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Designing a roof safely and economically starts with two facts: the locally adopted building code sets mandatory minimums, while an insurer may impose additional property-protection criteria. The eight rules below, adapted from the 2010 Building Design + Construction article, remain a useful decision sequence—but the article’s code comparisons and FM references are historical. For a current project, establish the jurisdiction, adopted code edition, structural loads, insurer requirements and complete roof assembly before writing a specification.
That sequence prevents two expensive errors: omitting a requirement that affects coverage or approval, and copying an FM designation into a generic specification when the project does not need it. Current FM guidance is specific to its scope and approval process, and the 2024 International Residential Code (IRC) Chapter 9 is only applicable where that code has been adopted, as amended, by the authority having jurisdiction.
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Begin with a project brief, not a product name. Record the site, occupancy or risk category, building geometry, roof areas and slopes, existing-roof condition, climate and snow or rain data, rooftop equipment, photovoltaic or vegetated-roof plans, energy targets, fire objectives, and the authority’s adopted code. Then identify the insurer and ask for its current, project-specific criteria.
No source supplied for this article can determine your project’s required wind pressure, snow load, drainage capacity, fire classification, energy performance, attachment design or FM rating. Those values require the applicable code, engineered calculations and manufacturer instructions. A roof that is acceptable in one jurisdiction or for one insurer can be unsuitable in another.
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1. Is the building insured by FM, or does another insurer require FM criteria?
Find this out before selecting roof criteria. Ask the owner, broker and insurer whether the property is insured by FM, whether a lender or loss-control program references FM, and which edition of each applicable data sheet governs the work.
The original 2010 article reported that FM insured “about 15-20% of the nation’s building stock.” That was an estimate presented at the time, not a current market statistic, and it had no underlying study or reference year in the article. Do not use it to assume that FM requirements apply to a new project.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsCurrent FM Data Sheet 1-28 addresses wind considerations for property protection at highly protected buildings. Its scope includes building components and cladding, opening protection and specified roof-mounted equipment, while directing designers to the ASCE 7 edition required by the local code for the main wind-force-resisting system and other structures. The search record identifies an interim revision in April 2026, so obtain the current document rather than relying on an old PDF.
2. Why should you avoid putting FM language in every roof specification?
Do not add an FM rating simply because it appears in a familiar office master specification. First establish that the owner’s insurer, contract or risk-management program requires it. Otherwise, a boilerplate requirement can narrow the available assemblies, add coordination and documentation work, or increase cost without solving a project requirement.
The 2010 article quoted roofing-industry veteran Joseph Schwetz: “The roofing industry, including manufacturers, is guilty of creating generic, boilerplate specifications that state a building shall meet FM 1-90 UL Class A.” The warning is about careless specification, not about avoiding robust design. If a project needs FM approval, state the exact approved assembly, rating and installation conditions. If it does not, specify the code-required performance and any owner objectives directly.
Keep code and insurer criteria in separate, traceable sections of the basis of design. A code provision is enforceable through the authority having jurisdiction; an insurer’s condition may be contractual or tied to coverage. Both can matter, but they are not interchangeable.
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3. How do you use RoofNav to select an FM roof assembly?
Use RoofNav to find a complete FM Approved assembly that matches the project’s construction and performance needs. RoofNav is a selection resource, not a substitute for design calculations or the manufacturer’s installation instructions.
- Define the inputs. Confirm deck type, insulation arrangement, membrane or covering, attachment method, roof slope, perimeter and corner conditions, and the required wind, hail and exterior-fire performance.
- Enter the project conditions. Use the wind pressures or ratings developed from the applicable code and insurer criteria. Include roof-mounted equipment and openings where the data sheet requires them.
- Filter for a complete assembly. Select an FM Approved roof system whose listed components and attachment pattern correspond to the proposed construction. Record the approval number and limitations.
- Check the rating ceiling. FM Data Sheet 1-29 says not to exceed the assembly’s FM approval rating. A higher design demand requires a different approved assembly or a revised design; it is not solved by describing the chosen assembly as “equivalent.”
- Coordinate installation. Make the drawings, specification, shop drawings and manufacturer details agree with the approved configuration, including fastener spacing, edge zones, penetrations, seams, insulation and cover boards.
The FM Data Sheet 1-29 is explicit that individual FM Approved materials do not create an FM Approved assembly when they have not been approved for use together. A membrane, adhesive, insulation board and fastener can each carry an approval and still be an unapproved combination.
