Rooftop solar PV mounting and racking: the roofing side of an array

What rooftop solar mounting is, and the roofer's stake in it

Rooftop solar mounting, also called racking, is the structural hardware that holds a photovoltaic array on the roof and carries its dead weight and its wind load down into the building. On a pitched roof that is usually a set of attachments into the framing, rails spanning across them, and clamps that pin the modules to the rails. On a flat roof it is often a tray or rack system weighted down with ballast block. Either way, the array is a second roof sitting on top of the first one.

Here is the part the solar side underplays and the roofer cannot. The array lasts about 25 years. The attachment is a hole in the waterproofing, or a load path that the roof has to carry for that whole time. Almost every problem that comes back on a solar job traces to the roof-and-solar interface, not the panels. The panel rarely fails. The flashing around the mount fails, the membrane abrades under a rack, the deck was never checked for the load, or the array went onto a roof that had eight years left in it.

That interface is the roofer's job whether the contract says so or not, because the roofer owns the leak. This guide covers the attachment and racking side. It works alongside the membrane-selection guide for what the roof under a flat-roof array should be, and the rooftop-equipment-support guide for how anything heavy lands on a low-slope roof without crushing it.

The roof's remaining life is the decision before any other

Match the roof's remaining service life to the array's life before you talk about racking, modules, or anything else. This is the single most expensive call on the entire job, and the solar quote almost never raises it. A PV array is built to run about 25 years. If the roof under it has ten years left, you have just bolted a 25-year machine to a roof that will need to come off in the back half of the array's life.

The rule of thumb the trade runs on: if the roof has less than about five years left, re-roof first, every time. If it has five to ten years, the math almost always still favors re-roofing first, because the remove-and-reinstall cost lands inside the array's warranty window. Ten to twenty years is a judgment call on the roof's condition and how long the owner plans to keep the building. Twenty-plus years and the roof will roughly outlast or match the array, so you can mount on the existing roof.

Be blunt with the owner about this, because the solar salesman usually will not be. Putting a new array on a worn-out roof is not a savings. It is a deferred bill with interest, and the interest is the labor to lift the entire array off, re-roof, and set it back down. On a residential system that remove-and-reset alone commonly runs several thousand dollars. Re-roof first. Then mount.

Steep-slope mounting: the penetrating, flashed attachment

On a shingle roof the standard mount is a penetrating attachment, and it has four parts that stack in order. A lag screw or structural fastener bites into the rafter or truss below the deck. A standoff or L-foot sits on that fastener and lifts the rail off the roof. A flashing slides over and under the shingles to make the penetration watertight. Then a rail runs across the standoffs and module clamps pin the panels to the rail.

The fastener is the structural half and the flashing is the waterproofing half, and they have to be right independently. Land the lag in the center third of the rafter, not the edge, so the fastener develops the pull-out and shear values the racking manufacturer and the American Wood Council tables assume. Hit the edge or miss the rafter and seat into the deck only, and the attachment can pull through under wind uplift no matter how good the flashing is. Verify embedment depth against the mount manufacturer's instructions, because a lag that is too shallow has a fraction of its rated hold.

The clamp side is simple by comparison. Mid-clamps tie adjacent modules to a shared rail, end-clamps catch the last module, and both get torqued to the module and clamp maker's value. The number people skip is the rail cantilever, the overhang past the last attachment. Run the rail too far past the end standoff and the corner module becomes a lever arm the attachment was never sized for.

How is a solar roof penetration made watertight?

A solar roof penetration is made watertight by flashing it the same way you would flash any other roof penetration: the flashing has to shingle into the water path, with the upslope edge tucked under the course above and the downslope edge lapping over the course below. Water runs downhill on a roof, so a flashing that sits on top of the shingles instead of under the upslope course is a dam, not a flashing. It will leak, usually at the first wind-driven rain.

