Picture a hypothetical job. The PV layout is finished on a 2D roof plan. Then the model shows the rooftop unit (RTU) service side under two rows of modules. A hatch has no pathway to the parapet. A drain sump sits below a rack. None of these are modeling errors. Each one is a rule that nobody loaded into the federated model before the PV layout was released.
Solar BIM coordination fixes that sequence. This guide is for MEP subcontractors and design coordinators on a US BIM job. On that job a rooftop PV array shares the roof with mechanical, plumbing, fire and electrical work. It shows how to zone the roof, load the clearance rules, route conduit to the electrical room and test it all in one model. The BIM services hub covers the wider modeling and coordination support.
Quick answer. Solar BIM coordination puts the rooftop PV layout in the same federated model as RTUs, vents, drains, hatches and conduit routes. It then tests the layout against written clearance rules, not only geometry. Zone the roof first. Load clearance volumes from manufacturer drawings and the adopted IFC, IMC and NEC editions. Give every clash one owner who moves, then retest before the PV layout is released.
Sources were checked on 31 October 2026. Code text was read through UpCodes and AHJ or manufacturer documents, because the model codes are login-gated at the publisher. Local amendments and the project documents control. Where this guide describes practice rather than a source, it says so.
Why does solar BIM coordination need its own pass on a roof?
Rooftop PV claims roof area that other systems already need. The fire code measures its pathways from those same objects, so the PV layout cannot be settled until the equipment is placed.
The International Fire Code (IFC) says so directly. The IFC 2021 as adopted by Houston shows the rule in Section 1205.2. Pathways shall be “located in areas with minimal obstructions, such as vent pipes, conduit or mechanical equipment.” The code puts the burden on layout, and layout lives in the model.
Three habits create these conflicts:
- The PV designer works from a roof plan, not from the MEP model.
- The RTU or vent is moved late and nobody reruns the pathway check.
- The PV contractor is engaged after the building design is set. The authors of an IIBEC article on commercial roof design (January 2026) say that later engagement can cause timeline and communication gaps.
A generic clash test finds modules touching equipment. It does not find a module sitting inside a service clearance or a pathway that no longer reaches a hatch. Those are rule violations, so the model needs rules. The BIM clash detection workflow guide covers the general method. This guide adds the roof-specific rules.
This guide assumes an actual PV design. Roof allowances for a future array are a different job, covered in the solar-ready building design guide.
How do you zone the roof before placing any modules?
Zone the roof by what must stay clear, then place PV in what is left. Every zone is a model object with a named source, so the test can run without anyone re-reading a code book.
| Zone | What it holds | Where its dimension comes from | Model object |
|---|---|---|---|
| Perimeter | Fire perimeter, guards, edge access | IFC 1205.3.1 and the guard rules cited by the project | Offset band from the roof edge |
| Access | Hatches, stair bulkheads, ladders | IFC 1205.3.2; IMC 2021 Section 306.5 | Footprint plus pathway band |
| Equipment | RTUs, exhaust fans, condensers | Manufacturer drawing; IMC 2021 Section 306.1 | Envelope plus service volume |
| Penetrations and vents | Plumbing vents, flues, smoke vents | IFC 1205.2 and 1205.3.3; vent manufacturer | Keep-out volume |
| Drainage | Drains, sumps, scuppers, overflows | Project rule set at the BIM plan | Keep-out plus maintenance zone |
| Structure | Framing lines, curbs, load limits | Structural engineer of record | Load zone with capacity note |
| PV field | Modules, racking, ballast, DC conduit | Remainder after the zones above | Array block at tilt and height |
The order matters. The PV field is the last object placed, not the first.
