a timer.
Shingle manufacturers publish detailed flashing requirements in their installation instructions, and installing outside those instructions can affect a materials warranty claim. GAF publishes its installation guidance publicly, which is worth a look if you want to see the standard your roof should be held to.
What it looks like when it is done right
New metal at every joint. Step flashing layered piece by piece up the wall, tucked under the siding or set behind counter flashing rather than smeared with sealant. Valley metal running the full length. A cricket behind a wide chimney. Fresh pipe boots. Drip edge at the eaves and rakes.
None of that is visible from the street once the job is finished, which is precisely why it gets skipped. It is also the difference between a roof that lasts its full service life and one that leaks in year four with the shingles still looking new.
If you are working out whether what you have is a repair or something bigger, how to tell if your roof has hail damage covers what storm damage actually looks like, and my own story and how I built Flagstone explains why I care about the parts nobody sees.
We do the parts you cannot see
I started Flagstone Roofing in 2011 with my wife, and we have completed roughly 3,000 roofs since. We are BBB accredited, GAF certified, TAMKO certified, an Angie’s List Super Service Award winner, and a member of the Roofing Contractors Association of Texas with licensing in progress. Every job carries a 7-year workmanship warranty and up to a 30-year manufacturer warranty.
We replace the flashing. We install the cricket. We put in new boots. Call 855-898-ROOF and ask us to show you the flashing line on the estimate — it should be there in writing.
Frequently Asked Questions
Should flashing be replaced with a new roof?
Yes in most cases. If a roof is being replaced because it is twenty years old, the flashing is also twenty years old and carries rust, old fastener holes and bends. New shingles over old flashing is a leak on a schedule.
What is step flashing?
Step flashing is individual pieces of metal installed one per shingle course where a roof meets a vertical wall, each lapped over the one below. A single continuous strip sealed with caulk is the faster substitute and it fails once the sealant ages.
What is a chimney cricket?
A cricket is a small peaked structure behind a chimney that splits water around it rather than letting it pool against the back wall. On wider chimneys it is frequently omitted because it takes time and skill, and that back edge then holds water.
Why do most roof leaks start at flashing?
Because water concentrates at joints. The middle of a shingle field sheds water easily; valleys, walls, chimneys and penetrations are where runoff collects and where any gap has something to exploit.
How do I know if flashing is in my roofing bid?
Ask directly which flashings are included: valleys, walls, chimney, pipe boots and drip edge. A bid that says re-roof and nothing more may include none of it, and you find out when it leaks.
How often do pipe boots need replacing?
The rubber collar around plumbing vents is among the first components to fail from sun exposure. Replacing boots during a re-roof costs very little, and leaving cracked older boots under new shingles is a predictable future leak.