On asphalt shingle, the metal flashing should be wide enough to carry water past the penetration, commonly at least 9 inches across, and slid up under the second or third course above the lag. The mistake that causes more solar leaks than any other is not pulling the existing shingle nails before sliding the flashing up. Leave the nails and the flashing cannot seat all the way under the upper course, so it stops short and water finds the gap. Pull the nails, slide the flashing home, and let it lap correctly.

Sealant is the backup, not the waterproofing. A bead of compatible roofing sealant or butyl on the fastener and under the flashing helps, but a mount that relies on sealant alone is a future leak with a timer on it, because sealant moves, cracks, and ages while the roof has decades to go. The flashing geometry is what keeps water out. For the broader logic of flashing a penetration into the water path, the equipment-support guide covers the same principle for pipe and curb penetrations on the same roof.

Tile roof mounting: hooks and replacement tiles

Tile roofs are the hardest steep-slope mount to get watertight and the easiest to break in the process. Two methods dominate. A tile hook lags into the rafter and reaches up through a gap to support the rail above the tile, with a flashing under the course to seal the penetration. A tile replacement mount removes a whole tile and substitutes a metal flashing pan in its place, with the standoff coming up through the pan, so there is no cutting or grinding of the tile around the post.

Concrete and clay tile are brittle, and the breakage happens during install, not in service. Crew walks the field, cracks tiles underfoot, and the cracked tile leaks weeks later under the array where nobody can see it. Walk the headlap and the strong points, lift tiles to work rather than levering them, and stock spare tiles before you start because you will break some. The replacement-flashing method usually leaks less than the hook method because it puts a real flashing pan in the water path instead of threading a bracket through a gap in the tile.

Match the flashing profile to the tile. Flat, S-profile, and W-profile tile each take a different shaped pan, and a flat pan jammed under a barrel tile leaves a channel for water. Foam closures and the right profile flashing are what keep wind-driven rain from running back up under the tile around the post.

Standing-seam metal: the clamp-on, no-penetration mount

Standing-seam metal is the one roof where solar can go on with zero penetrations, and that is its big advantage. A seam clamp grips the vertical standing seam and the rail mounts to the clamp, so nothing is drilled, screwed, or cut through the panel. The S-5 clamp family is the common reference here, with different models for snap-together seams, mechanically-seamed double-folded seams, and nail-strip profiles. No hole means no flashing to fail and no leak path created by the array.

Match the clamp to the seam profile, because a clamp made for a 1.5 inch snap seam will not grip a double-folded seam, and a clamp set on the wrong profile can slip under uplift. The setscrews bear on the seam and get torqued to the clamp maker's value, hard enough to hold but not so hard they crush or pierce the seam metal on a thin-gauge panel. This is the detail that protects the metal roof's own weathertightness warranty, since the clamp does not penetrate the coating.

Through-fastened corrugated metal, the exposed-screw kind, is a different and worse case. There is no standing seam to clamp, so the mount penetrates the panel into the purlin with a gasketed, flashed fastener, and now you are back to a penetration that has to be sealed and will age. Do not confuse the two. The non-penetrating advantage belongs to true standing-seam, not to every metal roof.

Low-slope ballasted racking: weighted, non-penetrating

On a flat or low-slope commercial roof the preferred mount is ballasted, which holds the array down with weight instead of holes. The modules sit in tilted trays or on a rack, and concrete ballast blocks are loaded into the system in the quantity an engineer calculates, so gravity counters the wind that would otherwise lift the array off the roof. Nothing penetrates the membrane, which is the whole appeal: the waterproofing stays intact and there are no hundreds of flashed holes to maintain.

The weight is the catch, and it is two problems at once. The ballast plus the array is dead load the roof structure has to carry, on top of snow, and on a marginal building that load is the thing that kills the ballasted option before wind ever does. And the racking feet bear on the membrane, so they have to ride on slip sheets or protection pads, never directly on the single-ply, or thermal movement saws the rack feet back and forth across the membrane until it wears through.