Illustrative roof budget
This example is illustrative. It uses assumed numbers to show the method, not a real project. Take a flat commercial roof of 180 ft by 120 ft with four RTUs and two roof hatches.
| Step | Assumption | Area (sq ft) | Remaining (sq ft) |
|---|---|---|---|
| Gross roof | 180 ft x 120 ft | 21,600 | 21,600 |
| Fire perimeter | 4 ft band, allowed because both axes are 250 ft or less | 2,336 | 19,264 |
| Interior pathway | One 8 ft pathway across the 180 ft axis (the 150 ft interval rule), using the smoke ventilation option | 896 | 18,368 |
| RTU zones | Four reserved zones of 14 ft x 20 ft, each covering the unit plus an assumed service volume | 1,120 | 17,248 |
| Hatch zones | Two zones of 11 ft x 11 ft (an assumed 3 ft hatch plus a 4 ft pathway on every side) | 242 | 17,006 |
The PV field has about 17,000 sq ft, or 79 percent of the gross roof. The zones are added without overlap here, so the true figure is slightly higher, but drains, vents and shade from equipment would lower it again. The point is the sequence: each subtraction has a source, and each one moves when equipment moves.
What clearances apply around rooftop equipment?
Use the largest of three values on each side of the equipment: the manufacturer’s clearance, the mechanical code’s working space, and any local amendment. Record the source on the clearance object so the model shows why the number is there.
Manufacturer. Start with the installation instructions for the exact unit. The Carrier 50FC-*16 installation instructions (Form 50FC-16-01SI Rev. A, February 2022) give one example. Figure 3 lists service clearances from a 12 in. minimum, with 18 in. recommended, up to 48 in. where a unit disconnect is mounted on the panel. It lists 36 or 42 in. where the person servicing stands facing a nonconductive or grounded surface. It also says the unit “is not designed to have overhead obstruction” and sends the designer to the manufacturer for any overhead condition. Other models differ, so read the drawing for the unit on the project.
Mechanical code. IMC 2021 Section 306.1 requires a level working space at least 30 in. deep and 30 in. wide in front of the control side of an appliance. IMC 2021 Section 306.5 covers access to equipment on roofs. If personnel must climb higher than 16 ft above grade, access cannot require portable ladders or climbing over obstructions taller than 30 in. We read both sections in the IMC 2021 as adopted by Seattle, which marks Section 306.5 as locally amended. Confirm the base text and your own AHJ’s version.
Local amendment. Some states add their own number. The Oregon Fire Code 2025, which amends IFC 2024, requires a clearance of not less than 30 in. around mechanical equipment requiring service or maintenance (Section 1205.3.4.2). Roofing guidance quoted in the IIBEC article cites the National Roofing Contractors Association (NRCA) for at least 30 in. from walls, curbs or adjacent racks.
Two more details for the model:
- Service volume, not footprint. Model the clearance as a 3D box. The clash test then sees a module in front of a panel door.
- Heat and intake. The Carrier instructions say to check for flue products within 10 ft of the fresh air intake hood. Treat any PV equipment that blocks airflow as a mechanical question, not only a PV one.
Electrical equipment on the roof, such as inverters and disconnects, has its own working space under NEC Section 110.26 (Spaces About Electrical Equipment). The inverter’s installation guide adds model-specific clearances. Pull both for the edition the AHJ adopted.
Which fire access rules shape the layout?
For buildings other than Group R-3, IFC Section 1205.3 sets the perimeter, interior pathways and smoke ventilation. The dimensions are the same in IFC 2021 and IFC 2024 as published on UpCodes. The pathway and setback dimensions in Sections 1205.2 to 1205.3.3 match. The only wording changes we found concern building-integrated PV, plus spelling. We compared the IFC 2021 text with the IFC 2024 as adopted by Colorado, which UpCodes lists as adopted without amendments.
| Rule | Dimension | IFC section |
|---|---|---|
| Clear perimeter at roof edges | 6 ft; 4 ft where either building axis is 250 ft or less | 1205.3.1 |
| Interior pathways between array sections | At intervals not greater than 150 ft across length and width | 1205.3.2 |
| Pathway to roof standpipes or ventilation hatches | 4 ft wide, straight line | 1205.3.2 |
| Pathway around roof access hatches | 4 ft wide, with at least one leading to a parapet or roof edge | 1205.3.2 |
| Nongravity smoke and heat vents | 4 ft pathway on all sides | 1205.3.3 |
| Gravity dropout smoke and heat vents | 4 ft pathway on at least one side | 1205.3.3 |
| Smoke ventilation between array sections | 8 ft pathway, or 4 ft pathway bordering 4 ft x 8 ft cutouts every 20 ft on alternating sides | 1205.3.3 |
Three points change how you model this:
- Exceptions belong to the fire official. Section 1205.2 lets the fire code official waive roof access, pathways and spacing where rooftop operations will not be employed. Section 1205.3 also lets the official treat a roof as similar to Group R-3. Confirm any waiver in writing before the model drops a pathway. Do not assume it.
