The 2021 IBC was the first edition with special inspection requirements specific to mass timber, and Types IV-A, IV-B, and IV-C require special inspections for erection, certain connections, and anchorage. The construction documents must include a statement of special inspections, and the connections, fasteners, and fire protection being inspected must stay visible until they are approved.
What the code asks for
The WoodWorks paper Construction Quality Assurance on Mass Timber Projects: Inspection and Observation (March 2025, with PCS Structural Solutions) explains that mass timber projects are subject to many existing inspection requirements, and that the 2021 IBC was the first edition with requirements specific to mass timber. It references the 2024 IBC and says most references are identical in the 2021 edition.
For Types IV-A, IV-B, and IV-C, the paper describes IBC Table 1705.5.3, which covers anchorage and connections to timber deep foundations, erection of the mass timber, and connections whose installation method matters for the design load, such as threaded fasteners, adhesive anchors, bolted connections, and concealed connections. It also points to periodic inspection of fire-rated sealants and adhesives under Section 1705.20, and to building official inspection of wood cover that protects connections in Types IV-A, IV-B, and IV-C. Read the full paper for the details. Sources verified October 22, 2026.
Who checks what
| Activity | Who does it | What the documents must give them |
|---|---|---|
| Building official inspections | The building official or approved agency. | Approved drawings, with connection fire protection and rated joints shown clearly enough to inspect. |
| Special inspections | An approved special inspector, independent of the contractor and usually hired by the owner. | A statement of special inspections, plus connection, fastener, and anchor details with the installation requirements. |
| Structural observations | A registered design professional, often the structural engineer of record. | Structural drawings and reviewed shop drawings that show member locations, sizes, and grades. |
| Off-site inspections | An approved inspector at the fabrication facility, when the project inspector cannot attend. | Requirements for prefabricated assemblies such as rib panels or timber-concrete composite floors. |
| Moisture and protection observations | Usually the architect or envelope consultant. | The moisture management plan and protection requirements in the specifications. |
Nine checks before construction starts
- Statement of special inspections. Confirm the set includes one project-specific statement that covers the mass timber items, not only a generic template. The paper notes that templates may leave out mass timber inspections.
- Connection details. Check that each connection the statement lists has a detail with fastener type, length, spacing, angle, and any pre-drilling requirement.
- Concealed connections. Confirm the drawings show how concealed connectors and their fire protection can be inspected before they are covered.
- Fire-rated sealants. Where sealants or adhesives form part of a rated assembly at panel joints or intersections, check that the specifications name them so they can be inspected.
- Product standards. Check that CLT and glulam are specified to their product standards, ANSI/APA PRG 320 and ANSI A190.1. The paper notes these are not treated as fabricated items, while NLT and DLT may be.
- Off-site work. Identify any assembly made off site, such as timber-concrete composite floors, and confirm the documents say who inspects it there.
- Labels and orientation. Confirm the specifications require grade stamps or piece labels so the inspector can check that the right member is installed the right way.
- Inspection access. Look at the sequence. Work must remain visible and accessible for inspection until it is approved, so ceilings, toppings, and encapsulation must wait.
- Preconstruction meeting. Check that the specifications require a preconstruction meeting with the owner, contractor, supplier, installer, design team, special inspector, and building official.
Published example: an unclear governing revision
This finding comes from a mixed-use residential project that was not mass timber. In the published governing-revision finding, two structural schedules carried different requirements, and the set did not make clear which version governed.
Inspectors check work against the approved construction documents. When two schedules disagree, an inspector cannot tell which fastener pattern or connection to accept. On a mass timber project, resolve that kind of conflict before inspections begin.
Where Groundbook fits
Upload the architectural, structural, and MEP drawings with the relevant specification sections, and run a cross-discipline review. Groundbook flags potential disagreements, such as an opening shown on an MEP plan but missing from the structural panel layout, with links to each source sheet. Your team decides what each finding means for the fabrication package. Groundbook does not check structural capacity, fire ratings, or the fabricator’s model.