Ballasted only works where the roof can carry the weight and where the wind is not so strong that the ballast count becomes absurd. On a tall building, an open exposure, or the edges and corners of any roof, the ballast needed to hold the array can exceed what the structure will take, and that is the point where the job moves to a mechanically-attached or hybrid system. The membrane-selection guide covers what the single-ply under that ballast should be, since not every membrane likes a heavy point load sitting on it for 25 years.

Mechanically-attached low-slope: flashed penetrations

When ballast cannot hold the wind or the structure cannot take the ballast weight, the low-slope array gets mechanically attached: the racking is bolted through the membrane into the deck or framing, and every one of those penetrations is flashed. This is the flat-roof version of the steep-slope penetrating mount, and it trades the ballasted system's no-holes advantage for a lighter, higher-wind-capacity system that puts dozens or hundreds of new flashings on the roof.

Each attachment usually lands on a curb, a base flashing, or a manufacturer-approved post detail that is welded or sealed into the membrane by the roofer, not just screwed and caulked by the solar crew. On a single-ply roof that means a flashed base tied into the field membrane with a target patch or a molded boot. Done by the roof manufacturer's detail, the penetration is as watertight as any pipe boot. Done as an afterthought with a screw and a glob of mastic, it is a leak waiting for the first freeze-thaw cycle.

Hybrids are common and sensible. The interior of the array is ballasted where the wind is mild, and the perimeter and corner zones, where uplift is worst, get mechanically attached to hold the edge. That puts the few penetrations where they earn their keep and keeps the bulk of the roof hole-free.

Ballasted or mechanically attached: how do you choose?

Choose between ballasted and attached by what the roof structure can carry and what the wind exposure demands, and let the engineer settle it, not the installer's preference. Ballasted wins when the roof can take the weight and the building is not in a high-wind, high-exposure spot, because it keeps the membrane intact and there is nothing to flash. Attached wins when the structure is weight-limited or the wind is strong enough that the ballast count gets unreasonable, because attachment holds the array with anchors instead of mass.

The trade-off is clean once you say it plainly. Ballast means more dead load and zero penetrations. Attachment means less load and many penetrations, each one a flashing the roof has to keep watertight for the life of the array. Neither is free. Ballast spends the structure's load capacity, attachment spends the membrane's integrity, and the right answer depends on which one the building has to spare.

Most low-slope arrays end up ballasted in the field and attached at the perimeter, because that matches the wind, which is gentle in the middle of a roof and brutal at the edges and corners. The decision lives in the structural and wind analysis, so push for that analysis before the racking is ordered, not after the ballast is on the roof.

The structural load: can the roof actually carry it?

Before any array goes up, someone qualified has to confirm the roof structure can carry the added dead load, and on a ballasted system that question can sink the whole approach. A penetrating residential array adds a modest distributed load. A ballasted commercial array adds the panels, the racking, and the concrete ballast, which together can be a few pounds per square foot spread across the roof and concentrated under the rack feet. That sits on top of the snow load the structure was already designed to hold.

This is an engineer's call, not a roofer's and not an installer's. A structural engineer reviews the framing, the deck, and the existing capacity against the added array load plus snow, and confirms it or calls for reinforcement. Do not eyeball it. A roof that has carried snow for 30 years has no spare margin you can assume, and the combination people forget is array plus ballast plus a heavy snow year landing at the same time.

The worst surprises are on older buildings and on roofs already loaded with mechanical equipment. Hedge this one hard. The structural adequacy of the roof is a question for a licensed engineer working from the actual framing and the governing building code, and the load figures the racking manufacturer publishes are inputs to that review, not a substitute for it.

How is rooftop solar designed for wind uplift?

