BEMS research

Commercial Roof Systems We Manage

The roof systems Inspec manages through BEMS for Chicago and Milwaukee owners: EPDM, built-up, modified bitumen, metal, PVC and TPO, by area and age.

15.3 millionsquare feet of roofing in the systems below

3,241roof sections

11roof system types

Inspec manages roof portfolios for building owners through BEMS, our building envelope management system. This page summarizes the roofs held in BEMS for clients of our Chicago and Milwaukee offices: what they are, how much of each there is, and how old they are today. Every figure is an aggregate across many buildings; no individual building or owner can be identified.

By area

Roof systems in the portfolios we manage

Roof system types, largest first
Roof system	Roof sections	Square feet	Median age	Oldest 10% are at least
EPDM, fully adhered	820	4,326,738	17 years	29 years
Built-up roof (BUR), aggregate surfaced	772	4,192,294	22 years	37 years
Modified bitumen, granule surfaced	391	1,833,373	14 years	26 years
EPDM, ballasted	296	1,523,408	25 years	35 years
Built-up roof, coal-tar pitch	109	835,785	22 years	49 years
Standing-seam metal, prefinished	312	739,427	16 years	28 years
PVC, fully adhered	221	618,154	13 years	24 years
Asphalt shingles	139	553,854	24 years	30 years
TPO, fully adhered	110	488,430	12 years	20 years
Structural metal panel	37	178,610	28 years	40 years
Standing-seam metal, copper	34	44,586	36 years	63 years

Roof systems explained

What each roof system is, and why owners choose it

A plain-language guide to the systems above. The right choice for a building depends on its structure, slope, use and budget — which is what a roof consultant weighs before a replacement is designed.

EPDM, fully adhered

A single-ply synthetic rubber membrane (ethylene propylene diene monomer) bonded to the insulation or roof deck with adhesive across its whole surface.

Why it is used: EPDM stays flexible through hot summers and cold winters, has a long track record on low-slope commercial roofs, and adhering it fully resists wind uplift without adding the weight of ballast. It adapts well to roofs with many penetrations and irregular shapes.
What to watch for: Seams and laps, where sheets are joined with tape or adhesive, are the most common source of leaks, along with flashings at walls, curbs and penetrations.

In the portfolios we manage: 820 roof sections, 4,326,738 sq ft, median age 17 years.

Built-up roof (BUR), aggregate surfaced

Several plies of reinforcing felt laminated together with hot asphalt, finished with a flood coat of asphalt and a layer of embedded gravel.

Why it is used: Multiple plies give redundancy — one damaged layer does not mean a leak — and the system has been used on commercial roofs for well over a century. The gravel protects the bitumen from sunlight, weather and foot traffic.
What to watch for: Blisters between plies, bare spots where gravel has shifted, and flashings at walls and penetrations. The gravel surface also makes the membrane harder to inspect and leaks harder to locate.

In the portfolios we manage: 772 roof sections, 4,192,294 sq ft, median age 22 years.

Modified bitumen, granule surfaced

Factory-made rolls of asphalt modified with polymers (SBS or APP) around a reinforcing mat, usually installed in two or more plies with a cap sheet surfaced in mineral granules.

Why it is used: It combines the multi-ply redundancy of a built-up roof with the consistency of factory-made sheets. It is tough under foot traffic and punctures, can be installed several ways — torch-applied, hot-mopped, cold adhesive or self-adhered — and the granules protect it from sunlight.
What to watch for: Laps and seams depend on installation quality, granules wear away with age and expose the bitumen, and flashings at walls and curbs are frequent leak points.

In the portfolios we manage: 391 roof sections, 1,833,373 sq ft, median age 14 years.

EPDM, ballasted

The same rubber membrane laid loose over the insulation and held in place by the weight of river rock or concrete pavers rather than adhesive or fasteners.

Why it is used: Ballasted roofs install quickly with few attachments, the stone shields the membrane from sunlight and foot traffic, and the membrane is simple to lift and inspect or reuse.
What to watch for: The structure must be able to carry the ballast, stone can be scoured away at corners and edges in high winds, and the ballast hides the membrane — which makes leaks harder to trace.

In the portfolios we manage: 296 roof sections, 1,523,408 sq ft, median age 25 years.

Built-up roof, coal-tar pitch

A built-up roof that uses coal-tar pitch instead of asphalt as the bitumen between plies, surfaced with gravel.

Why it is used: Coal-tar pitch softens and flows in warm weather, which lets small cracks close up on their own. It is suited to dead-level roofs where water ponds, and older coal-tar roofs are often still in service after many decades.
What to watch for: It is only suitable on roofs that are flat or very nearly so, repairs call for compatible materials and experienced crews, and installation involves fumes that require health precautions.

In the portfolios we manage: 109 roof sections, 835,785 sq ft, median age 22 years.

Standing-seam metal, prefinished

Steel or aluminum panels with a factory-applied finish, joined by raised interlocking seams and held down by concealed clips rather than exposed fasteners.

Why it is used: Standing seams sit above the water line and shed rain and snow well, the clips let panels expand and contract with temperature, and the finished metal needs little routine maintenance.
What to watch for: Leaks usually start at penetrations, trim and flashings where the roof meets walls or changes plane, and at seams that have been damaged or poorly formed. The roof needs enough slope for the panel profile.

