A cobertura de um edifício com estrutura de aço pode suportar painéis solares? Um guia completo de engenharia e compras para compradores B2B

Why This Question Matters for B2B Buyers

Across Southeast Asia, the Middle East, Africa, Latin America, and Europe, industrial and commercial electricity prices continue to climb while photovoltaic module prices keep falling. As a result, more factory owners, logistics developers, and trading companies are asking a very practical question before they sign a steel structure building contract: can the roof of a steel structure building carry solar panels?

For a B2B buyer, this is not a technical curiosity. It is a procurement decision with real financial consequences. A warehouse or workshop roof is often the largest unused surface a company owns. Covering it with photovoltaic modules can reduce grid electricity bills, stabilize energy costs over the long term, and support corporate sustainability targets that increasingly appear in customer requirements and tender documents. But if the roof structure is not designed or assessed for the additional loads, a rooftop solar project can turn into a costly retrofit, a warranty dispute, or in the worst case a structural safety problem.

This guide explains, in engineering and procurement terms, when a steel structure building roof can carry solar panels, what loads are involved, which roof and mounting combinations work well, how costs and timelines are affected, and what questions a buyer should ask before committing to a project. It is written for procurement managers, project engineers, EPC contractors, and developers who are evaluating either a new pre-engineered steel building with a future solar plan, or a retrofit of an existing metal roof.

The Short Answer: Yes, in Most Cases — With Conditions

The straightforward answer is that most modern steel structure buildings can accept rooftop solar, provided the roof structure is properly designed or assessed for the additional load, and the mounting system is matched to the actual roof type. Steel is a strong candidate for solar integration because a typical pre-engineered steel building distributes roof loads through purlins to rigid frames spaced at regular bay distances, and the framing itself usually has reserve capacity beyond the original design envelope when loads are modest and well planned.

However, the words "in most cases" carry weight. The additional weight of modules, rails, and mounting hardware is only part of the picture. Wind uplift on tilted arrays, snow accumulation behind panel rows in cold regions, corrosion risks around fixings, drainage interference, and the condition of an aging roof all change the answer. A roof that works perfectly as a weather enclosure may still need reinforcement, or a different mounting strategy, before it becomes a solar platform.

That is why the smartest approach for a buyer is to treat solar readiness as a design input, not an afterthought. When a buyer tells the steel structure supplier at the quotation and design stage that a rooftop photovoltaic system is planned, the frames, purlins, and roof system can be specified with the additional load already included, usually at a modest marginal cost compared with a later retrofit.

Understanding Roof Loads on a Steel Structure Building

To judge whether a roof can carry solar panels, it helps to understand the load categories used in structural steel design. Every roof is designed for a combination of loads, and a photovoltaic system is added to that combination rather than replacing it.

Dead Load

The dead load is the permanent weight of the building itself: steel frames, purlins, roof panels or sheets, insulation, fasteners, and any fixed equipment. A typical single-layer corrugated steel roof on cold-formed purlins is light compared with concrete roofs, which is one of the reasons steel buildings are attractive for solar: the structural system already carries relatively little permanent weight, leaving usable capacity for additional equipment such as photovoltaic arrays.

Live Load and Collateral Load

The live load represents temporary loads such as maintenance workers and light tools moving on the roof, and it is defined by the applicable building code for the project location. The collateral load, sometimes called superimposed dead load, covers permanent additional equipment that is not part of the primary structure: suspended services, sprinkler piping, ceilings, and increasingly, rooftop photovoltaic systems. When a solar array is planned, it is normally treated as part of the collateral load, which means the design engineer adds its weight to the permanent loads the frames and purlins must carry for the life of the building.

How Much Weight Does a Rooftop Solar System Add?

For planning purposes, a conventional tilted or flush-mounted photovoltaic system on a metal roof typically adds a distributed load in the rough range of 12 to 17 kilograms per square meter of roof area covered, including modules, rails, and mounting hardware. Heavier systems, such as ballasted mounting on flat or low-slope roofs, can add considerably more because they rely on concrete blocks for stability instead of mechanical fixings. These figures are planning references only: the actual load depends on module type, rail spacing, mounting method, and the project's wind and snow conditions, and the final values must come from the system supplier's structural calculations and the project engineer's verification.

