Commercial Masonry · Chicagoland, IL

Is Your Commercial Building's Leak Coming From the Roof or the Masonry? How to Find the Real Source

A roofer says the roof is fine. The ceiling is still wet. On commercial buildings in Chicagoland, a large share of leaks blamed on the roof actually start in the parapet, the coping, the mortar joints or a window sealant joint. Here's how to work out where the water is really coming from before you pay to fix the wrong thing.

2026-11-05

Quick Answer

To tell whether a commercial building leak comes from the roof or the masonry, note when it leaks, where it appears and what's above it. Leaks during wind-driven rain, along exterior walls or below parapets often start in coping, joints or sealant. Paul Lally's Masonry, family-owned and insured since 1988, traces them across Chicagoland: (708) 448-8866.

Is Your Commercial Building's Leak Coming From the Roof or the Masonry?

To tell whether a commercial building leak comes from the roof or the masonry, look at three things: when it leaks, where the water shows up and what's directly above it. A leak that follows wind-driven rain from one direction, runs along an exterior wall or sits right under a parapet usually starts in the masonry or sealant. A leak in the middle of the floor plan, in any steady rain, usually starts in the roof or a drain.

Paul Lally's Masonry, a family-owned, insured masonry contractor serving Chicagoland since 1988, traces and repairs these leaks for property managers, condo boards, churches, schools and building owners. Call (708) 448-8866 for a free on-site estimate.

It's a familiar story. There's a stain on the top-floor ceiling. The roofer patches the membrane. It rains, and the stain comes back. The roofer returns and says the roof is fine. Everybody's right, and the building is still leaking, because the water is coming in above the roof.

Water doesn't care which contractor's scope it's in. On a commercial building, the top of the wall and the edge of the roof are one system, and leaks love the place where two trades meet.

How water actually moves through a masonry wall

Masonry isn't waterproof, and it was never meant to be. Brick and mortar absorb water like a stiff sponge. A healthy wall deals with that by shedding most of it, storing some in the masonry until it dries out, and draining the rest with through-wall flashing and weep holes.

Leaks start when one of those functions fails. Three facts explain most confusing leaks:

Water travels. It enters high up and runs down inside the wall, along steel or across the top of the flashing, then comes out somewhere else.
Wind pushes it in. Wind-driven rain gets through gaps that ordinary rain never would, which is why some leaks only show up in certain storms.
Freeze-thaw widens the path. Chicagoland's winters take a hairline crack and open it a little further every year.

When and where: reading your leak

Before anybody climbs a ladder, write down what the leak does. This table narrows things down faster than almost anything else.

What the leak does	Most likely source
Only in wind-driven rain from one direction	Wall, window sealant or parapet on that side
In any steady rain, middle of the floor plan	Roof membrane, drain or penetration
Along the top of an exterior wall	Parapet, coping, counterflashing
Over a window or door, along the head	Lintel flashing, wall above, or window sealant
Low on the inside of a block wall	Water inside the cores, entering higher up
At snowmelt or after a thaw	Ice at the parapet base, flashing, roof edge
Hours or a day after rain stops	Water stored in the wall draining slowly
On dry days	Plumbing, HVAC condensate or condensation, not masonry

The masonry sources roofers often get blamed for

Coping

Coping is the roof over your wall. When its joints open, or the sealant between pieces fails, water drops straight into the parapet. Metal coping can leak at its laps, seams and fasteners. Without flashing under it, there's nothing to stop that water from entering the building.

Parapet walls

A parapet takes weather on both faces and the top. Failed mortar joints on the back of the parapet are hard to spot from the ground, and they sit right above the roof flashing. Water gets in there and runs down behind the roofing, which is why a good roof can appear to leak.

Counterflashing

Counterflashing covers the top of the roof's base flashing and is set into the masonry. When the joint it's set in fails or the metal pulls out, water runs behind the roofing. This one sits squarely between the two trades, and it's often missed for that reason.

Rooftop masonry

Stair towers, elevator penthouses, chimneys and fire walls all take weather on every side. A leak near any of them should get them inspected first. See our guide to rooftop masonry on commercial buildings.

