Walk across a gravel-surfaced flat roof in late winter and the footing tells the story: gravel pushed aside in a wide bald patch near the drain, a surface that crunches over a hump where a blister has risen, and a thin crack running along the edge of a roof section where the felts have split. A built-up roof is made of many layers, and a problem on the surface rarely stays on the surface.
Built-up roofing, usually shortened to BUR, is a system of alternating layers of asphalt and reinforcing fabric, finished with gravel or a mineral-surfaced cap sheet. In West Jordan, UT, where flat roofs carry snow and see wide temperature swings, BUR has a long record of surviving cycles that wear out thinner sheets. We build it, repair it and judge when the layers have had enough.
How the layers work together
A BUR is laid up in plies. A base sheet or insulation goes down first, then felts or ply sheets are set in hot asphalt or cold adhesive, one after another, each bonded to the one below. The finished roof has several layers of waterproofing in a continuous sandwich, and no single seam runs through the whole thickness. If a flaw opens in the top ply, the layers below still resist water.
That redundancy is the system's strength, and it also explains why damage tends to be hidden. Water that gets into a flaw spreads sideways between plies and may travel far before it appears as a stain. A roof walk, an infrared scan and a few core samples show where the layers are wet, and that map is more useful than the visible damage alone.
Hot asphalt, kettles and the work on site
A traditional BUR is installed with hot asphalt from a kettle on the ground or a tanker on the street, carried to the roof in a pipe or a bucket line. The work produces fumes and odor, and it calls for fire protection, protected edges and attention to wind direction, which carries smoke and smell toward neighboring tenants and air intakes. Cold-applied adhesives reduce the odor and heat, though they have temperature limits of their own.
On an occupied building, we plan the kettle location, the hoist and the hours to keep disruption small. Intakes near the work are covered or shut off with the mechanical contractor's help, and tenants are given a schedule for the strongest-smelling days. Because adhesives and asphalt both set poorly in cold, the Salt Lake Valley's winter freezing, recorded in the weather normals for Salt Lake City International Airport, pushes major BUR work into the warmer months.
Gravel, cap sheet or coating on top
The top of a BUR protects the asphalt from sunlight and gives the roof its traffic tolerance. Gravel is the classic surface: a layer of stone embedded in a flood coat of asphalt that shields the plies from UV and hail. It has weight and a rough texture, and it hides the roof, which makes leaks harder to trace. A mineral-surfaced cap sheet gives a cleaner, lighter surface that is easier to inspect. A reflective acrylic coating over the cap lowers surface temperature in summer, provided the cap is clean and firmly bonded.
Each choice carries a trade-off. Gravel blows or washes toward edges and drains, and it needs to be raked back and checked after storms and melt. A cap sheet wears with traffic and loses granules. A coating needs a clean, dry base and a periodic recoat. When we plan a replacement, we compare the three against the building's use and the weight the structure can carry.
Alligatoring, blisters, splits and ridges
As the asphalt at the surface oxidizes, it checks into a pattern of small cracks that resembles reptile skin, called alligatoring. Blisters form where air or moisture trapped between plies expands in sun. Splits open where thermal movement pulls the roof apart along a line, often above a deck joint or at a change in direction. Ridges rise along the felts where moisture has gotten between layers.
Each defect has a different level of urgency. A blister that has not broken is a warning, and one that has cracked is an open door to water. A split needs repair soon, since the winter freeze will widen it, and water that enters a split in January may not show on the ceiling until the thaw in March. We cut out damaged areas, dry the insulation if needed, replace plies and flood coat the repair, and where the roof is worn broadly we compare patching to a coating restoration for the whole surface.
Repair, restore or tear off
An aging BUR gives an owner three paths. The first is repair, which keeps the roof going with patches and flood coats. The second is restoration, with a coating or a cap added to the existing roof. The third is a full tear-off and new system. The wet insulation question governs which one is open, because a restored roof over wet boards just seals the moisture in.
We measure first: moisture by scan and core, thickness of the existing layers, slope to the drains and deck condition. A roof that is mostly dry with local damage suits repair, and one with scattered wet areas may be recovered after those areas are removed. When most of the insulation is wet, tear-off is the sound answer. A recover over a dry BUR is possible only if the structure carries the weight and the building code allows another layer.
Heavy industrial and warehouse roofs
Salt Lake City describes its Northwest Quadrant as holding most of the city's industrial and manufacturing sectors, with western warehouse and distribution facilities, and South Salt Lake names manufacturing, warehouse and distribution businesses among its local sectors. West Jordan reports access to I-15 and I-80, and its plan supports regional commercial and service development. Industrial and warehouse buildings often have large, low-slope roofs where a multi-ply system is a candidate, though a building's use does not tell us its roof type, so each one starts with a roof walk.
For owners in South Salt Lake, Salt Lake City or West Jordan, we assess the existing layers, the drainage and the structure before recommending BUR, modified bitumen or a single-ply. The match between roof and building use matters more than the system's name, and a drain that clogs with gravel will do more harm than any choice of membrane.
Commercial Roofing Questions
How long do the layers of a BUR hold up?
It varies with the number of plies, the surface, the exposure and the upkeep. A roof walk, moisture scan and core samples tell us more about a particular roof than any rule of thumb.
Why is gravel left on the roof?
It shields the asphalt from sunlight and hail and adds weight. It also needs to be checked after storms, because gravel that has shifted leaves bare spots where the asphalt wears.
Can a built-up roof be recovered?
Sometimes. The old roof must be dry, the deck sound and the structure able to carry another layer. A scan and core samples decide, and wet sections come out first.
What odors should tenants expect?
Hot asphalt gives off a strong smell. We position the kettle downwind of intakes, cover them where needed, and give tenants a schedule for the heaviest days.
What is a flood coat?
A heavy layer of asphalt poured over the top ply, usually with gravel embedded in it. It seals the surface and holds the stone in place.
Ask for a layer-by-layer look
Share the roof age, the surface type and where water or blisters have appeared. We will schedule a roof walk, core the roof where needed and confirm the repair boundary before work is priced.