The key procurement insight is that this range is usually small relative to the total design load of a properly engineered steel roof, especially when the building was designed with some reserve. But small does not mean negligible at every point: the load is not applied evenly. It concentrates at attachment points, along rail lines, and at ballast positions, so the checking that matters is done at the purlin and fastener level, not just at the whole-roof average.

Wind Uplift: Often More Critical Than Weight

Many buyers assume weight is the main structural question, but for tilted photovoltaic arrays, wind is frequently the controlling case. A tilted panel behaves like a small wing: wind passing over and under it creates uplift and pressure forces that transfer into the roof through the mounting system. In coastal regions exposed to typhoons or in open terrain with high design wind speeds, the anchorage of the array can govern the design of the attachment details, and may even influence the purlin spacing chosen for the building. This is a further reason why solar plans should be declared early: the supplier can orient bays, adjust purlin gauges, and design attachment zones with the wind case in mind.

New Buildings Versus Existing Buildings

The answer to the solar question differs significantly depending on whether the buyer is commissioning a new steel structure building or evaluating an existing one.

Designing a New Building with Solar in Mind

For a new pre-engineered steel building, integrating a photovoltaic plan at the design stage is by far the most efficient path. The buyer or EPC contractor communicates the intended solar layout, the approximate technology, and the target coverage area. The supplier then includes the photovoltaic collateral load in the frame and purlin design, verifies the anchorage zones for wind uplift, and can select a roof profile that suits the preferred mounting method, for example a standing seam profile that allows non-penetrating clamps.

The marginal cost of this approach is usually a small fraction of the total building cost, because steel sections are already being specified and small increases in gauge or mass are efficient. The buyer gains a roof that is certified for the solar system from day one, clean warranty conditions, and no construction disruption later.

Assessing an Existing Steel Roof for a Retrofit

For an existing building, the process starts with an assessment rather than an assumption. A competent assessment typically covers: the original design documents and load basis, if available; the age and condition of the roof sheets, purlins, and fasteners; visible corrosion, deformation, or previous leaks; the actual purlin spacing and section; the condition of the foundation and frames as observed; and the local wind and snow environment. Where documents are missing, a simple load test or additional verification may be recommended by the engineer.

In many cases the assessment concludes that the existing roof can accept a light, well-distributed photovoltaic system with appropriate fixing details. In other cases the engineer will recommend either a partial reinforcement of specific purlin lines, a reduced coverage area, or a low-weight mounting strategy. A buyer should be cautious of any installer who promises a retrofit without any structural review: the cost of a proper assessment is minor compared with the cost of fixing a failed roof, and responsible steel structure suppliers will ask for or provide this review as part of the project.

Roof System Types and Matching Mounting Methods

Not all steel roofs are the same, and the mounting method must match the actual roof profile. The most common combinations in industrial steel construction are the following.

Standing Seam Metal Roofs: Clamp-On Mounting

Standing seam roofs, with raised seams running up the slope, are widely regarded as the most solar-friendly profile because specialized clamps grip the seam without piercing the sheet. No penetration means no new leak paths, fast installation, and the roof membrane or coating warranty is generally preserved. The main engineering checks are the clamp's pull-out and shear capacity relative to the seam profile, and the seam's ability to resist the applied loads over the building's design wind conditions. For buyers planning a new factory or warehouse with a serious solar intention, requesting a standing seam roof profile is a sensible default.

Trapezoidal and Corrugated Steel Roofs: Bracket Mounting

Trapezoidal and corrugated profiles, common on workshops and warehouses, usually use aluminum or stainless steel brackets that sit in the troughs of the sheet and fix into the purlin beneath, sealed with EPDM gaskets and appropriate sealant. The critical points are fixing into the purlin rather than only into the sheet, correct bracket positioning in the flat of the trough, and workmanship of the sealing. Done correctly with quality components, these penetrations remain watertight for the life of the installation; done carelessly, they are the most common source of retrofit leaks.

Fastened Roofs with Rails: Distributed Load Design

Whether clamped or bracketed, most metal roof solar installations mount rails parallel to the purlins or perpendicular across them, with modules fixed to the rails. Rail spacing distributes the module load into many attachment points, which keeps the load per fixing low. The number and spacing of attachments is set by wind and snow calculations for the specific site, not by rule of thumb, and the system supplier should provide these calculations as part of the deliverables.

