Commercial Roofing Questions in Elizabethtown

A commercial roofing contractor installs the full roof assembly on a low-slope building, from the insulation on the deck up to the membrane, flashing and perimeter metal. Each layer has a job.

On a metal building, the same job means panels, clips or screws, ridge cap, eave trim and closures over the purlins.

Roof slope, rooftop traffic, and what lands on the roof from inside the building decide which system fits. Low-slope roofs take a membrane, and pitched roofs on steel framing usually take metal panels.

A roof walk and a core cut showing the deck and insulation narrow the choice to one or two systems.

Edges, curbs and drains decide more than the field membrane does, since most water problems start where the roof changes direction. A clean install at those points matters more than which brand covers the middle.

Details to look at on any new roof:

• Perimeter edge metal and its cleat, which resist wind peeling the roof back
• Parapet coping, with joints sealed and sloped toward the roof
• Curb flashing at rooftop units and exhaust fans, run high enough above the finished surface
• Roof drain clamping rings and sumps set low enough that water reaches them
• Pipe boots and pitch pans around conduit, gas lines and supports

Photos of these details at the end of the job make later inspections easier.

The deck, the existing layers and the drainage are checked first, because each one limits which roof can go on. A core cut through the old roof shows how many layers exist and whether the insulation is wet.

The roof walk covers:

• Deck type, such as steel, concrete, wood plank or gypsum
• Standing water lines and stains around drains and scuppers
• Height of curbs, door thresholds and wall flashing above the roof
• Rooftop units, ductwork and conduit that have to be lifted or worked around
• Building use under the roof, such as cold storage, food processing or open warehouse space

Those findings set the system, the insulation thickness and the edge details before any material is ordered.

TPO is a single-ply thermoplastic membrane, usually white, that rolls out in wide sheets and gets heat-welded at every seam. It is a common choice on warehouses, retail centers, offices and light industrial buildings with flat or low-slope roofs.

The membrane goes over insulation and a cover board, then turns up curbs, walls and parapets as flashing. Pre-formed corners, pipe boots and curb wraps made from the same material keep the details consistent with the field.

White TPO reflects sunlight, so it suits buildings that run air conditioning through the summer. It is also used on recovers, where a new TPO layer goes over an existing roof that is dry and well attached.

Hot-air welding joins TPO seams, with a machine melting the two overlapping sheets together into one piece of plastic. Once cooled, the weld is part of the membrane instead of a glued joint.

Each seam gets probed with a blunt tool after welding to find any gap or cold spot. Crews also cut small test welds at the start of each day and pull them apart to confirm the welder settings.

Weld quality depends on dry, clean membrane. Dew, dust and old membrane that has weathered all affect the weld, so crews wipe and prep the lap area first. On a TPO roof, a seam that peels open later almost always traces back to a weld made too cold, too fast or over a dirty lap.

The deck type, the wind exposure and the roof edge height decide how a TPO roof is held down. Each method has a clear use.

Ballast is more common with EPDM than TPO. Corner and perimeter zones get tighter fastener spacing or full adhesion, since wind pulls hardest there.

A white TPO roof reflects much of the sun's heat, so the roof surface stays cooler and less heat moves into air-conditioned space under it. The U.S. Department of Energy's Guide to Cool Roofs explains this through two ratings, solar reflectance and thermal emittance.

Owners can compare membranes in the Cool Roof Rating Council directory, which lists rated roof products.

Where the gain shows most:

• Cooled warehouses and retail space with large, open roofs
• Offices with ductwork running just under the deck
• Buildings with thin insulation over a steel deck

Dirt on the membrane lowers reflectance, so walking the roof and rinsing heavy buildup around rooftop units keeps the surface working as built.

TPO flashing runs up each curb, wall and parapet as a separate welded piece, then gets terminated with a metal bar or counterflashing so water stays out from behind it. Every flashing seam is welded the same way as the field.