Mortar joints and cracks

Worn or receding mortar joints, stair-step cracks and vertical cracks at corners let water in on the wall itself. Weather-facing elevations go first.

Sealant joints

Failed sealant around windows, at control joints and between trim pieces is one of the most common leak sources on commercial buildings, and it's easy to confuse with a window leak.

Lintels and missing flashing

Steel over windows and storefronts should have through-wall flashing with end dams above it and weep holes to let the water out. Without it, or when it fails, water shows up at the window head. Rust there is a warning sign.

Blocked weep holes

Weep holes filled with mortar, mulch or old sealant trap water inside the wall until it finds another way out, usually into the building.

Warning signs that point to the wall, not the roof

Efflorescence (white salt deposits) on the outside or inside of the wall.
Peeling paint or plaster on the inside face of exterior walls.
Dark damp patches on the outside that stay long after rain.
Spalling brick on parapets or below coping.
Rust staining at lintels and shelf angles.
Stains that line up with the wall rather than the roof deck.

How a professional traces a leak

Get the history: when it started, which storms, what's already been repaired, and photos of the stain over time.
Map it inside, marking every stain and damp area on a simple plan of the building.
Inspect directly above and upward: the wall, the windows, the parapet, the coping and the rooftop masonry.
Inspect with the roofer when possible, since the roof edge belongs to both trades.
Water test if needed: wet one small area at a time, low to high, at low pressure, with someone watching inside.
Open a small area if it's still unclear, to check flashing or look inside the wall.
Write it up: the source, the fix and what can wait, sorted by risk and by elevation.

Materials and techniques for a lasting repair

Repointing with Type N or Type S mortar matched to the wall, with joints ground out to a sufficient depth for the new mortar to bond properly.
Coping reset or replacement, sloped toward the roof, with flashing beneath it.
Through-wall flashing with end dams and weep vents at lintels and parapet bases.
Commercial sealant with backer rod, with the old sealant fully removed.
Breathable silane or siloxane repellents where they make sense, after repairs. Never a film-forming coating on a wet wall.

What drives the cost of a masonry leak repair

We don't publish prices, because leaks aren't scoped alike. What drives the cost:

Where the water enters: a sealant joint is a very different job from a parapet rebuild.
Height and access: lifts, scaffolding and roof protection.
How long it's been leaking: rusted steel, corroded ties and wet insulation add scope.
Coordination with the roofer and interior trades.
Phasing around tenants and operations.

The tracing itself saves money, because the most expensive repair is the one that fixes the wrong thing. Call (708) 448-8866 for a free on-site estimate.

What to do the day a leak appears

You don't need to know the source yet to do the useful things:

Protect people and contents first. Move equipment and records, and put out buckets. If a ceiling is sagging or wet near lights, keep people clear and call an electrician.
Photograph everything: the stain, the date, the weather, and the same spot again next time.
Note the wind direction. Weather records make this easy to check later, and it's often the most useful clue you'll have.
Check the simple things on the roof if it's safe: blocked drains, ponding water, debris against a parapet.
Don't caulk anything yet. Sealing the wrong spot can move the leak somewhere else and hide the evidence.

Roof warranties and masonry leaks

Before a leak gets argued over, read the roof warranty. Many warranties cover the roofing system, not water that enters through the walls, coping or flashing that belongs to the wall. They may also have rules about who can touch the roof, so don't let anyone cut into the membrane or base flashing without checking first.

That's another reason to get the roofer and the mason on the roof together. When both are looking at the same parapet base, the question of whose problem it is usually gets answered in minutes. It also gets the repair sequenced properly, with masonry and through-wall flashing done before the roofing is tied back in.

DIY vs. hiring a pro

Building staff can do valuable work here: keep a leak log, take photos, clear roof drains and clear weeps. But caulking over mortar joints, smearing roof cement on masonry or painting a wet wall tends to hide the leak, trap water and make the eventual repair bigger. Work at parapets also brings real fall risk, so it needs proper equipment and insurance.