Flat or Low-Slope Steel Decks: Tilted Frames and Ballast

Some industrial buildings use shallow-slope roof decks with insulation and membrane. On these, photovoltaic arrays are often mounted on tilted aluminum frames to reach a productive angle. Where penetrations are undesirable, ballasted systems are used, but buyers should remember the trade-off described earlier: ballast replaces penetration with weight, and the structural check then focuses on the deck's capacity for the heavier distributed load and on drainage around the ballast rows. On lightweight steel decks this option needs particularly careful verification.

Regional Design Considerations for International Projects

Because steel structure buildings are traded across borders, buyers and suppliers usually work across very different climates. The same building type asks different questions of its solar-ready roof in each region, and procurement teams serving multiple markets benefit from understanding these differences before fixing a specification.

In tropical and coastal markets, high humidity, salt-laden air, and intense UV exposure raise the importance of coating systems and material compatibility. Fasteners, clamps, and brackets should be specified with corrosion protection matched to the environment, and inspection intervals should be shortened accordingly. The wind case, including typhoon exposure where relevant, usually governs the array anchorage, so site-specific wind calculations deserve more weight than in calmer inland regions.

In cold and snowy regions, the combination of photovoltaic loads with heavy snow accumulation and drifting behind panel rows becomes the governing check. Row spacing, array height above the roof surface, and the strength of the lower edge fixings all interact with snow behavior. Buyers in these markets should ask explicitly how the snow case has been combined with the array loads, because treating them separately can seriously understate the real demand on the purlins.

In hot, arid regions with high dust levels, the main questions are less structural and more operational: dust accumulation reduces energy yield and increases cleaning frequency, and extreme roof temperatures affect cable and connector selection. Nonetheless, thermal movement of long steel runs and expansion joints for rails still belong in the structural conversation, because fixings that are rigid against a moving roof will eventually work loose.

In seismically active markets, anchored rooftop equipment is subject to restraint rules in many codes, and mounting systems or restraint details certified for seismic conditions should be specified from the outset. A buyer importing a generic mounting kit into such a market should verify that it complies with the local seismic provisions rather than assuming international equivalence.

Waterproofing and Corrosion Protection

Water is the most common practical failure mode of rooftop solar retrofits, and corrosion is the most common long-term risk. Both are manageable with the right details and materials.

For penetrating mounts, every fixing should use sealed, stainless or properly coated hardware with EPDM washers, and the sealant system should be compatible with the roof coating. The workmanship of a penetration matters more than the component itself: a correctly seated bracket with a compressed gasket will outlast a generously silicone-sealed guess. For clamp-based standing seam systems, the absence of penetration removes most leak risk but shifts attention to galvanic compatibility between aluminum clamps, coated steel seams, and stainless fasteners.

Galvanic corrosion is a genuine consideration when dissimilar metals meet in a wet environment. Quality mounting systems isolate aluminum from steel where needed and use stainless fixings throughout. Buyers reviewing proposals should ask what material combinations are used at every contact point, because this detail separates durable installations from ones that develop rust streaks and seized fixings within a few years.

The roof's own condition also matters. A roof with active corrosion at fasteners or laps should be renovated before a solar array is added, because once panels cover the sheet, inspection and recoating access becomes restricted. Planning the sequence — roof first, solar second — protects both investments.

Wind, Snow, and Seismic Considerations

Environmental loads deserve explicit attention in the buyer's specification, because they vary enormously between markets.

In typhoon-prone coastal regions, design wind speed and exposure dominate the anchorage design. Tilted arrays should be evaluated for uplift at edges and corners, where wind pressures are highest, and it is common to strengthen or increase fixing density in these perimeter zones. Buyers in such regions should expect the system supplier to provide wind calculations referencing the local code, and should be cautious about generic kits imported without site-specific verification.

In regions with significant snowfall, the array changes snow behavior on the roof: rows of modules create snow fences that can cause accumulation and drifting, and sliding snow can load the lower edge of the array. The structural check must therefore combine the photovoltaic load with the site's snow case rather than treating them separately. The building supplier's design team can incorporate this combination when informed early.

Seismic requirements apply in many of the markets where steel structures are exported, and anchored rooftop equipment is generally subject to seismic restraint rules in such codes. Mounting systems certified for seismic conditions, or engineered restraint details, should be specified where the local code requires them.

