A Roof With No Pitch Is A Different Trade

Where The Water Goes When There Is Barely Any Slope

On a shingle roof, water lands and leaves. That is why a shingle roof can be assembled from thousands of overlapping pieces and still keep a house dry: nothing has to be watertight, because gravity does the sealing.

A low-slope roof gets a quarter inch of fall per foot if it is lucky, and plenty of older buildings around town have less. Water does not leave, it wanders toward whatever is lowest, which after fifty years of settling is rarely where the original drain sits. So the roof has to be a genuinely sealed membrane, one continuous waterproof plane with every joint welded or bonded shut.

That flips every rule. On a membrane, every fastener, seam, drain bowl and pipe collar is a deliberate hole somebody made and then had to seal back up. The repair is not about replacing a damaged piece. It is about finding which seal quit.

Ponding Is Both The Symptom And The Cause

Water still standing forty-eight hours after the rain stopped is telling you two things at once, and people usually only hear the first one. As a symptom, it says the roof lost its geometry: decking sagged between joists, insulation compressed under years of foot traffic to the rooftop units, or a drain flush in 1985 now sits proud of the field because everything around it settled.

As a cause, it goes to work. Standing water magnifies ultraviolet exposure on the membrane under it, so that patch ages faster than the dry field ten feet away. It adds weight to the spot that already sagged, which deepens the sag, which collects more water. So when we find a pond we do not just patch under it. We look at whether the fix is tapered insulation, a drain reset, or a sump so the last inch actually leaves.

Membrane Types And The Specific Way Each One Quits

Arlington Heights has all of them. The mixed-use buildings near the station are mostly single-ply. The older brick storefronts still carry the built-up and modified bitumen roofs they have always had. The flat work behind houses is whatever was cheapest that year.

• TPO and other single-ply sheets are hot-air welded at the laps. A good weld is stronger than the sheet. A cold weld, made when the machine ran too fast or the sheet was dirty, holds for years and then peels along the lap.
• EPDM is the black rubber. The sheet is durable and failures are almost never in the field. They are at the seam tape, a different material with a different lifespan, and at the details where the rubber has to turn a corner and stay turned.
• Modified bitumen and built-up roofs fail by drying out. The asphalt loses its oils, the surface goes chalky, laps get brittle and open. On these we look for alligatoring first.
• Punctures cut across every system, and they are the hardest failures to find because the hole is often the size of a pencil.

Parapets And Curbs: Where Low-Slope Roofs Actually Die

The field membrane is rarely the problem. The problem is every place the flat plane has to stop being flat and go vertical.

Parapet walls are the classic one downtown. The membrane runs up the inside face and terminates, and that termination has to be sealed and mechanically held. Above it sits masonry with mortar joints and a coping on top. Mortar joints soften. Coping stones crack or the joints between them open. Water enters at the top of a wall nobody looks at, runs down inside the cavity, and appears as a ceiling stain along the exterior wall. Everybody blames the roof field, and the field is fine.

Curbs are the other one. Every rooftop unit, hatch and skylight sits on a raised box with four inside corners where the membrane gets cut, folded and detailed by hand. We check curbs early, because a mechanical contractor swapping a condenser will happily set the new unit on flashing he never touched.

What A Chicago Winter Does To Every Seam Up There

This is where the problem gets genuinely local. A low-slope roof holds water, and northwest Cook spends months crossing back and forth over freezing, sometimes twice in a day when a February afternoon gets sun. Every crossing is a cycle, and it happens exactly where you cannot afford it: in the pond, in the seam running through the pond, in the drain that iced shut and turned the whole field into a pond.

Water expands when it freezes. Under a lifted lap or inside a hairline crack in aging modified bitumen, that expansion is a wedge driving the opening wider every cycle. A seam weeping a teaspoon in November is open in March. That is the pattern we see every spring: roofs fine in the fall and leaking by the thaw.

It also changes when we can do what. Adhesives need temperature to bond, so a January leak often means a solid temporary patch now and the permanent detail on the first workable stretch. Wind and hail season runs through storm damage repair here in town.

Doing Roofs Is Not The Same As Doing This One

Plenty of good shingle crews are genuinely good at shingles. Low-slope is a separate skill set with separate tools: a hot-air welder and the judgment to run it at the right speed, torch experience on modified bitumen, and enough hours on membrane to know a cold weld by feel. A crew without those caulks the spot above your stain, which is usually not the leak.

Flat systems have been part of what this shop does since Angelo took it over from his father Frank, alongside the shingle work across the ranch and split belts here. If the field is past patching, that job is on the flat roof replacement page. Low-slope work is in the gallery, or send photos through the contact page.