Rooftop solar is designed for wind uplift by treating the array as a surface the wind pushes and lifts, then holding it down with enough ballast or enough attachment to resist that uplift across the whole roof. The governing analysis runs to ASCE 7, the standard for wind and other loads, which sets the wind pressures by location, building height, exposure, and where on the roof the array sits. Recent editions added dedicated provisions for rooftop solar, so the analysis is no longer a generic equipment calculation.

The number that drives the design is not the field of the roof. It is the edges and corners. Wind pressure spikes at roof perimeters and corners, often to several times the interior value, which is exactly why ballasted arrays get more ballast or switch to mechanical attachment in those zones. An array that is fine in the middle of the roof can peel up at a corner in a storm if the perimeter was designed to the interior pressure.

Ballasted systems usually lean on the racking manufacturer's wind-tunnel data rather than raw ASCE coefficients, because the tray geometry, the gaps, and the array layout change the real uplift in ways a flat-plate calculation misses. Either way, this is an engineered number. Get the wind design from the engineer and the manufacturer's tested data for the specific racking, and confirm it against the wind speed the local code adopts. Do not pick a ballast count off a chart and hope.

Protecting the membrane under the racking

Every place a ballasted rack foot touches a single-ply membrane needs a slip sheet or protection pad between the two, because the rack moves and the membrane does not like being scrubbed. The roof heats and cools daily, the metal racking expands and contracts on a different schedule than the membrane, and the foot walks back and forth a fraction of an inch with every cycle. Over years that grinds a hole in the membrane right under the array, where you find it as a leak long after the array is in the way.

The protection layer is a rubber pad, a slip sheet, or for a premium job a full separation sheet of additional membrane or geotextile fleece run under the array. It does two jobs: it spreads the point load so the foot does not press the membrane into the insulation, and it separates two materials that may not be chemically compatible. A bare aluminum or coated-steel foot sitting directly on certain membranes can also cause a compatibility problem over time, so the slip sheet is a chemical barrier as well as a wear pad.

This is also where the membrane manufacturer comes in. Most major membrane makers will issue a letter of no objection for a ballasted array on their roof, but the condition is almost always that an approved slip sheet or protection layer sits under the racking. Skip the slip sheets and you have abraded the membrane and voided the no-objection letter in one move. The membrane-selection guide covers which single-plies tolerate point loads and traffic best under an array.

Does solar void a roof warranty?

Solar can void a roof warranty, and the trigger is almost always a penetration or alteration made by someone other than the roof manufacturer's approved installer, using a method the manufacturer never blessed. Most roof warranties carry a clause that voids coverage if the roof is altered or penetrated by a third party without an approved detail. A solar crew that drills the roof, flashes it their own way, and leaves is exactly the third-party alteration that clause is written to catch.

It does not have to void anything, and on a well-run job it does not. The way you keep the warranty alive is to do the penetrations and flashings by the roof manufacturer's approved method, and on a low-slope roof to have the manufacturer's approved roofer make and warrant the penetrations, not the solar installer. On steep-slope, follow the roofing product maker's flashing detail and the racking maker's listed instructions. Get the manufacturer's sign-off in writing before the array goes up, not after a leak.

Stress this to the owner because it is real money. A voided roof warranty on a commercial building can turn a small future leak into a full uncovered repair. The flashing has to be done by an approved method, by the right party, documented, and accepted by the manufacturer. That is the difference between an array that rides on a warranted roof and an array sitting on a roof the manufacturer no longer stands behind.

Roofer and solar installer have to work the interface together

The roof-and-solar interface fails when the two trades treat it as a handoff instead of a shared detail. The solar installer knows the array, the layout, and the racking. The roofer knows the membrane, the flashing, and the warranty. The penetrations and supports live exactly between those two scopes, which is why they get done badly when nobody clearly owns them.

