Troy Commercial Roofing: TPO, EPDM, Metal & Flat Roof Replacement & Repair

A replacement, in code terms, removes every layer down to the deck. A recover lays a new roof over the old one, and the building code allows that only when the existing roof is dry and sound and has fewer than two coverings already on it. Wet insulation or a second layer means a full tear-off.

Tear-off also brings the energy code into play. When a roof with insulation above the deck is replaced, the new roof has to meet current insulation levels, and the model 2021 code asks for R-30 continuous insulation above the deck in climate zone 5A, which takes in Oakland County. A recover is exempt. While the deck is open, tapered insulation can go in to pitch water toward the drains.

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Flat roofs rarely leak in the middle of a sheet. Water gets in at laps and seams, around pipe boots and curbs, at the base of parapet walls and at drains, then travels along the deck before it shows up as a ceiling stain thirty feet away. A good repair starts by tracing the path back to the entry point, not by patching above the stain.

Single-ply seams on TPO and PVC are re-welded with hot air; EPDM laps are cleaned, primed and re-taped. Blisters, splits and punctures from foot traffic around rooftop units get cut out and covered. When the same section keeps failing, the honest answer may be replacing that section rather than patching it a fifth time.

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TPO (thermoplastic polyolefin) is the white single-ply sheet you see on most new office and retail roofs. One major maker's TPO line comes in 45, 60 and 80 mil, and the seams are fused with a hot-air welder, so the lap becomes one piece of plastic rather than a glued joint. It's made to the ASTM D6878 standard.

It goes down either mechanically fastened, with plates under each lap like the photo shows, or fully adhered with bonding adhesive. Fastened systems cost less; adhered systems sit flatter and stand up better to wind flutter. Thicker sheet buys more wear layer, so on a building you plan to hold, ask for prices on more than one thickness.

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EPDM is synthetic rubber, usually black, made to ASTM D4637. It comes in 45, 60 and 90 mil sheets that are very wide, so a roof ends up with fewer seams. Those seams are taped rather than welded, and some sheets now arrive with seam tape applied at the factory.

EPDM can be fully adhered, mechanically attached or ballasted with stone. Ballasted roofs under a 2:12 slope have to be designed to the ANSI/SPRI RP-4 wind standard, which matters on taller buildings where corner uplift is high.

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PVC is the other heat-welded thermoplastic, made to ASTM D4434. Like TPO it is usually white or light grey and welds into continuous seams, and HomeGuide's published life range for it runs 20 to 30 years. It also prices higher: about $5 to $12 per square foot installed against $4 to $10 for TPO.

Restaurants and food plants are where the choice gets specific. Grease from kitchen exhaust fans lands on the roof around the curb, and not every membrane tolerates it. Ask the roofer for the manufacturer's written guidance on grease and chemical exposure for the exact sheet being quoted, and for a containment pad under the fan.

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Standing seam metal panels can go on roofs as flat as 1/4 inch per foot; lapped, exposed-fastener panels need at least 1/2:12 with sealant in the laps, or 3:12 without. That makes standing seam the metal option for warehouses and distribution buildings with very low pitch.

Metal also has unusually good long-term data behind it. A Metal Construction Association study of 14 unpainted aluminum-zinc coated standing seam roofs, some in service for 35 years, projects more than 60 years of life for a similar roof built today. Older metal roofs with rusting fasteners and leaking end laps can often be restored with new fasteners, seam sealant and a coating instead of new panels.

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Modified bitumen is asphalt blended with rubber (SBS) or plastic (APP) polymers and built in two or more plies: a base sheet, then a granulated cap sheet. The plies go down torch-applied, mopped in hot asphalt, set in cold adhesive or as self-adhered sheets. Multiple layers give it redundancy a single-ply roof lacks, and it handles foot traffic well.

The method matters on an occupied building. Torching near wood blocking or parapets is a fire risk that self-adhered and cold-process systems avoid, at some cost in speed. HomeGuide prices modified bitumen at $4 to $7.50 per square foot installed, with a 10 to 20 year life range.

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Built-up roofing is the original flat roof: alternating layers of felt and hot asphalt or coal tar, finished with a flood coat and embedded gravel. Plenty of older commercial buildings still have one. Most of these roofs need at least 1/4 inch per foot of slope, though coal-tar systems can go down to 1/8 inch.

When a BUR roof is replaced, the code doesn't allow the old gravel to be reused, and rusted gravel stops, flashings and drain collars can't go back on either. Older built-up roofs can also contain asbestos. EPA's asbestos rule applies to commercial roofs once 160 square feet or more of asbestos-containing roofing is disturbed, and the removal method changes how it applies, so a sample before tear-off is worth paying for.

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A coating can add years to a roof that is old but still dry, for less than a new roof. The building code allows a new coating over an existing coating, metal, built-up, spray foam, modified bitumen or single-ply roof without a tear-off. HomeGuide's installed ranges are $1.50 to $4.50 per square foot for silicone and $0.50 to $3.00 for acrylic.

Two cautions. Insulation under a membrane behaves like a sponge: once it's wet, a coating on top just seals the water in, so a moisture survey should come before any bid. And the chemistry should match where water sits on your roof and what the old surface is; ask the roofer why they chose silicone or acrylic for your roof, not just which one is cheaper.

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Spray polyurethane foam is sprayed on as a liquid, rises into a seamless layer of rigid insulation, and flows around curbs and penetrations without a single lap. Thickness can be built up in low spots to improve drainage. The code wants at least 1/4:12 slope and a protective coating applied between 2 and 72 hours after the foam goes down.

That coating is the wearing surface, and it gets renewed over the roof's life. HomeGuide lists SPF roofing at $2 to $6 per square foot. Foam is weather-sensitive to install, so it's a job for the drier, warmer months.

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NRCA recommends inspecting a roof at least twice a year, in spring and fall, and after any hailstorm or severe wind. The industry test for drainage is simple: water still standing 48 hours after rain is ponding, and ponding adds weight that deflects the deck, which collects more water.

A proper inspection checks seams, flashings, curbs, drains and scuppers, and clears debris. When a roof is being sized up for recover or coating, it adds a moisture survey: infrared scanning at night, nuclear gauges or impedance meters, confirmed with small core cuts. Infrared sees heat, not water, so cores verify what the camera suggests.

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