Built-Up Roofing (BUR)
A built-up roof is three or four plies of reinforced roofing felt bonded with hot asphalt and finished with gravel or a mineral cap sheet — the oldest flat-roof system still in service, and the most puncture-resistant. Grandview installs and replaces BUR on commercial buildings, shops, and flat-roofed homes across Utah County and Salt Lake County under a B100 general contractor license.
When a built-up roof beats the single-ply options
BUR earns its place on roofs that take abuse. Rooftop HVAC service, foot traffic, dropped tools, hail off the Wasatch — a gravel-surfaced built-up roof shrugs off what would puncture a 60-mil single-ply membrane. A cut through one ply still leaves two or three sealed plies underneath, and a repair is more plies mopped over the spot, not a membrane patch that has to be welded cleanly.
It’s also the right answer when you already have one. Many Utah commercial buildings from the 1960s through the 1990s carry an original gravel BUR, and if the deck and insulation are dry, re-covering in kind keeps the same proven detailing at the walls, curbs, and drains.
Where BUR loses: it’s heavy, it needs a hot-asphalt kettle on site, and it’s slower to install. For a lighter, reflective roof on a new addition, TPO roofing is the modern default. For BUR’s asphalt chemistry without the kettle, modified bitumen is its direct descendant — one or two factory-made sheets instead of four field-mopped plies. On a small residential flat roof where cost matters most, EPDM rubber is usually cheaper. The full range lives on our roofing page.
What goes into a built-up roof, ply by ply
- Tear-off and deck check. An old gravel BUR weighs four to six pounds per square foot, so removal is a real haul — chute, dumpster count, and deck inspection are planned together. Wet insulation gets cut out, never buried.
- Insulation and cover board. Polyiso insulation, tapered where the deck is dead flat, then a gypsum or high-density cover board so the hot asphalt bonds to a stable, fire-rated surface.
- Base sheet. A fiberglass base sheet, mechanically fastened or adhered. On a re-cover, this is where the new roof separates from the old one.
- Ply sheets in hot asphalt. Three or four Type IV fiberglass ply sheets, each mopped into asphalt heated to roughly 400–450°F and shingled so no two seams line up. Asphalt grade follows slope — Type III on near-flat decks, Type IV where the roof pitches enough that softer asphalt would slump in July.
- Flashings and edges. Cant strips at every wall and curb so the plies turn a 45° corner instead of 90°, modified bitumen base flashing up the walls, and a metal gravel stop at the perimeter. This is where built-up roofs fail when they fail.
- Surfacing. A flood coat of asphalt with roughly 400 pounds of embedded gravel per 100 square feet, or a mineral-surfaced cap sheet where weight or rooftop access rules out loose aggregate.
How Utah weather treats a built-up roof
The gravel does more than look traditional. At 4,500-plus feet, Utah’s UV oxidizes exposed asphalt in a few seasons; the aggregate shades the flood coat and is the main reason a well-drained BUR here reaches 20 to 30 years instead of 12. Where a reflective surface is wanted, a white mineral cap sheet or an aluminum coating gives the same protection with lower summer heat gain — the Department of Energy’s cool roof guidance is a fair summary of the trade-off.
Drainage decides the rest. A summer monsoon cloudburst can drop an inch of rain on a flat roof in under an hour, and water that stands past 48 hours is where plies blister. We size scuppers and drains for that storm and set tapered insulation to at least a quarter inch per foot, because October ponding becomes November ice, and the freeze–thaw cycling that follows pries gravel loose and works moisture into any ply edge it can find.
Weight matters on bench lots. Gravel BUR plus design snow load adds up, and a Draper or Alpine building carries a heavier winter than one in Provo. When the structure is marginal, a cap-sheet BUR or a PVC membrane takes a few pounds per square foot off the deck.
What does a built-up roof cost in Utah?
As a ballpark planning number, a new three- or four-ply gravel BUR in Utah County or Salt Lake County typically runs about $6.50 to $11.00 per square foot installed, including tapered insulation and flashings. A re-cover over a sound existing BUR lands at the low end; tearing off a wet, multi-layer gravel roof lands past the high end on hauling weight alone. Planning figures, not a quote — a written estimate follows a core cut and a walk of the roof.
- Ply count and surfacing. Four plies cost more than three; gravel flood coat costs less than a granulated cap sheet but adds weight and disposal cost next time.
- What’s under the old roof. Wet polyiso and rotted wood fiberboard get replaced at a unit price agreed before tear-off. A core cut tells us most of this up front.
- Penetrations and curbs. Every HVAC curb, vent, and pipe is a hand-flashed detail; a clean warehouse roof prices very differently from a restaurant roof with thirty of them.
- Access. Crane or conveyor for gravel and tear-off debris on anything above two stories.
If the existing roof is tired but dry, a restoration coating can buy five to ten years for a fraction of replacement — we’ll say so when that’s the honest answer.
Questions we actually get
Can you put a new built-up roof over my existing one?
Often, yes. If a core cut shows dry insulation, a sound deck, and only one roof already there, a re-cover with a new base sheet and plies is legitimate and cheaper than tear-off. Current Utah-adopted code limits total roof layers, and wet insulation anywhere in the field ends the re-cover conversation.
How long does a built-up roof last in Utah?
Plan on 20 to 30 years for a gravel-surfaced, properly drained four-ply BUR along the Wasatch Front. Ponding water and bare, UV-exposed asphalt shorten that; a coating applied around year fifteen commonly extends it. Three-ply and cap-sheet versions trend toward the lower end.
Is the hot-asphalt smell a problem for tenants?
It can be, so we plan for it: rooftop air intakes shut down or blocked during mopping, the kettle positioned downwind, tenants told the schedule in advance. For buildings that can’t tolerate any fumes or open flame, a cold-applied adhesive BUR removes the kettle entirely at a modest cost premium.
Who actually installs the roof?
Licensed roofing crews working under Grandview’s contract and supervision. We write the spec, set the ply and flashing standard, check the drainage layout before the first ply goes down, and walk the finished roof before sign-off. You hold one company accountable, and you can verify our B100 license at Utah DOPL.
Tell us what your flat roof is doing
We reply within a couple of hours during business hours — a day at most. You’ll get a straight read on re-cover versus tear-off, drainage, and budget before anyone commits. Built-up roofing is one of our site, structure and envelope services.