When replacing a roof on a building with an addition, the junction where the two structures meet needs a careful flashing inspection before any new materials go down. Even if there are no active leaks, existing flashing at that transition point may need to be replaced or upgraded to perform correctly under a new roof system. Getting this step right protects the entire investment.
We recently spoke with a property manager in the Sidney, IL area who was updating a roof replacement estimate for a building with an older original structure and a newer addition attached to it. There was no active leak at the junction, but the trustees wanted to make sure a qualified crew would evaluate that transition point closely and address anything that needed attention.
It is a smart question and one we do not hear often enough. At White Roofing and Contracting, we run into this situation regularly on churches, community buildings, and commercial properties throughout central Illinois.
Why Is the Junction Between an Addition and an Original Structure a Risk Area?
Where two roof planes or two separate structures meet, water has more opportunities to find a path inside. The original building and the addition may have been built years apart, with different framing, different settling patterns, and different roofing materials. Over time, that transition point can shift slightly, causing flashing to pull away or develop gaps.
Common issues we find at these junctions include:
- Step flashing that has corroded or separated from the wall
- Counter flashing that was never properly embedded or sealed
- Caulk that was used as a substitute for proper metal flashing
- Gaps where two roof decks meet at different heights
- Missing kick-out flashing that should redirect water away from a wall
The fact that there is no current leak does not mean the existing flashing is in good shape. It just means it has not failed yet.
Should Existing Flashing Always Be Replaced During a Roof Replacement?
Not always, but it should always be inspected, and replacement is often the right call. When we tear off old roofing materials, we get a clear look at flashing condition that is not possible from the ground or even from a basic visual inspection on the roof. If the metal is solid, properly sized, and correctly installed, we can work with it. If there is any doubt, replacement is the smarter and more cost-effective choice in the long run.
For penetrations like plumbing vents and pipe boots, we never reuse rubber boots. They degrade over time, and installing a new roof over an old boot is a leak waiting to happen. Larger commercial penetrations like kitchen exhaust vents are different. We evaluate those case by case. If the existing flashing is properly sealed and structurally sound, it may not need to be replaced.
Our roof replacement process includes a full review of all penetrations and transition points before we finalize scope and pricing.
What Should Property Managers Ask Their Roofing Contractor About Addition Junctions?
Before work begins, ask your contractor directly whether the junction area is included in the scope and what their plan is if they find a problem. You want clear answers, not vague reassurances.
Good questions to ask include:
- Will you inspect the flashing at the addition-to-original-building transition before finalizing the estimate?
- Is replacement of that flashing included in the base price, or is it a potential add-on?
- What does proper flashing look like at this type of junction, and can you show me?
- What happens if you find rot or damaged decking under the flashing once tear-off starts?
A contractor who has done this kind of work before will have direct answers. Our experienced team walks property owners and managers through exactly this kind of evaluation before a single shingle comes off.
Frequently Asked Questions
Can we skip replacing the flashing if there are no current leaks?
You can, but it is a gamble. Old flashing that appears to be holding can fail quickly once new roofing materials change the load and movement dynamics. Addressing it during a planned roof replacement is far less expensive than dealing with water damage after the fact.
What is the difference between step flashing and counter flashing at a wall junction?
Step flashing is installed in layers between each course of shingles and the wall. Counter flashing is embedded into the wall above it and overlaps the step flashing to block water. Both need to be present and properly sized. Missing one or the other is a common source of leaks at addition junctions.
Does the slope of the roof affect how the junction flashing is handled?
Yes. A lower-slope roof moves water more slowly and holds it longer, which puts more stress on flashing details. At shallower pitches, flashing laps and sealant choices become even more critical. We adjust our approach based on the actual slope of each roof section.
If you manage a church, commercial property, or any building with an addition attached to an older structure, do not leave the flashing question to chance. Contact White Roofing and Contracting to schedule a roof evaluation in Sidney, IL and the surrounding area. We will take a close look at every transition point and give you a clear, honest assessment of what needs to be done.