Common details on a TPO roof:

• Rooftop unit curbs wrapped with membrane and pre-formed outside corners
• Walls finished with a termination bar and sealant, or metal counterflashing
• Drains clamped with a ring that pinches the membrane into the drain body
• Scuppers lined with a membrane sleeve through the parapet

Walkway pads go along the service path to each rooftop unit, so technicians stay off the open field membrane.

EPDM is a synthetic rubber membrane, usually black, that comes in large sheets so a roof can be covered with fewer seams. It stays flexible in cold weather, which suits Kentucky winters with frequent freeze-thaw swings.

EPDM fits big, simple roofs with few penetrations, such as storage buildings, older plants, schools and churches with flat sections. It also fits recover work, where the new sheet goes over a dry existing roof and a new cover board.

The rubber stretches as the building moves, and the large sheets cut the number of field seams on the roof. Curbs, drains and walls still need flashing made from cured or uncured EPDM pieces.

Seam tape and primer seal EPDM seams instead of heat. The crew cleans and primes both sides of the lap, presses the tape between them, and rolls the seam with a hand roller to set the bond.

Seam steps in order:

1. Scrub the lap area clean of dust and talc.
2. Prime both mating surfaces with the tape maker's primer.
3. Place the seam tape and remove the release paper.
4. Roll the lap firmly toward the edge.
5. Cap the seam ends and T-joints with a cover patch.

Taped seams hold well when the primer has flashed off and the surfaces are dry. Seams laid over damp primer or dirt are the ones that open later.

Black EPDM absorbs sunlight, so the roof surface runs hotter in summer and gives up less heat to the sky in winter. Whether that suits a building depends on how it is used and cooled.

The DOE Guide to Cool Roofs notes that a reflective roof gives up a little winter solar warming, so the choice weighs both seasons. White-on-black EPDM is also made for owners who want rubber with a reflective face.

EPDM is held down three ways: fully adhered with bonding adhesive, mechanically fastened with plates through the laps, or ballasted with river stone or pavers.

Fully adhered EPDM over a cover board makes a smooth, wind-resistant roof and suits roofs with lots of rooftop units. Mechanical fastening goes quickly on steel decks. Ballast needs a structure built for the added weight and a parapet high enough to keep the stone in place.

Edge metal and parapet flashing matter on every method. Wind lifts EPDM at the perimeter first, so the edge cleat, the fastening rows near corners and the flashing at parapet caps are installed to the system maker's wind requirements.

Hail rarely cracks EPDM, because the rubber bends under impact and the cover board underneath takes much of the force. Sharp debris and dropped tools are the bigger threat, since a puncture opens a hole straight through the sheet.

Ways to protect a new EPDM roof:

• Walkway pads on the paths to rooftop units, hatches and ladders
• A cover board under the membrane instead of bare insulation
• Thicker or reinforced sheet on roofs with heavy service traffic
• Clean-up of screws and metal shavings after every rooftop unit service call

After a hailstorm, walk the roof and look for cuts near metal edges and dents in the insulation under the sheet, which feel soft underfoot.

Industrial roofs cover larger areas, carry heavier equipment and catch whatever the process inside sends up through stacks and vents. That changes the membrane choice, the insulation strength and the way crews work around the building.

Common industrial roof features:

• Exhaust fans and process stacks that leave oil, grease or dust on the membrane
• Heavy rooftop units on raised curbs or steel frames
• Long drainage runs to interior drains or scuppers
• Skylights and smoke vents spread across the field
• Frequent maintenance traffic from plant staff

Industrial roofs often need higher-density insulation or a cover board rated for foot traffic, plus walkway pads routed to every service point.

PVC and other oil-resistant membranes hold up better near grease, oils and chemical exhaust than standard EPDM or TPO, which can swell or soften when those residues sit on them. The membrane maker's chemical resistance chart settles the question for a specific process.