4. What is the difference between an approved product and an approved assembly?
An approved product has been evaluated for the uses listed in its approval. An approved assembly has been evaluated as a coordinated roof build-up, including the deck, insulation, cover board, membrane or covering, fasteners or adhesive, joints and relevant details. Wind uplift, hail and fire performance depend on those interactions.
Require the contractor and manufacturer to identify the exact assembly, not merely a family of products. Review substitutions against the approval listing before they are accepted. A seemingly minor change—different fastener diameter, insulation thickness, cover-board orientation, adhesive, spacing or perimeter detail—can move the work outside the approved configuration.
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This principle also applies when a code evaluation and an insurer approval are both required. Document which evidence satisfies the code and which evidence satisfies the insurer; neither document automatically replaces the other.
5. Are FM requirements always stricter than building code?
No universal ranking is safe. The 2010 article characterized FM specifications as stricter than code, but that was the author’s description in that edition and context. Current FM guidance is scoped to property protection, while the adopted building code covers legal minimum requirements for the building and its occupants. A requirement can be more demanding in one performance area and not address another.
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Use a matrix with one row for each design issue:
| Design issue | Code source | Insurer or FM source | Design record |
|---|---|---|---|
| Wind pressures and resistance | Locally adopted code and its referenced ASCE 7 edition | FM 1-28 and the applicable FM assembly rating | Signed calculations, zones and attachment schedule |
| Roof covering and fire classification | Adopted code provisions and listed assembly | FM 1-29 assembly and exterior-fire rating, if required | Listing, test or approval documents |
| Drainage and slope | Adopted code, plumbing provisions and engineered drainage | FM criteria within their scope | Plan slopes, drains, overflows and flow paths |
| Rooftop equipment and openings | Structural, fire and energy provisions | FM 1-28 property-protection provisions where applicable | Curbs, screens, penetrations and attachment details |
Resolve conflicts with the authority having jurisdiction, the structural or roofing designer and the insurer. Never assume that a generic statement such as “meet FM 1-90 and UL Class A” identifies one valid, buildable assembly.
6. How do FM revisions affect a roof specification?
Check the current FM data sheets at the start of design, at specification issue and when submittals are reviewed. FM criteria and approval listings can change; the available data identifies an April 2026 interim revision to Data Sheet 1-28. Record the revision date and the approval information used for the project.
When FM insures the building, involve its engineering or loss-prevention personnel early enough to resolve unusual conditions. Early review is especially important for large rooftop units, high parapets, complex perimeters, combustible construction, unusual decks, photovoltaic arrays and vegetated roofs.
Make the contract documents identify who verifies that a proposed substitution remains within the current approval. A substitution accepted only by the architect or contractor may still be unacceptable to the insurer. Ask for written confirmation where the insurer’s conditions require it.
7. What review and inspection should you expect on an FM-insured project?
The 2010 article describes review and follow-up inspection as part of FM’s approval process. Treat those activities as project milestones, not paperwork to complete after installation.
- Submit the design basis, calculations, RoofNav assembly reference and details before procurement when the insurer requires preconstruction review.
- Hold a preinstallation meeting with the roofing contractor, manufacturer’s representative, designer and insurer’s representative where applicable.
- Verify deck condition, fastener type and spacing, substrate dryness, insulation layout, perimeter zones, penetrations and temporary protection as work proceeds.
- Keep delivery tickets, photographs, daily reports, test records, approved submittals and change documentation.
- Close punch-list items and preserve the as-built assembly record for future repairs, reroofing and insurance audits.
Inspection does not transfer design responsibility to the inspector. The design professional remains responsible for the design, the contractor for means and methods and installation, and the manufacturer for its instructions and warranty conditions.
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8. What changes when the roof is vegetated or carries equipment?
A vegetated roof adds permanent and temporary load, moisture and maintenance conditions. Calculate saturated media, plants, drainage layers, retained water, snow and construction loads; then verify the deck, structure, waterproofing, root resistance, fire performance and edge restraint. Coordinate wind-uplift resistance for the growing medium and all layers with the insurer and the assembly manufacturer.
Solar arrays, mechanical units, screens, walkways and fall-protection systems also add weight and wind area. Show their curbs, rails, sleepers, penetrations and attachment forces on structural and roofing details. Do not attach equipment through a membrane or insulation layer without a detail that preserves waterproofing and remains within the assembly approval.
