Low-slope and metal assemblies
Commercial Roof Systems We Install, Dallas
Five assemblies, five sets of tradeoffs. This page covers how each one is built, how it fails, and which buildings it belongs on.
Every assembly on this page is chosen for the deck under it, not the other way around.
Five assemblies, and what actually separates them
Every system on this page keeps water out. What differs is how each one gets there, what it costs to put down, how it behaves once something goes wrong, and how many years it returns before the conversation starts over. Those differences are not preferences. They come out of the deck you have, the amount of equipment on the roof, how much of the field is open, whether the roof drains, and how long you intend to own the building.
Deck type narrows the list first. A steel deck takes a fastener and opens up every mechanically attached option. Gypsum, cementitious wood fiber and lightweight concrete decks will not hold one reliably, which pushes the work toward adhered assemblies and moves the price before anything else gets discussed. Structural capacity narrows it next, because a stone-surfaced asphalt roof weighs several times what a thermoplastic sheet over board weighs.
After that it comes down to what happens on the roof. A field carrying forty penetrations with a service technician on it every week is a different problem than a distribution building nobody visits. Puncture resistance, ease of detailing, and what it costs to flash a curb start to matter more than the price per square foot of sheet, and the assembly that looked cheapest on paper stops being the cheapest one installed.
Comparison
Service life in North Texas, assembly by assembly
The ranges below are what these systems return on buildings in this region, not what a data sheet promises under ideal conditions. Hail, ultraviolet load and a hundred-degree annual swing age all of them faster in this region than the same materials age in a mild climate, so a realistic expectation sits in the lower half of each range unless the roof drains and gets looked after.
| Assembly | Construction | Expected life |
|---|---|---|
| TPO and PVC single-ply | A thin thermoplastic sheet whose joints are fused with hot air rather than bonded with adhesive, which means every joint can be tested with a probe after it is made. | 15 to 25 years |
| Modified bitumen | Asphalt sheets stiffened with a polymer and laid in overlapping plies. Tough underfoot, and straightforward to detail where the roof is full of penetrations. | 15 to 20 years |
| Built-up roofing (BUR) | Courses of felt bedded in bitumen and finished with aggregate or a surfacing sheet. It is heavy, slow to install, and slow to fail. | 20 to 30 years |
| Standing-seam metal | Long panels joined at a raised seam that sits above the water, carried on clips that let the metal grow and shrink as temperature swings. | 30 to 40 years |
| Coatings and restoration | A fluid-applied layer that cures into a new weathering surface over an assembly which is structurally intact and dry. It extends service life and repairs nothing beneath it. | 10 to 15 years |
What pushes a roof to the bottom of its range
Standing water is the largest single variable and it is not close. A roof still holding water forty-eight hours after a rain is aging in those spots at a rate the rest of the field never sees. Membranes soften, laps stay wet, dirt and biological growth build up in the low areas, and any water-based coating sitting in a pond is on its way out. Slope gets corrected with tapered insulation and added drainage, and that correction belongs inside the scope of a replacement rather than on a list of things to look at later.
Rooftop traffic is the second. Most rooftop punctures are made by somebody who was not a roofer: a technician servicing a unit, an installer running conduit, a contractor who set a satellite mount and caulked around the bolts. Pads placed on the routes people genuinely use, plus a rule that any vendor who fastens something to the roof has to report it, removes most of that risk for very little money.
Then there is whether anybody looks. The roofs that reach the top of their range are the ones where drains got cleared twice a year, a split lap got welded in the season it opened, and somebody went up after the hail instead of waiting for a ceiling stain. None of that is expensive, and all of it is the difference between the two ends of every row in the table above.
Common questions
Which system is right for a Dallas warehouse?
On a steel deck with a wide open field and little rooftop equipment, welded thermoplastic single-ply is usually the lowest cost per year of service, and the reflective surface helps with a long cooling season. If the building ponds badly and the frame will carry it, retrofit metal framing is the option that solves drainage instead of managing it. Cores and a walk decide between them.
How do we find out what is already on our building?
A core cutter answers it in about ten minutes. The plug comes out as a stack: every covering that has been installed, the board beneath each one and how thick it is, whether that board is dry, and the material of the deck at the bottom. Several plugs spread across the field describe the whole building instead of one corner of it, and every plug gets patched the same day it is pulled.
Can a new system go over the old one?
Sometimes, and the conditions are narrow. Cores have to show a single covering already in place, dry board underneath it, a surface even enough to receive new material, and a frame with capacity to spare. Miss any one of those and a recover buries a problem rather than solving it. The longer version of that discussion sits on the replacement page.
Do you install all five of these?
Yes, and we would rather talk you out of the wrong one than sell you the one we happen to prefer. Different buildings genuinely need different assemblies, and a contractor who recommends the same system to every caller is describing their own crew rather than your roof.