Approaches on industrial roofs:

• Oil-resistant membrane across the whole roof where exhaust is widespread
• Sacrificial pads or a separate membrane zone around one grease exhaust
• Grease containment boxes at kitchen or process fans
• Metal curb caps and drip edges that keep residue off the field

A roof walk with the plant's maintenance staff identifies which stacks run hot, which vent oil mist, and which sit idle.

Drainage on an industrial roof is planned around how far water has to travel and where it can leave the building. Large roofs usually combine more than one outlet type.

Tapered insulation and crickets steer water to each outlet so the field drains dry after rain.

Most plants keep running during a roof replacement because the work goes in sections, with each area torn off and dried in before the crew leaves. Planning with plant staff sets the order.

Items to schedule with the plant:

• Shutdowns of rooftop units and makeup air intakes near the active area
• Protection over production lines under any deck repairs
• Crane or lift days for heavy equipment and material loading
• Fire watch and hot work rules if torches or welders run on the roof
• Clear routes for crews that stay away from forklift lanes

Each day ends with the new section tied into the old roof with a temporary seal, so overnight rain stays outside.

Tapered insulation is a set of boards cut with a built-in slope that pushes water toward drains and scuppers on a roof whose deck is nearly flat. It is laid over the base insulation in a pattern drawn for that roof.

Large flat roofs collect water in low spots between drains, around rooftop unit curbs and along walls. Tapered layouts fix those patterns with:

• Main slope toward each drain or scupper
• Crickets on the high side of curbs and chimneys
• Saddles between drains to break up flat valleys

The added thickness raises the roof surface, so curb heights, wall flashing and door thresholds get checked before the layout is final.

Standing seam fits buildings that need concealed fasteners and a longer-term roof, while R-panel fits pole buildings, shops and warehouses where cost and quick installation lead. Both use painted steel panels.

Both need ridge caps, eave trim and closures installed to the panel maker's details. Panel gauge and paint finish, such as PVDF or SMP, follow the purlin span, the foot traffic expected and how long the color has to hold.

A metal roof can go over an existing flat roof by installing retrofit framing that creates slope, then fastening new panels over that frame. The old roof stays in place underneath, and water sheds off the new pitched surface.

The retrofit work involves:

• Checking the structure for the added weight of framing and panels
• Setting light-gauge steel framing or sub-purlins on the existing roof
• Adding insulation inside the new attic space if wanted
• Building new eave gutters, rake trim and wall flashing at the edges

Rooftop units need new curbs that extend through the panels. An engineer's review is the usual first step, since the frame transfers load to the original structure.

Repairs on an existing commercial metal roof center on fasteners, damaged panels, end laps and the flashing at curbs and walls, since those are the places water gets past the steel. Every repair uses parts that match the panel profile already on the building.

Once repairs keep spreading across the field of the roof, a new metal roof or a retrofit over the old one becomes the next step.

A commercial metal roof stays watertight longest with a look twice a year and after hail or high wind, because loose screws, clogged gutters and cracked sealant are small jobs when caught early.

Maintenance tasks on each visit:

• Clearing leaves and silt from gutters, valleys and downspouts
• Removing branches and debris from the panels
• Tightening or replacing loose and rusted fasteners
• Resealing pipe boots, curb flashing and trim joints
• Checking ridge caps, eave trim and closures after wind

In central Kentucky, the fall visit clears gutters and valleys before leaves pile up and winter ice forms at the eaves. Photos from each visit show how the roof is changing year to year.

Condensation forms when warm, moist air inside meets the cold underside of steel panels, so new metal roofs on shops and storage buildings need insulation or a vapor retarder under the panels. The choice depends on how the building is heated and used.

Common methods on new metal buildings:

• Faced blanket insulation draped over purlins before panels go on
• Rigid insulation between the panels and the deck
• Spray foam on the underside of the panels after installation
• Ridge vents and closures that move moist air out
• Synthetic underlayment over a solid deck, which also backs up laps at eaves and valleys

Uninsulated panels over a heated shop or a livestock area drip on cold mornings. Planning insulation before the panels go on costs less than adding it later.