Drainage deserves a separate review. FM Data Sheet 1-29 gives a minimum slope recommendation of 1.2 degrees (1/4:12) within its guidance to facilitate drainage. That value is not a universal substitute for the locally adopted code or the project’s engineered drainage design. Confirm positive drainage, primary drains, overflow routes, scuppers, tapered insulation, cricketing and maintenance access.
What does current code cover for roof assemblies?
Where adopted, the 2024 IRC Chapter 9 addresses roof-assembly design, materials, construction and quality. Its scope includes wind resistance, drainage, flashing, insulation, rooftop photovoltaic systems, and roof-covering recovery and replacement. The exact enforceable text depends on the jurisdiction’s adopted edition and amendments; commercial buildings may instead be governed by the adopted International Building Code or another local code.
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Use the code’s referenced standards and local amendments to establish minimum performance, then add insurer criteria only where they apply. For every roof area, document fire classification, thermal performance, wind resistance, drainage, flashing, penetrations and replacement limits. Existing roofs require a condition survey and verification that the proposed recovery or replacement method is permitted.
What is a practical design workflow for a roof project?
- Confirm jurisdiction and occupancy. Identify the authority having jurisdiction, adopted code editions and amendments, occupancy or risk category and permit path.
- Confirm insurance criteria. Obtain the insurer’s written requirements, FM involvement and current data-sheet editions.
- Develop loads. Have the design team establish wind, snow, rain, seismic where applicable, equipment, photovoltaic and vegetated-roof loads.
- Set performance targets. Define slope, drainage, fire, hail, energy, service life, maintenance and replacement objectives.
- Select the assembly. Use RoofNav for an FM project and verify a complete assembly’s rating, limitations and installation conditions.
- Coordinate details. Resolve edges, corners, curbs, drains, penetrations, expansion joints, parapets, walkways and temporary conditions.
- Review substitutions and inspections. Require documented equivalency or insurer acceptance before changing an approved component or configuration.
- Archive the record. Keep the final drawings, calculations, approval listings, submittals, inspection reports and maintenance requirements.
What are the most common specification failures?
| Failure | Why it causes trouble | Prevention |
|---|---|---|
| Copying an FM rating into a master spec | It may overdesign the roof or conflict with available assemblies. | Verify the insurer, exact rating and project need first. |
| Combining separately approved products | The combination may not be an approved assembly. | Specify and install one listed assembly, including details. |
| Using an outdated data sheet | Criteria, ratings or scope may have changed. | Record current revision dates at design and submittal review. |
| Treating code and FM as interchangeable | They serve different legal and property-protection purposes. | Map each requirement to its source and responsible reviewer. |
| Ignoring saturated vegetated-roof weight | Structure, fasteners and uplift resistance can be inadequate. | Design for all permanent, temporary, water and snow loads. |
| Leaving drainage to the installer | Low spots and blocked flow paths can cause ponding and leaks. | Show slopes, drains, overflows and maintenance access in design. |
How should an owner or designer read the 2010 recommendations today?
Read them as a decision sequence: identify the insurer, avoid unjustified boilerplate, consult RoofNav when FM applies, select a complete approved assembly, distinguish insurer criteria from code, monitor revisions, plan review and inspection, and design vegetated roofs for load and uplift. The sequence remains practical, but every technical value must be refreshed against the current code, insurer documents and manufacturer instructions.
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As Schwetz put it, “It’s important for those involved in roof design to know the difference between FM [requirements] and building code.” That distinction is the key to a roof that is legally compliant, insurable, buildable and appropriate for the owner’s actual risk.
Frequently Asked Questions
Can a roof meet the building code without having an FM approval?
Yes, if the locally adopted code and the project contract do not require FM approval. An insurer, lender or owner risk program can impose additional conditions, so confirm those obligations before assuming code compliance is sufficient.
Does every component in an FM roof need its own FM approval?
The critical requirement is a complete FM Approved assembly whose listed components are approved for use together. A component’s individual approval does not make an unlisted combination an approved assembly.
What slope should a low-slope roof have for FM work?
FM Data Sheet 1-29 gives 1.2 degrees, or 1/4:12, as a minimum slope recommendation within its guidance to aid drainage. The project still must satisfy the adopted code, engineered drainage design and the selected assembly’s limitations.
Who approves a roof substitution on an FM-insured building?
The design team should verify the substitution against the current assembly listing and manufacturer instructions, and the insurer should review it when its requirements call for approval. Keep written acceptance and the final assembly documentation with the project record.