Coordinate before anything goes on the roof. Sit the roofer, the solar installer, and ideally the roof manufacturer's rep at the same table and settle who flashes the penetrations, by what detail, with what materials on hand, and who carries the warranty for the finished penetration. The NRCA's own position is that the owner is best served when the roofing contractor, the roof system manufacturer, and a licensed electrician are all involved in a rooftop PV install, and that the PV support and flashing components go in during the roof work, not bolted on afterward.

The cleanest jobs put the array attachments and flashings in while the roof is being installed or re-roofed, so the roofer flashes the mounts as part of the roof system. Bolting an array onto a finished roof months later, with a different crew and no manufacturer involvement, is how warranties die and leaks start.

Drainage, debris, and maintenance access between the rows

An array changes how water and debris move on the roof, and a layout that ignores drainage builds a debris dam over the membrane. Modules block sun and catch leaves, the rows trap windblown debris, and on a low-slope roof the racking can pond water against it if the array crosses the drainage path or sits over a drain. Lay the array out so water still reaches the drains and scuppers, keep it clear of the drainage path, and leave the array high enough off the roof for water and air to move underneath.

Leave room to work, too. The array has to be maintainable and so does the roof under it, which means access aisles between rows and clear paths to the drains, the flashings, and the rooftop equipment. An array packed wall to wall with no aisles means the next leak under it cannot be reached without pulling panels, and the roof inspection that the warranty depends on cannot happen.

Plan the service path with walk pads where crews will actually walk, so foot traffic during cleaning, repair, and electrical work lands on protection instead of bare membrane. The equipment-support and walkway guide covers laying out that walk path and protecting the membrane at traffic, which matters more once an array gives crews a reason to be on the roof regularly.

Every penetration is a leak path: keep the count honest

Count the penetrations, because each one is a place the roof can leak and the total adds up fast on a large array. A residential shingle system might land a few dozen flashed lags. A mechanically-attached commercial array can put hundreds of penetrations through the membrane. Every one of them is a flashing that has to be made right and stay right for 25 years, and the leak risk scales with the count.

The discipline is twofold: minimize the count where the design allows, and flash every remaining one properly. A ballasted system trades penetrations for weight and gets the count to near zero. A standing-seam clamp system gets it to actual zero. A penetrating system cannot avoid holes, so the answer there is to flash each one by the approved method and document it, not to reduce quality to save time across a hundred mounts.

When a solar roof leaks, the leak is at a penetration far more often than in the field of the membrane, the same as any roof. That is the first place an inspector looks and the first place you look. Treat the penetration count as a risk number, and treat each flashing as if it is the one that will leak, because statistically one of them is.

Re-roofing under an existing array is the nightmare

Re-roofing a roof that already has an array on it is the situation the roof-life-first rule exists to prevent, and once you are in it there is no cheap way out. The entire array has to come off so the roof can be torn off and rebuilt, then the array goes back up, gets re-flashed, re-wired, and re-commissioned. You are paying solar labor to dismount and remount a whole system on top of the roofing cost, plus the risk that modules and racking get damaged in the handling.

On a residential system the remove-and-reset alone commonly runs into several thousand dollars before a single shingle is touched. On a commercial ballasted array it means unloading and restacking tons of ballast, lifting the trays, re-roofing, and rebuilding the array, with the building's power production down the whole time. The cost is not a rounding error. It is often a meaningful fraction of what the array cost in the first place.

This is the lesson behind the whole guide. The reason you check the roof's remaining life first, before you talk about racking, is that getting it wrong sentences the owner to this exact job inside the array's life. Re-roof first when the roof is close, and you never meet this nightmare. Skip that step and you will.

Grounding, bonding, and dissimilar metals on the roof

The array has to be grounded and bonded so a fault has a path back and the metal frames sit at the same potential, and the way that gets done interacts with corrosion on the roof. The common hardware is the WEEB, a washer with sharp teeth that bites through the anodized coating on the aluminum module frame and rail when torqued, bonding the parts electrically, paired with a lay-in lug that lands the equipment grounding conductor. This is the electrician's scope, but it lands on the roofer's roof, so the interface matters.