Roof Slope, Drainage, and Layout Planning

Good solar layout respects the roof as a drainage and maintenance surface. Rows should be arranged to avoid blocking gutters and valley gutters, to preserve walkways for maintenance access, and to leave clearance around roof penetrations, skylights, and ventilation equipment. Skylights in particular deserve care: covering them with modules is both a safety issue and a daylight loss, while locating rows too close can complicate their maintenance.

The roof slope itself influences the yield of the array, but on industrial roofs the practical choice is usually between flush-mounted modules following the roof pitch, or a modest tilt raised above the roof. Higher tilts catch more sun at some latitudes but increase wind load and row shading; flush systems are lighter and simpler but produce somewhat less energy. The right choice depends on latitude, roof orientation, and the project's energy model — and this optimization should be done jointly by the EPC installer and the building supplier so that the structural implications are known before the layout is frozen.

Electrical Integration and Safety

Although the structural question is the focus of this guide, buyers should also plan the electrical path early. Conduit runs from the array to inverters and switchgear need routes down the roof and through the building envelope; inverter locations need ventilation and shade; and DC and AC cabling on the roof should be UV-resistant, secured, and separated from walking paths. Fire safety practice on photovoltaic roofs includes rapid shutdown provisions where required, clear labeling, and keeping access for firefighters along designated paths.

Coordination between the steel building supplier and the solar installer avoids classic conflicts: penetrations made without notifying the roof supplier can void roof warranties; cable trays fixed to purlins without load verification add unnoticed weight; and inverter platforms hung from the roof structure must be included in the collateral load like any other equipment. A simple rule for buyers is to require that any rooftop equipment, beyond the modules themselves, is declared and included in the structural checks.

What Rooftop Solar Means for Project Budgets and Timelines

From a procurement perspective, the cost picture has three layers.

The first layer is the marginal structural cost of solar readiness in a new building. When the photovoltaic load is included in the frame and purlin design from the start, the additional steel mass is usually modest, and buyers commonly find this is a small percentage impact on the building package. The exact figure depends on span, bay spacing, roof area covered, and the site environment, so it should be requested as a specific quotation item rather than assumed.

The second layer is the photovoltaic system itself: modules, inverters, mounting, cabling, and installation labor. This is priced by the solar installer or EPC contractor, and market prices for modules have fallen enough in recent years that payback periods for industrial users with daytime consumption profiles are frequently attractive. The buyer's own electricity tariff and consumption pattern matter more than generic figures: a factory running daytime shifts consumes exactly when the array produces.

The third layer is the cost of coordination and, where needed, reinforcement. For retrofits on older roofs, assessments and localized reinforcement add cost and schedule, and this is precisely the layer that early planning removes. Buyers comparing "solar-ready" new buildings against retrofits of aging roofs should include this layer in the comparison, because it is often the deciding factor.

Timeline-wise, integrating solar into a new steel building project adds little: the design inputs are handled during engineering, and the array installation follows roof completion. A retrofit, by contrast, runs its own schedule of assessment, procurement, and installation on an operating site, with the associated access and safety management. Companies planning phased expansions — a warehouse now, solar next year — should still declare the intention now: reserving the load capacity costs almost nothing and keeps every option open.

Maintaining a Solar-Equipped Steel Roof

Once the array is installed, the roof and the photovoltaic system share the same surface, and maintenance planning should treat them as one asset. Regular visual inspections should cover not only the modules but also the attachment points: signs of gasket displacement, sealant cracking, rust staining at brackets, or loosened rail connections should be corrected promptly while the fix is still small. Where the mounting system is clamped to standing seams, an occasional torque check on a sample of clamps, following the mounting supplier's instructions, is a reasonable precaution in high-wind regions.

Roof cleaning and module cleaning interact as well. Walking paths defined in the layout should be kept clear so that maintenance staff never need to step on modules or rails, and drainage paths should be checked for debris that accumulates faster around array legs and cable trays. When roof renovation eventually becomes necessary, buyers should confirm in advance that the mounting system allows partial removal and reinstallation of modules without damaging them, because this provision strongly affects the cost of the later intervention.

Finally, keeping a documented set of as-built drawings — array layout, attachment schedule, load calculations, and warranty documents — in the building's maintenance file makes every later decision easier, whether that decision involves adding capacity in a second phase, replacing modules, or selling the property. Buyers who request these documents as part of the deliverables protect the long-term value of both the roof and the energy asset.

