Commercial Roofing

Built-up roofing is the original low-slope system: alternating plies of felt and bitumen built into a laminated membrane, usually surfaced with gravel. It is redundant by design and repairs well, and it is heavy, slow to install, and hot and odorous to build.

Modified bitumen took the same asphalt chemistry and added polymer modifiers — SBS for flexibility in cold, APP for heat resistance — delivered in rolls that are torched, mopped, cold-applied, or self-adhered, typically as a base sheet and a cap sheet. It keeps the multi-ply redundancy of BUR with far less field labor.

Single-ply is the modern default. EPDM is a synthetic rubber sheet that has been proven in the toughest climates for over thirty years, and it handles temperature extremes and UV about as well as anything on the market. TPO is a thermoplastic sheet, typically white and highly reflective, and it is the fastest-growing product in commercial roofing. PVC is the other thermoplastic, chosen where the roof sees grease, chemicals, or restaurant exhaust, which degrade other membranes.

Duro-Last is prefabricated PVC. The panels and flashings are fabricated in the plant to the building’s measured dimensions and pre-welded there, so a large share of the seam work is done under factory conditions instead of on a windy roof, and rooftop labor drops accordingly.

The difference between the thermoplastics and EPDM comes down to the seam. TPO and PVC are hot-air welded: the two sheets fuse into a single homogeneous mass, and a properly made weld is generally stronger than the sheet on either side of it. EPDM sheets are joined with primer and seam tape — a bond that works well when the surfaces are clean and correctly primed, and which has historically been the weak point of the system when they are not. Neither is disqualifying; it just means EPDM quality lives in seam prep and thermoplastic quality lives in weld temperature and technique, and both are checked by probing seams after they cool.

• Mechanically attached. Fasteners and plates through the membrane along the seam lines, covered by the next sheet. Fast and economical, and the membrane flutters under wind uplift, which drives more air movement into the assembly.
• Fully adhered. Bonding adhesive across the entire field. Best wind uplift performance, the smoothest finished appearance, and the most sensitive to substrate condition, temperature, and moisture at the time of install.
• Ballasted. Loose-laid membrane held down by river rock or pavers. Inexpensive and quiet, and it adds substantial dead load, makes leak location difficult, and performs poorly in high-wind zones.

Positive drainage means the roof sheds standing water within about forty-eight hours of rainfall. Water that stays past that adds real dead load — roughly five pounds per square foot for every inch of depth over the ponded area — accelerates membrane weathering, grows biological matter, deposits dirt that defeats a reflective roof, and voids most manufacturer warranties.

The fix is rarely the membrane. It is tapered polyiso insulation built into a slope, usually an eighth or a quarter inch per foot, with crickets between and behind drains to move water rather than trap it, plus adequate drains, overflow scuppers, and clear sumps.

Energy code sets a minimum roof insulation R-value by climate zone, and a reroof is usually the moment a building has to meet the current one. Polyisocyanurate is the common choice at roughly five and a half to six R per inch. Two staggered layers outperform a single thick layer, because the offset joints break the thermal bridging that runs straight through aligned seams. A cover board over the insulation protects the membrane from foot traffic and improves hail performance, and it is the cheapest durability upgrade available on a commercial roof.

Elastomeric, silicone, and acrylic coating systems can restore a roof that is fundamentally sound: the membrane is watertight or repairable, the seams and flashings can be reinforced, and — this is the part that decides it — the insulation underneath is dry. Core cuts or an infrared scan answer that question. A restoration re-establishes a reflective, monolithic surface, extends service life, carries its own warranty, and avoids the disruption and disposal of a tear-off entirely.

When the insulation is saturated, a coating is money spent sealing water inside the assembly, where it keeps destroying the deck and keeps costing you in energy. That roof needs a tear-off, and being told so is more valuable than being sold a coating.

On an occupied building the schedule is set by the tenants, not the crew. Tear-off is loud directly below, and torch and hot-asphalt work carries odor into the return air unless intakes are managed. Work gets staged so no section is left open at the end of a shift, sequenced around business hours and around whatever is happening under that specific bay, and coordinated so egress routes, fire lanes, and parking stay usable. Interiors below active work get protected, and crane and material staging gets planned against the tenant’s dock and traffic patterns rather than against ours.