Joisted Masonry Construction
Published: November 4, 2026 · Last reviewed: November 4, 2026 · Est. reading time 5 minutes
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In plain language: Joisted masonry construction describes a building with brick, block, or stone outer walls but wood floors and a wood roof. Insurers use the label to price fire risk on commercial buildings.
Technical definition: Joisted masonry construction is ISO Construction Code 2 in the Commercial Lines Manual. The class covers buildings with exterior walls of masonry material, such as brick, concrete block, gypsum block, stone, or tile, and a combustible floor and roof.
Joisted Masonry Construction at a Glance
| Attribute | Detail |
|---|---|
| Also known as | JM, ISO Code 2 |
| Category | Building classification for property rating |
| Lines of business | Commercial property, businessowners policy |
| Industries most affected | Retail stores, strip malls, office buildings, light industrial facilities |
| Common solution | Accurate construction type on the application |
| Also interacts with | Occupancy, fire protection, sprinkler systems |
Key Takeaways
- ISO ranks six construction types, and Code 2 means masonry outer walls with a combustible floor and roof.
- Construction class drives property insurance pricing, so a wrong class changes the client's insurance premiums.
- Agents often mistake brick veneer over wood studs for masonry, but ISO rates veneer buildings as frame.
- CSRs should confirm wall, floor, and roof materials before picking a class.
What Is Joisted Masonry Construction in Insurance?
Joisted masonry construction is one of six building construction categories the Insurance Services Office (ISO) uses to rate commercial property. These construction classifications rank how easily a building burns, from construction class 1 (frame) to Code 6 (fire-resistive).
Masonry holds up well in a fire, but wood joists and a combustible roof assembly can still feed flames inside. That mix places Code 2 one step above frame. Hollow concrete block, lightweight concrete blocks, reinforced masonry, and other masonry materials all count for the walls.
A one-story shop with concrete masonry units for walls and engineered wood trusses holding the roof is a typical joisted masonry building, rated as construction class 2. Mill construction, also called heavy timber construction, is a sturdy, slow-burning form of the same class.
How Does Joisted Masonry Construction Work?
- Building inspection. An agent or inspector records walls, floors, and roof from site visits or commercial property reports.
- Class selection. Masonry walls plus a wood floor and roof point to Code 2.
- Rating. Insurers apply ISO loss costs for the construction type, occupancy, and protection class.
- Underwriting decisions. Carriers weigh sprinklers, roof condition, building codes, and overall risk assessment before offering terms.
Claim Examples Involving Joisted Masonry Construction
Strip mall roof fire spreads across tenant spaces.
A strip mall had block walls and a wood truss roof. A kitchen fire spread through the roof into three tenant spaces. The walls stayed standing. Because the class on the application was correct, the carrier paid without a misrepresentation dispute.
Veneer office misclassified as masonry.
An agent listed a small office as Code 2 because of its brick front. After a fire, the adjuster found brick over wood studs, which ISO treats as frame. The carrier questioned the application, and the agency faced an E&O claim.
Joisted Masonry Construction vs. Frame Construction: What Is the Difference?
Joisted masonry vs. frame construction comes down to the outer walls. Code 2 uses load-bearing masonry, while frame uses wood walls, including wood covered by brick or stone veneer. Both classes have combustible floors and roofs.
| Comparison area | JM (Code 2) | Frame |
|---|---|---|
| Primary use case | Masonry-walled commercial construction | Wood-walled buildings and habitational dwellings |
| ISO code | 2 | 1 |
| Outer walls | Brick, block, stone, tile | Wood, veneer, stucco over wood |
| Fire resistance | Higher than frame | Lowest of six classes |
| Common mistakes | Coding a metal-roof building as Code 2 | Coding veneer as masonry |
What Are the Most Common Mistakes With Joisted Masonry Construction?
- Calling veneer masonry. Veneer over wood is frame, so the policy is underpriced and coverage disputes follow.
- Missing a noncombustible roof. Block walls with a metal frame roof and metal deck can qualify for Code 4, so the client overpays.
- Ignoring the fire resistance rating. Buildings with rated walls, floors, and roof may fit modified fire-resistive construction or Code 6 instead.
- Skipping documentation. A missing photo or inspection note leaves the agency with no proof of the class it chose, weakening fire safety records and any E&O defense.
Sources and References
- International Risk Management Institute (IRMI). Joisted Masonry Construction.
- International Risk Management Institute (IRMI). Building Construction Categories (ISO).
- International Risk Management Institute (IRMI). Frame Construction (ISO).
- International Risk Management Institute (IRMI). Mill Construction.