How Steel Roofs Compare with Other Roof Types for Solar

Buyers evaluating different construction methods for a new facility often ask whether the roof type changes the solar equation. It does, and the comparison usually favors steel for industrial applications.

Concrete roofs carry heavy dead loads, which means the relative impact of a photovoltaic system is smaller in percentage terms, but drilling into structural concrete slabs is difficult, waterproofing repairs are laborious, and retrofitting anchors requires specialized equipment. On many concrete buildings, ballasted systems become the default choice simply because penetration is unattractive, and the ballast weight then consumes part of the capacity advantage that concrete enjoyed in the first place.

Timber and lightweight composite roofs fall at the opposite end: their load reserves are often limited, fixings pull out of thin decking, and insurers treat fire behavior differently. These structures frequently need verified reinforcement before any array is mounted, which adds cost and delay that a steel building usually avoids.

A steel structure building sits in the practical middle: light enough that a photovoltaic system is a small relative addition, strong and regular enough that load paths are easy to calculate, and compatible with both penetrating brackets and non-penetrating clamps depending on the roof profile. Purlin spacing provides a natural grid for attachment, and factory-engineered members make reinforcement, where needed, a bolted and predictable exercise rather than an improvised one. For buyers whose energy strategy includes rooftop generation, this combination of lightness, regularity, and calculability is the core structural argument for steel.

A Procurement Checklist for B2B Buyers

Buyers evaluating steel structure building offers with rooftop solar in mind can use the following checklist to compare suppliers and protect the project.

• Declare the solar intention at RFQ stage, including target coverage area, mounting technology if known, and whether the system is phase one or a future phase.
• Ask the supplier to include the photovoltaic collateral load in the frame and purlin design, and to state the reserve capacity available on the as-designed roof.
• Request the roof profile recommendation for the intended mounting method, for example standing seam for clamp systems, and confirm the profile supports non-penetrative fixing if that is preferred.
• Require site-specific wind and, where relevant, snow and seismic calculations for the mounting system, referencing the local code, not generic certificates.
• Confirm material compatibility at every contact point: clamp-to-seam, bracket-to-sheet, fastener materials, and isolation between dissimilar metals.
• Clarify warranty interaction: how the roof warranty treats solar penetrations or clamps, and who is responsible for leak-free workmanship at attachments.
• For existing buildings, commission a structural assessment before signing the solar contract, covering purlin capacity, roof condition, and fixing feasibility.
• Agree the layout rules: walkways, skylight clearances, gutter zones, and maintenance access are preserved in the array design.
• Plan the electrical route early: inverter locations, conduit penetrations through the envelope, and any rooftop equipment platforms declared to the structural engineer.
• Sequence the works: roof renovation before solar on older roofs, and array installation scheduled after roof completion on new builds.
• Require as-built documentation: array layout, attachment schedule, structural calculations, and warranty papers delivered with the project handover.

A supplier who answers these points with specific, project-based engineering — rather than generic assurances — is demonstrating exactly the capability that a rooftop solar project needs. The questions themselves are a useful filter during supplier selection.

Common Mistakes Buyers Should Avoid

Field experience across many industrial solar projects points to a handful of recurring mistakes, all of which are avoidable with planning.

The first is treating solar as a late addition. When the array is an afterthought, every structural question becomes a retrofit question, roof warranties become contested, and the cheap option of designing capacity in has already been lost.

The second is selecting mounting hardware purely on price. The mounting system is a small fraction of project cost but carries the entire array through decades of wind and weather. Underspecified clamps and brackets are the components most likely to fail, and their failure mode — modules working loose on a roof — is among the most expensive to remedy.

The third is ignoring the roof's own life stage. Installing a twenty-five-year energy asset on a roof with five years of coating life left guarantees a later removal-and-reinstall project, which is far more expensive than renovating the roof first.

The fourth is accepting averaged load numbers without point checks. A whole-roof average that looks comfortable can still overload individual purlins or fixings where rails concentrate load. The structural review should confirm load paths, not just totals.

The fifth is overlooking drainage and access in the layout. Arrays that block water paths or eliminate walkways create operational problems that have nothing to do with electricity, and fixing them later means disturbing the installation.