- One- and two-family dwellings follow the residential code. IRC 2021 Section R324.6 asks for two 36 in. pathways on separate roof planes, plus ridge setbacks of 18 in. or 36 in. depending on array coverage and sprinkler status. It does not apply to roofs of 2:12 slope or less. We read it in the IRC 2021 Section R324.6 snippet on UpCodes. For setback arithmetic on a pitched roof, see the fire setback sizing walkthrough and the fire setback glossary entry.
- Amendments move equipment, not only distances. Oregon’s amended text bars disconnects, junction boxes, combiner boxes and gutters from any required pathway or cutout. It also says raceways crossing a required pathway on a flat roof shall be bridged. That affects where the conduit and combiner objects can sit.
What structural data must the model carry?
The model does not replace the structural engineer. It carries the load points and zones so the engineer sees where the PV sits relative to framing, curbs and equipment.
The City of Portland structural requirements for solar installations list what an AHJ reviewer expects. The page does not name a code edition, so treat it as one jurisdiction’s example. It requires:
- Panel and ballast weight treated as dead load, with concentrated loads from racking supports or standoffs included.
- Roof framing checked with the array present and again without it.
- Snow drift created by the array to be considered.
- Wind loads by one of three routes: ASCE 7 Sections 29.4.3 and 29.4.4 or 30.13, wind tunnel testing, or SEAOC PV2-2017 for low-profile arrays on flat roofs.
- Seismic design per ASCE 7 Section 13.3, with unattached ballasted arrays allowed only under the conditions of Section 13.6.12 or SEAOC PV1.
Which ASCE 7 edition applies follows the building code the AHJ adopted. A Department of Defense criteria document on UpCodes cites ASCE 7-22 Chapters 29 through 31 for wind and Section 13.6.12 for seismic. For routing by state, use the ASCE 7-22 adoption guide. For rack choice and wind detail, see the flat roof racking guide and the ballasted versus penetrating mount comparison.
What to place in the model for the structural engineer:
- Equipment weights and curb locations. The Carrier unit above lists a 1,325 lb base operating weight before accessories. PV dunnage near its curb shares framing with that load.
- Framing lines and capacity notes, so each support point shows which member carries it.
- Wind zones as zones, so edge and corner areas are visible when modules are placed.
- A drift note wherever the array sits near a parapet, screen wall or unit.
For pitched roofs, the attachment detail sheet is a separate deliverable. The tile roof attachment guide covers what AHJs check there.
How should conduit reach the electrical room?
Route DC conduit as modeled objects with reserved space from the array to the electrical room, then test the route like any other system. The route has two parts, the roof run and the path through the building.
Edition and rule. Under NEC 2020 Section 690.31(D), PV dc circuits inside buildings must be in metal raceways, Type MC cable complying with 250.118(10), or metal enclosures. The rule applies above 30 V or 8 A. A course summary of that text also says that once the circuits penetrate the roof they are treated as inside the building. We read it on a continuing-education page quoting the 2020 NEC. A Mike Holt Enterprises article on the 2023 NEC (July 2024) says that edition keeps the metal raceway or Type MC requirement in 690.31(D). The same rule sat at 690.31(G) in the 2017 edition, and UpCodes shows 690.31(D) again in the 2026 edition. Read the text of the edition the AHJ enforces. The NEC edition by state guide helps find it.
Roof run. The 2020 text also requires labels reading PHOTOVOLTAIC POWER SOURCE or SOLAR PV DC CIRCUIT. They go on every wiring section separated by enclosures, walls, partitions, ceilings or floors, at spacing of 10 ft or less. In the model that means each penetration and each ceiling crossing carries a label requirement. NEC 2023 Section 690.31(F) also asks roof-mounted array wiring to allow for expected array movement. Box access matters too: UpCodes lists NEC 2023 Section 690.34 as Access to Boxes, so check that junction boxes behind modules stay reachable. The rooftop cable routing guide covers conduit fill, separation and sealing. The rapid shutdown guide covers the array boundary, which belongs in the model as its own zone.