Mixing metals on a roof that sees rain and condensation is where galvanic corrosion starts. Aluminum racking, stainless fasteners, coated-steel feet, and a copper ground wire are several dissimilar metals in one assembly. Run a bare copper ground conductor in direct contact with aluminum rail and the aluminum pits and corrodes at the contact, and within a couple of years the bond can corrode through and open the ground path entirely. The stainless WEEB or a listed bonding lug is what keeps the copper off the aluminum.

Use the racking and bonding hardware the manufacturer lists together, in the metals it specifies. Stainless fasteners into aluminum, listed bonding washers at the frame, and a lug rated for the conductor metal. The corrosion failures on the roof are not in the field of the membrane. They are at the connections, the same as the leaks.

Fire setbacks, access pathways, and rapid shutdown

Rooftop solar has to leave the fire service room to work the roof, and those setbacks and pathways are fire-code requirements, separate from the electrical code. The layout rules, the clear pathways and ridge setbacks, come from the fire code, the International Fire Code and NFPA, while the electrical rapid-shutdown rule comes from the National Electrical Code at Article 690. Two different code bodies govern two different parts of the same array, and the array layout has to satisfy both.

The pathway and setback figures vary by adopted code and jurisdiction, but the common pattern is a clear pathway from eave toward ridge on roof planes with panels and a clear setback at the ridge so firefighters can cut a ventilation hole and move on the roof. On many residential layouts that means leaving a clear path and a ridge setback rather than filling the plane edge to edge. Rapid shutdown, under NEC 690.12, requires the array to drop to a safe voltage quickly so firefighters are not facing an energized roof.

These are code calls, so confirm the actual dimensions and the rapid-shutdown requirement against the adopted fire code, the adopted NEC edition, and the local fire marshal before the layout is fixed. The setbacks affect how many modules fit, so they belong in the layout from the start, not as a redesign after the fire marshal red-tags the plan.

Commercial versus residential: which mount goes on which roof

The two worlds split cleanly along roof type. Residential solar lives mostly on steep-slope shingle, tile, and standing-seam roofs, so the residential mount is usually a penetrating, flashed attachment into the rafters, or a non-penetrating clamp on standing-seam. Commercial solar lives mostly on low-slope single-ply roofs, so the commercial mount is usually a ballasted rack or a mechanically-attached system, and the conversation is about load and wind rather than rafter location.

The large commercial and data-center case pushes everything harder. A big low-slope array spreads tons of ballast or hundreds of penetrations across acres of roof, and the structural load review and the wind analysis stop being formalities. On a data center the roof also carries heavy mechanical equipment already, so the array competes for the same structural margin, and the coordination between the roofer, the solar engineer, and the structural engineer is the job, not a courtesy.

Use the roof type to pick the starting mount, then let the structure, the wind, and the warranty narrow it. The map below is the quick version of where each method belongs.

What an inspection of a solar roof actually checks

An inspection of a roof with an array on it goes to the same places leaks come from, in order. The flashings at every penetration come first, because that is where the water gets in. On a ballasted roof the inspector checks the slip sheets and looks for abrasion or displaced ballast under the racking. On an attached roof the inspector checks the base flashings for splits, fishmouths, and failed seals. The field of the membrane comes last, the same as any roof inspection.

The structural and wind items get a look too. Is the ballast still where the engineering put it, or has it been moved or shed. Are the attachments tight and the rail clamps torqued, or has anything backed out under cycling. Is the array still clear of the drains and the drainage path, or has debris built a dam against it. And is the bonding intact, or has a corroded connection opened the ground path.

Keep the array accessible enough that this inspection can happen, because a warranty inspection that cannot reach the flashings is a warranty inspection that does not get done. The first thing the inspector wants to see is the penetration detail and the record that says who flashed it and by what method.