Frequently Asked Questions

Can every existing steel structure building take solar panels without reinforcement?

No. Many can, especially lighter photovoltaic systems on reasonably modern roofs in moderate climates, but the answer depends on the original design reserve, roof condition, and the local wind and snow environment. A structural assessment is the responsible way to know, and it is inexpensive relative to the project.

How much load does a typical rooftop photovoltaic system add?

As a planning reference, common flush or tilted systems on metal roofs add roughly 12 to 17 kilograms per square meter of covered roof area including mounting hardware, while ballasted systems can be significantly heavier. Final figures must come from the system supplier's calculations and the project engineer's verification for the specific site.

Will mounting solar panels cause my steel roof to leak?

Not if the workmanship and components are right. Clamp systems on standing seam roofs do not penetrate the sheet at all. Bracket systems on trapezoidal roofs penetrate, but a correctly seated bracket with a compressed EPDM gasket, fixed into the purlin, remains watertight. Leaks almost always trace back to poor sealing practice or fixing into the sheet only, both of which are preventable through specification and supervision.

Is it cheaper to design solar readiness into a new building or retrofit later?

Designing the load capacity and roof profile in from the start is almost always cheaper than a retrofit, because small steel section increases during design cost far less than assessments, reinforcement, and warranty complications later. Buyers planning solar within a few years of a new building should declare it at RFQ stage.

Which roof profile is best for solar panels?

Standing seam profiles are generally the most solar-friendly because non-penetrating clamps are available. Trapezoidal and corrugated profiles work well with properly sealed brackets. Flat or low-slope decks can use tilted frames, but ballasted options need careful structural verification on lightweight steel decks.

Does a solar array affect the building's fire safety or insurance?

Both deserve attention. Modern photovoltaic practice includes rapid shutdown, labeling, and access paths for firefighters, and buyers should confirm these provisions with their installer. Insurers increasingly ask about rooftop photovoltaic systems; declaring the design details — mounting method, electrical protection, and structural verification — usually makes the conversation straightforward.

Can we install solar on only part of the roof?

Yes, and partial coverage is common, particularly where skylights, vents, or budget limits the area. Partial arrays still need the same structural and waterproofing care, and leaving capacity reserved for future phases is a sensible strategy for growing companies.

How long does a rooftop photovoltaic system last compared with the roof itself?

Modules are commonly warranted for 25 years or more, while coating systems on steel roofs have shorter service intervals depending on the environment. This mismatch is exactly why the roof's remaining life should be checked before installation: aligning the roof's condition with the array's expected service period avoids the cost of removing and reinstalling the system for roof work later.

Does adding solar panels change how the building handles lightning?

A metallic array on a roof should be included in the building's lightning protection assessment. Depending on the local code and the existing protection system, the array may need bonding into the lightning protection network, and surge protection on the DC and AC sides should be specified. These points belong in the early coordination between the installer and the building's electrical designer.

What should we ask a steel structure supplier about solar readiness?

Ask whether the offered frame and purlin design includes photovoltaic collateral load, which roof profile they recommend for the intended mounting system, what reserve capacity remains, how wind uplift at the array is handled, and how the roof warranty treats the mounting method. Specific answers to these questions separate solar-ready offers from generic ones.

Conclusion: Plan the Roof and the Power Together

So, can a steel structure building roof carry solar panels? In the great majority of well-engineered cases, yes — and the steel building is often the easiest platform for rooftop photovoltaics precisely because its structure is light, regular, and calculable. But the confident answer comes from engineering, not optimism: the additional loads, the wind and snow environment, the roof profile, the mounting method, and the roof's condition all need to be checked and matched.

For B2B buyers, the practical takeaway is simple. Treat the rooftop as a planned asset. Declare the solar intention early, request the structural verifications as part of the building quotation, choose roof profiles and mounting systems that suit each other, and sequence roof and solar works sensibly. Companies that follow this path obtain a building whose largest unused surface becomes an income-generating, cost-reducing asset — without surprises, without leak disputes, and without paying twice for the same roof.

If you are planning a steel structure warehouse, workshop, or industrial facility and want the roof engineered for photovoltaics from the start, share your building dimensions, location, and solar intentions with our engineering team. We will return a design proposal in which the structure and the energy plan are verified together — the way a rooftop asset should be built.