In the portfolios we manage: 312 roof sections, 739,427 sq ft, median age 16 years.

PVC, fully adhered

A thermoplastic single-ply membrane (polyvinyl chloride) whose seams are heat-welded into one continuous sheet, bonded to the substrate with adhesive.

Why it is used: Welded seams are often stronger than the membrane itself, PVC resists grease and many chemicals — useful near restaurant exhausts and some industrial processes — and it is usually light-colored and reflective, which reduces heat gain.
What to watch for: Seam welds depend on workmanship, the membrane can become less flexible as it ages, and PVC must be kept separated from asphalt and some other materials it is not compatible with.

In the portfolios we manage: 221 roof sections, 618,154 sq ft, median age 13 years.

Asphalt shingles

Overlapping asphalt shingles over an underlayment on a sloped roof, shedding water by gravity.

Why it is used: They are familiar, economical, and easy to repair in small areas. On commercial and institutional campuses they often cover steep-sloped buildings such as schools, churches, housing, mansards and dormers.
What to watch for: Shingles need enough slope to shed water, and problems tend to start with wind-lifted or missing shingles, ice damming at the eaves, and flashing at valleys, walls and penetrations.

In the portfolios we manage: 139 roof sections, 553,854 sq ft, median age 24 years.

TPO, fully adhered

A thermoplastic single-ply membrane (thermoplastic polyolefin) with heat-welded seams, typically white, bonded to the substrate with adhesive.

Why it is used: Its reflective white surface reduces cooling loads, welded seams form a continuous membrane, and it is one of the most widely installed systems on new commercial roofs because it combines those qualities with a competitive installed cost.
What to watch for: Seam welds and flashing details depend on installation quality, formulations differ between manufacturers, and the surface can be damaged by heavy foot traffic and dropped tools.

In the portfolios we manage: 110 roof sections, 488,430 sq ft, median age 12 years.

Structural metal panel

Metal roof panels strong enough to span between the building's structural supports on their own, without a solid deck beneath them.

Why it is used: Common on industrial and pre-engineered metal buildings, where they cover large, simple roofs economically and install quickly.
What to watch for: On exposed-fastener panels the rubber washers under the screws age and loosen with thermal movement; panel laps, end laps and penetrations are the usual leak points.

In the portfolios we manage: 37 roof sections, 178,610 sq ft, median age 28 years.

Standing-seam metal, copper

Standing-seam panels formed from copper, which weathers naturally to a brown and then green patina.

Why it is used: Copper is chosen for longevity and appearance — on historic and institutional buildings, towers, domes, bays and accent roofs where the roof is part of the architecture.
What to watch for: It is costly and needs skilled craftspeople; soldered joints and flashings are the usual points of failure, and runoff can stain materials below.

In the portfolios we manage: 34 roof sections, 44,586 sq ft, median age 36 years.

How these figures were produced

Totals come from roof sections recorded in BEMS for clients of Inspec's Chicago and Milwaukee offices, as of September 2026. Ages are measured from each roof's recorded install date. Roof types held by too few owners to report without identifying them are left out.

Managing a portfolio like this? See how BEMS works, or talk to an Inspec roof consultant.

Common questions

How long does a commercial roof last?

It depends on the roof system and on how it was designed, installed and maintained, so no single number is honest. What we can show is how old the roofs in service actually are. Across the 3,241 roof sections Inspec manages through BEMS for Chicago and Milwaukee owners, the median age runs from 12 years for TPO to 36 years for copper standing seam, and in nine of the eleven systems the oldest 10% are at least 26 years old.

These are ages of roofs still in service, not warranty periods or predictions. Whether a particular roof has years left is what a roof condition assessment answers.

How long does an EPDM roof last?

In the portfolios we manage, the 820 fully adhered EPDM roof sections have a median age of 17 years, and the oldest 10% are at least 29 years old. The 296 ballasted EPDM sections are older: a median of 25 years, with the oldest 10% at least 35.

Seams and laps, along with flashings at walls, curbs and penetrations, are the most common sources of leaks on EPDM roofs.

How long does a built-up roof last?

The 772 gravel-surfaced built-up roof sections we manage have a median age of 22 years, and the oldest 10% are at least 37. Coal-tar pitch built-up roofs, 109 sections, have the same median of 22 years, but their oldest 10% are at least 49 years old, the oldest of any membrane roof in these portfolios.

TPO, PVC or EPDM: which lasts longest?

In our portfolios the fully adhered TPO roofs are the youngest (110 sections, median age 12 years, oldest 10% at least 20), then PVC (221 sections, median 13, oldest 10% at least 24) and fully adhered EPDM (820 sections, median 17, oldest 10% at least 29).

A younger median partly reflects when those roofs were installed, not only how long the material lasts, so the figures compare the roofs in service rather than each material's limit. The right choice for a building depends on its structure, slope, use and budget.

What is the most common commercial roof type?

In the portfolios Inspec manages for Chicago and Milwaukee owners, fully adhered EPDM covers the most area: 4.33 million square feet across 820 roof sections. Gravel-surfaced built-up roofing is close behind at 4.19 million square feet across 772 sections. Together they are more than half of the 15.3 million square feet in the systems we report.