What to document

The record on a solar roof is what answers the leak call and the warranty claim later, and it has to tie the array to the roof, not just to the electrical system. Capture the roof type and its remaining life at the time of install, the mount method, who made and flashed the penetrations and by what approved detail, the structural and wind analysis and who stamped it, the membrane manufacturer's no-objection letter or warranty acceptance, and the slip-sheet or protection-pad detail under any ballasted racking.

If the roof was re-roofed before the array went on, record that, because it is the single fact that tells the next owner the array and roof life were matched on purpose. Write down the flashing method and the manufacturer sign-off in the same place, so when a leak shows up the question of who owns it has an answer instead of a fight.

Common mistakes

• Putting a 25-year array on a roof with under ten years left instead of re-roofing first.
• Flashing a penetration on top of the shingles instead of lapped under the upslope course.
• Leaving the existing shingle nails so the flashing cannot seat under the upper course.
• Skipping the structural load review and assuming the roof can carry the array plus ballast plus snow.
• Under-designing for wind uplift, especially at the roof edges and corners.
• Running ballasted racking feet directly on the membrane with no slip sheets, abrading it.
• Penetrating or altering the roof by an unapproved method and voiding the roof warranty.
• Laying the array across the drainage path so it dams water and traps debris.
• Landing lag screws at the rafter edge or into the deck only, so the attachment can pull through.

Field checklist

Standards and references

The racking manufacturer's instructions are the first reference on any solar mount, because they carry the listed flashing detail, the attachment spacing, the embedment depth, and the tested wind and load values for that specific system. Install outside those instructions and you have voided the racking listing and usually the warranty with it. The flashing and attachment system is only rated as installed per the maker's detail.

The structural load and the wind design run to ASCE 7, the standard for minimum design loads, whose recent editions added provisions specific to rooftop solar. Treat the load and wind numbers as engineered values from a licensed engineer working to the governing building code and the racking maker's tested data, not as something to read off a chart. The structural adequacy of the roof is an engineer's call against the actual framing.

On the roof side, the roof system manufacturer's requirements and the NRCA guidance govern the penetration and the warranty. The NRCA publishes guidance for rooftop-mounted PV and holds that the roofing contractor, the roof manufacturer, and a licensed electrician should all be involved, with the PV flashings installed as part of the roof work. The fire-code setbacks and access pathways come from the adopted fire code, the IFC and NFPA, and the rapid-shutdown requirement from NEC Article 690, specifically 690.12. The exact dimensions and code provisions shift by edition and jurisdiction, so confirm them against the codes the AHJ has actually adopted, and let roof-life-first and proper flashing carry the decisions the codes do not spell out.

Units and terms

Rooftop solar mounting borrows terms from both the roofing trade and the solar trade, and the same part goes by different names on the two sets of drawings.

Racking and mounting both mean the structural hardware holding the array. A standoff, L-foot, or stanchion is the attachment that lifts the rail off the roof on a penetrating mount. Ballast is the concrete weight that holds a non-penetrating low-slope array down. A slip sheet or protection pad is the layer between a rack foot and the membrane. Dead load is the static weight of the array and ballast on the structure, measured in pounds per square foot. Wind uplift is the suction the wind puts on the array, designed to ASCE 7. A WEEB is the toothed bonding washer that grounds the metal frames.

Racking / mounting

The structural hardware that holds the PV array on the roof and carries its load into the structure

Standoff / L-foot

The attachment on a penetrating mount that lifts the rail off the roof above the flashing

Ballast

Concrete weight that holds a non-penetrating low-slope array down against wind uplift

Slip sheet / protection pad

The wear-and-compatibility layer between a ballasted rack foot and the roof membrane

Dead load

The static weight of the array plus ballast on the structure, in pounds per square foot

Wind uplift

The suction wind exerts on the array, designed to ASCE 7, worst at edges and corners

WEEB

Washer for electrical equipment bonding; teeth bite the frame coating to bond the array

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