A seam is a line, and a line is priced by the foot. That is the simplest way to compare seam repair bids, and it is the way we write ours. A single-ply roof is a set of sheets joined at hundreds of feet of seams, and a few feet of open seam can let in enough water to wet the insulation across a bay. A seam that opens in the thaw takes in meltwater all spring, and the city rates Coeur d'Alene weathering as severe.
We probe every seam we can reach, mark the ones that are open or weak, and price each run. The owner sees how many feet need work and what each foot costs.
The Call: Weld, Strip or Replace the Sheet
Three repairs cover most seam failures. Re-welding a thermoplastic seam works when the membrane is clean and still weldable. A cover strip, a band of new membrane welded or adhered over the seam, works when the edge is damaged or the old surface is too aged to weld. Replacing the sheet works when the seam failure is widespread in one area, or the membrane has shrunk and pulled the seam apart.
The membrane type changes the details. Thermoplastic sheets such as TPO and PVC are welded with hot air, and a weld fails when it was cold, dirty or too fast. EPDM seams are tape or adhesive and fail when the splice surface was contaminated or the primer was missed. Modified bitumen laps open when heat or adhesive was short. We identify the system first, because the repair follows from it. A building in Hayden with a light-industrial or aviation roof may carry a different membrane from a retail strip in Coeur d'Alene, and one roof can even have two systems from two different reroofs. Where the seam type is not obvious, a small cut sample tells us what we are dealing with, and the cut is patched the same day.
What It Costs: Linear Feet, Not Square Feet
A seam repair is priced per linear foot, with a minimum for mobilization. Probing and marking is the first line. Re-welding is the next. Cover strips add material and labor. Replacing a sheet is priced by area. Corners and T-joints, where three layers meet, cost more than straight seams, since they are the hardest to weld and the most likely to fail again.
The hidden line is wet insulation. A seam that has leaked for a season may have soaked the board under it, and the repair has to include moisture checking and any board replacement. We carry that as a unit-price allowance. If a roof shows seam failures across most of its length, a commercial roof repair list can still make sense, but a recover or replacement may be cheaper per year of life. We price both so the owner sees the choice.
What the Code Sheet Says: Wind and Freeze Test Every Seam
Wind flutters the membrane, and flutter fatigues welds and tapes over time. Freeze and thaw works water into the smallest gap, and ice widens it. A seam that is tight in September can show a hairline gap in March, and a gap that small is easy to miss from standing height, which is why the probe and a flashlight do the work.
The temperature swing is large. In Coeur d'Alene the January mean sits near 31 F and the July mean near 70 F, about 18 days a year pass 90 F, and the record low is minus 30 F, a swing that tugs at every lap. A membrane that moves with those swings pulls on every seam, and one that has shrunk with age pulls harder. We probe in the cool part of the day, when the membrane is tight and open seams show.
Snow adds its own test. Snow of about 59 inches a year at Post Falls is the regime behind commercial roof design on the Rathdrum Prairie. A seam that sits under a persistent drift stays wet for weeks, and meltwater finds any gap in it. After a heavy winter, the spring walk is the moment to find the seams the snow opened, before the summer heat and foot traffic enlarge them.
Where It Fails First: T-Joints, Laps Under Ponds and Edges
The weakest seams are T-joints, seams under ponds and seams near edges and penetrations. T-joints stack three layers and often leave a small void. Ponds soak seams and hasten aging. Edges and penetrations bring movement and foot traffic. Seams along the direction of prevailing wind, which flutter first, also show failure early.
We walk the roof along each seam line and press with a probe. An open seam lets the probe slide in. A weak seam peels with light pressure. A good seam resists. For a large flat roof at Riverbend Commerce Park, with many rooftop units, we check around each curb, since foot traffic stresses the seams there. A roof that ponds will have worse seams near the pond, and the ponding water repair scope handles the cause so the seam repair lasts.
Alternates: Test Welds, Coatings and Walk Pads
Choices include a cover strip over every T-joint on the roof, a test program with probe records, walk pads on routes that stress seams, a seam sealer on aged EPDM, or a coating over a roof that is sound apart from its seams. Each is its own line, and each depends on the condition of the membrane.
If seams keep opening, the question changes. A roof that has been repaired for several seasons, with seam failures in many places, is telling the owner the membrane is at the end of its life. We say so, and we price the replacement beside the repair. The comparison uses cost per year of added life, not the up-front price, because a cheap repair that buys one season costs more over five years than a firm plan. For roofs with sound sheets and tired seams, a repair and coating plan can add years. We take cores and a moisture scan before recommending it, since a coating over wet insulation fails.
Schedule and Snow Window: Weld Weather
Welding and bonding need dry membrane and moderate temperatures. Cold seams do not fuse well, wet seams do not bond and frost blocks the surface. In Coeur d'Alene the usable window runs from spring thaw through early fall. A seam that opens in January is sealed temporarily with a cold-applied cover and re-welded in spring.
We also keep a seam record, because a seam that was fixed once and failed again tells a different story from one that has never been touched. Each repair is logged by location and length with a photo, so the next visit can see whether a repaired seam is holding. The record goes into the preventive maintenance file. If the failure is tied to flashing at the same location, the flashing failure repair scope is done with it, so the area is not opened twice.
Commercial Roofing Questions
How do you find an open seam?
We probe along the seam line. An open seam takes the probe. We mark and photograph each one.
Can open seams be repaired in winter?
Temporarily. Permanent repair needs dry membrane and moderate temperatures.
What causes seams to open?
Contamination, cold or fast welding, thermal movement, ponding water and wind flutter.
Is a cover strip as good as a new weld?
It is a sound repair when the old edge is damaged or aged. It adds a second line of defense.
When is seam repair no longer enough?
When failures appear across most of the roof or the membrane has shrunk. Then a recover or replacement costs less per year.