Gravel BUR to TPO or Modified Bitumen: What Has to Come Off First
Every gravel built-up roof that reaches end of life has the same first step. The stone comes off before anything else can happen, and what it was hiding decides the rest of the job.
The short answer
A gravel-surfaced built-up roof cannot be recovered, coated or torn off until the gravel is vacuumed off. The stone is the first line of every replacement path, and once it is gone the condition of the exposed plies and the deck decides whether the roof is a tear-off and new TPO or modified bitumen, a recover over the old plies, or a coating. Nobody can honestly tell you which until the stone is off. The removal itself is described on our gravel roof vacuuming and ballast removal page; this guide is about what happens next.
What a gravel BUR actually is
Built-up roofing is three to five plies of reinforcing felt bedded in hot asphalt, finished with a flood coat of asphalt and pea gravel pressed into it. The gravel protects the asphalt from sunlight and foot traffic, which is why the system lasts as long as it does on Chicago industrial buildings. It also hides everything. Blisters, open laps, splits over joints, ponding and wet insulation are all invisible under the stone, and a leak that has been chased for years often turns out to be a lap that was open the whole time. Our comparison of modified bitumen against built-up roofing covers the two systems side by side.
Step one, always: the gravel comes off
On a whole roof the gravel is vacuumed: a trailer unit at grade, hose up the face, crew on the roof working the field in lanes. Embedded pea gravel comes off with some of the flood coat, which is expected, at roughly 10,000 to 15,000 square feet per crew-day. As the field clears, the crew documents what appears, because that read decides the rest of the project. A core cut or a moisture scan on the exposed plies tells you whether the insulation is dry. Wet insulation changes the answer from a recover to a tear-off, and it is far better to know that before the new material is ordered than after.
Path A: tear-off and new TPO or modified bitumen
If the plies are saturated, the insulation is wet, or the deck needs work, the old roof comes off down to the deck and a new system goes on: new insulation to current code, a cover board, and either a heat-welded TPO membrane or a two-ply modified bitumen system. This is the clean reset. It costs the most, it resets the warranty clock fully, and it is the only path that fixes a wet roof. The choice between the two membranes is its own decision; our TPO against modified bitumen guide walks through it.
Path B: recover over the old plies
If the plies are dry and well adhered and the deck is sound, a recover keeps the old built-up roof in place as a substrate. The surface is cleaned after vacuuming, a cover board or recovery board goes down, and the new TPO or modified bitumen is installed over it. It saves the tear-off labour and the disposal of the old plies, and it keeps the building dry during the work. The trade-offs: a second roof adds weight, some manufacturers limit warranty terms on a recover, and local code allows only so many roof layers. The gravel still has to come off first; no recover goes over loose stone.
Path C: coat it and keep it
A built-up roof that is dry, sound and simply weathered can sometimes be restored with a silicone or similar coating system rather than replaced. The coating needs a clean, bare, primed substrate, so the gravel is vacuumed, the surface is power-washed and any open laps are repaired before the coating goes down. It is the lowest-cost path and the shortest-lived; it buys years, not decades. Our guide on flat roof coatings against tear-off covers when it is the right call.
Why one contractor for the removal and the roof
When the vacuum company and the roofing company are two different firms, the schedule risk lives in the handoff. The stone comes off on a Tuesday, the roofer cannot start until the following week, and the exposed plies take a rainstorm in between. One contractor carrying both stages means the roof is opened and closed on one plan, and the condition read from the removal flows straight into the roofing decision instead of being argued about later.
Talk to us
Leaders Roofing has installed, repaired and torn off built-up and modified bitumen roofs across Cook, DuPage and Lake counties since 1996, and holds an Illinois Roofing Unlimited License (#104.010248). We vacuum the gravel, read the roof underneath, and give you a priced option for each path that makes sense. Start on the gravel vacuuming and ballast removal page, or call (708) 847-5418.