Penetrations. The IIBEC authors advise grouping conduit penetrations into prefabricated or sheet-metal enclosures near the PV area and avoiding pitch pockets. They also advise against routing conduit through roofing insulation above the structural deck, and they cite NRCA against running it through steel deck flutes.
Path through the building. The same authors recommend reserving and labeling space in a ceiling cavity or vertical chase from the penetration to the electrical room. This is where the MEP trades matter. A conduit bank that is not modeled meets a duct or pipe riser for the first time on site. Model it with the same priority as other service routes.
Fire pathways. IFC 1205.2 asks that pathways sit where conduit is minimal. Where conduit must cross, check the local rule. Oregon, for example, prohibits raceways in required pathways on slopes steeper than 2:12.
What clash rules should the model test?
Test the PV layout against rules, each with a source, a test type and one party who moves. The matrix below is a starting set to adapt. Every value is loaded from the sources in this guide, and the project edition and AHJ replace any figure that differs.
| # | Pair tested | Test type | Value to load | Source and edition | Who moves |
|---|---|---|---|---|---|
| 1 | PV array vs RTU body and the column above it | Hard clash | Unit envelope plus vertical column | Carrier 50FC-*16 instructions: not designed for overhead obstruction | PV designer |
| 2 | PV array vs RTU service volume | Clearance | Largest of manufacturer value, 30 in. by 30 in. control-side space and any local figure | Manufacturer drawing; IMC 2021 306.1; Oregon OFC 2025 1205.3.4.2 as an example | PV designer |
| 3 | PV array vs hatch, standpipe or stair bulkhead | Clearance | 4 ft pathway around hatches with one to a parapet or edge; 4 ft straight pathway to standpipes and ventilation hatches | IFC 2021 and 2024, 1205.3.2 | PV designer |
| 4 | PV array vs smoke and heat vents | Clearance | 4 ft on all sides (nongravity); 4 ft on at least one side (gravity dropout) | IFC 1205.3.3 | PV designer |
| 5 | PV array vs roof edge | Clearance | 6 ft, or 4 ft where either axis is 250 ft or less | IFC 1205.3.1 | PV designer |
| 6 | Array section vs array section | Clearance | Pathway at 150 ft intervals; 8 ft, or 4 ft with 4 ft x 8 ft cutouts every 20 ft | IFC 1205.3.2 and 1205.3.3 | PV designer |
| 7 | PV array vs plumbing vents and exhausts | Clearance | Set from the AHJ checklist and the vent or exhaust manufacturer; no figure is loaded from this guide | IFC 1205.2 (vent pipes named as obstructions) | PV designer and MEP, decided at the BIM plan |
| 8 | PV array vs drains, sumps and scuppers | Hard clash plus maintenance volume | Project-set volume | IIBEC, January 2026: avoid arrays over drains and blocked scuppers | PV designer |
| 9 | Conduit, disconnects and combiner boxes vs required pathways | Hard clash | Pathway band; check local limits such as Oregon’s | IFC 1205.2; local amendment | Electrical designer |
| 10 | DC conduit vs ducts, pipes and shafts below the roof | Hard clash plus route reservation | Reserved route with penetration labels | NEC 2020 and 2023, 690.31(D) | Electrical designer, with MEP |
| 11 | PV support points vs framing and curbs | Structural check | Load points against framing lines | Portland PP&D guidance; IBC load provisions per adopted edition | Structural engineer of record |
| 12 | PV array vs shade from equipment, penthouses and screen walls | Soft check | Shade study result | IIBEC, January 2026 | PV designer |
Treat rows 1, 8 and 9 as hard clashes. Treat rows 2 to 7 as clearance tests against volumes. A module a few inches inside a required zone then shows up, even though no geometry intersects.
The test type matters more than the clash count. A clearance volume failing by 3 in. needs a layout decision. A hard clash on a conduit sleeve needs a model correction. Mixing the two in one list is what buries real problems.
How does the model workflow and federation run?