Why Chicagoland buildings leak this way

Lake-driven storms, dozens of freeze-thaw cycles a year and wide temperature swings work on the same details again and again. Older solid brick buildings in Chicago, in Oak Lawn and along the older commercial streets have parapets and steel lintels that have outlived their flashing. Newer veneer buildings in DuPage and Will counties reach their first round of sealant and flashing problems around their second decade. Block buildings across the region's industrial parks take water into their hollow cores.

Building type	Leak sources to check first
Condo and apartment buildings	Parapets, chimneys, rear-wall lintels, balcony connections
Churches	Towers, stone trim, large window openings, valleys against walls
Schools	Block control joints, gym parapets, long roof edges
Strip retail	Front parapet, storefront lintel, sign penetrations
Office and medical	Window sealant, shelf angles, precast joints
Warehouse and industrial	Block parapets under metal coping, overhead-door heads

Preventing the next leak

Walk the roof and parapets every year, ideally in spring.
Check sealant on every elevation, and replace it before it opens up.
Keep drains and weeps clear.
Bring both trades together when the roof is replaced, so flashing and masonry are coordinated.
Keep a leak log, because a record of what leaked and when is worth a lot.

For a full plan, see our commercial masonry maintenance schedule, and read more about how water gets through a brick wall.

Related services

Find the source before you pay for the fix

Paul Lally's Masonry Inc. is a family-owned, insured masonry contractor serving Chicago and the Chicagoland suburbs since 1988 — tuckpointing, brick repair and replacement, chimney repair and rebuilds, lintel replacement, masonry restoration and waterproofing for commercial and residential properties. Built on Craftsmanship. Backed by Experience. Free on-site estimates — call (708) 448-8866.

If the roof has been patched and the leak keeps coming back, have the wall looked at. We'll trace the water, show you where it's getting in, and give you a written plan. We're insured, we provide a certificate of insurance before work starts, and we stand behind our work, because our name is on every job.

Request a free on-site estimate or call (708) 448-8866.

Frequently Asked Questions

How can I tell if a leak is from the roof or the masonry?

Look at when and where it leaks. A leak that follows wind-driven rain from one direction, runs along an exterior wall or sits right below a parapet often points to the masonry. A leak in the middle of the floor plan, away from any wall, more often points to the roof, a drain or plumbing.

My roofer says the roof is fine, but the ceiling still leaks. Who do I call?

Call a masonry contractor to look at the parapet, coping, wall joints, flashing and window sealant. Water often enters the wall above the roof line and runs down behind the roof flashing, so it looks like a roof leak but isn't one. Paul Lally's Masonry can inspect it at (708) 448-8866.

Can water really get through a brick wall?

Yes. Brick and mortar absorb water, and heavy wind-driven rain gets through hairline gaps and worn joints. A healthy wall handles this with flashing and weep holes that send the water back out, so leaks usually mean that system has failed somewhere.

Why does our concrete block building leak low on the wall?

Hollow block has open cores. Water that gets in high up, at a parapet, joint or crack, runs down inside and comes out near the floor, often far below where it entered. That's why the visible wet spot rarely marks the actual source.

Why does our building leak only in certain storms?

A leak that only shows up when rain comes from one direction usually means the water's getting in through a wall, window or parapet on that side. A leak in any steady rain points more toward the roof or drains, and one that appears on dry days points toward plumbing or condensation.

Does a water test damage the building?

No, not when it's done properly. A controlled test wets one small area at a time at low pressure, starting low and working upward, so you can see which area starts the leak.

Will sealing the wall stop the leak?

Rarely on its own. A repellent can reduce water absorbed through the face of the brick, but it won't fix failed coping, flashing, open joints or sealant, and a film-forming coating can trap water. Repair the entry points first.

How much does it cost to fix a masonry leak on a commercial building?

It depends on where the water's getting in, the building's height and access, how much coping, flashing or repointing is involved, and any damage inside the wall. We don't publish prices; we give an itemized written scope after a free on-site estimate.

Who diagnoses commercial building leaks in Chicagoland?

Paul Lally's Masonry, a family-owned, insured masonry contractor serving Chicago and the suburbs since 1988, traces and repairs masonry leaks on commercial, association, church and school buildings. Call (708) 448-8866 for a free on-site estimate.

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