The workflow follows the standard coordination cycle, with one extra step before testing: load the roof rules. The general cycle is in the clash detection workflow guide.
- Set the roof scope in the BIM execution plan. Name the roof zones, the rule table above, the model authors and the PV input format. State who owns the PV layout and when it is issued.
- Agree the development level per element. A PV array for coordination needs the right footprint, tilt, height and clearance volumes more than module detail. State this by element, not as a whole-model label. BIMForum publishes a Level of Development Specification (its resources page lists the 2025 edition). The LOD 300 versus 400 guide explains how to write it.
- Fix coordinates and the roof datum. The PV layout, the architectural roof and the MEP model share one origin and level convention before the first test.
- Check the PV input on intake. The PV designer may work in a solar design tool, not a BIM authoring tool. Ask for the layout in an exchange format, plus the module, rack and conduit schedule. The phrase “solar PV in Revit” names this step in generic industry usage. Any BIM authoring tool can hold the array as simple blocks. Yield and string design stay in the solar tools. The glossary entry on solar in the MEP model gives the short version.
- Federate and test. Link architecture, structure, MEP, fire protection and PV. Load the matrix as clash tests. Run clearance tests before hard clashes, because a moved array changes both.
- Triage and assign. Each result gets one mover from the matrix and a due state. Disputed rows go to the decision owner named in the plan.
- Retest and issue. Rerun the same tests on named model versions and save the snapshot.
Cadence follows the design phase. Rerun the roof tests whenever any equipment, vent, drain or hatch moves, not only at scheduled meetings. A moved RTU can break a pathway three rows away.
Model coordination does not replace the contract documents, code review, engineering judgment or design responsibility. The discipline authors keep responsibility for their own models.
What should the coordination deliverables include?
The deliverables should let the PV contractor, the AHJ and the structural engineer each see what they need. A list that works:
- A roof coordination plan showing every zone, its dimension and its source.
- The clash-rule matrix as agreed, with edition and AHJ notes and a version date.
- A federated model snapshot tied to named model versions.
- An issue log with owner, status and closing evidence.
- A penetration and conduit schedule covering sleeves, labels and the route to the electrical room.
- A structural load-point list for the engineer of record.
- A pathway and vent diagram for fire review, drawn from the same model.
- A sign-off record that lists accepted exceptions.
Shop drawings come after this stage and have a different contract status. The MEP shop drawings guide covers that handoff. On an existing building, the roof survey step resembles the existing-condition survey in the tenant improvement MEP guide.
How can Heaven Designs help with rooftop coordination?
The BIM services hub describes federated model assembly, clash tests and issue reports across architecture, structure and MEP models. The clash detection and coordination service page lists report-only and resolution options.
If rooftop PV must sit inside that scope, say so when the scope is set. The PV layout then becomes an input with an agreed format and issue date. Turnaround is agreed at scoping.
FAQ
Can I model rooftop PV in BIM without a solar design tool?
Yes, for coordination. Block the array at the right footprint, tilt and height, add the clearance volumes and the conduit route. Yield, string sizing and shading studies still belong in dedicated solar software.
Who owns the fire pathways, the PV designer or the MEP team?
The contract and the BIM plan assign it. The fire code official decides what the AHJ requires. In practice the PV designer moves the array and the MEP team supplies accurate equipment and vent objects. Name the decision owner before the first test.
Can PV sit above an RTU?
Only if the manufacturer allows it. The Carrier 50FC-*16 instructions say the unit is not designed for overhead obstruction and refer overhead cases to the manufacturer. Treat the column above any unit as a hard keep-out until written guidance says otherwise.
Do the IFC pathway rules apply to every roof?
No. The IFC lets the fire code official waive roof access and pathways where rooftop operations will not be employed. One- and two-family dwellings follow the IRC, and local amendments such as Oregon’s change the rules. Confirm with the AHJ.
How often should the roof tests run?
Run them at every model issue and whenever equipment, vents, drains or hatches move. The roof is a shared surface, so one change can affect several rules.
Next step
Before the next PV layout is released, load the roof zones and the matrix into your federated model and run the clearance tests first. If you want help setting up that scope, start with BIM services and send the project details through the contact page.