Lesson 14: Building Materials: Concrete, Masonry, Steel, and Wood

Reading

The IBC does not contain a full design manual for each structural material. Chapters 19, 21, 22 and 23 mostly do something more useful for an inspector: they name the standard that governs each material, add the code's own amendments, and set a handful of rules that show up on every job site. Concrete, masonry, steel and wood each have their own referenced standard, and the edition matters because the plans are checked against the edition the code names. This lesson gives you the map of what each chapter points to and what to look at in the field, and it previews the special inspection link that Lesson 16 finishes.

Referenced standards and their editions

Chapter 35 lists the standards the 2021 IBC adopts by reference. The editions below were read from the code text. Remember that a city can adopt a different edition of the IBC or amend these chapters, so confirm what your jurisdiction has adopted.

One trap to avoid: structural welding of steel shapes is reached through the AISC specification named in Section 2205.1, so do not tell a contractor that a particular AWS structural welding code is directly named by the IBC. Only the reinforcing bar welding code is listed under AWS in Chapter 35.

Concrete: Chapter 19

Section 1901.2 says structural concrete is designed and built under Chapter 19 and ACI 318 as amended by Section 1905. Slabs on grade are outside Chapter 19 except for Sections 1904 and 1907 unless they carry vertical or lateral loads from the structure, so a plain warehouse floor and a slab that supports a bearing wall are different cases. Section 1901.3 sends anchoring to concrete to ACI 318 as amended in 1905. Section 1906 covers footings for light-frame construction and Section 1908 sends shotcrete to ACI 318. The chapter's other sections are durability (1904), tests and materials (1903) and minimum slab provisions (1907).

In the field the inspector is checking the work against the approved plans and the specification: the formwork and its shoring, the size, spacing, splicing and cover of the reinforcement before the pour, the anchors and embedded items, and the pour itself. Concrete cylinders and slump tests and the special inspection of the pour are items for the special inspector under Section 1705.3, which Lesson 16 covers. The building inspector's job is to see that the steel was in the forms and correct before the concrete truck arrived.

Masonry: Chapter 21

Section 2103.1 requires masonry units, whether concrete, clay or shale, stone, glass unit or autoclaved aerated concrete, to comply with Article 2.3 of TMS 602. Section 2104.1 requires masonry construction to follow TMS 602 or TMS 604, and TMS 604 is only the installation standard for architectural cast stone, not a general masonry standard. Section 2104.1.1 says masonry is not supported on wood girders or other wood construction except as permitted by Section 2304.12. Section 2105 covers quality assurance, and the special inspection tie comes through Section 1705.4.

For a reinforced concrete masonry wall the inspection points are the vertical bars and their laps, the horizontal reinforcement, cleanouts at the bottom of tall grouted cells, grout placement and consolidation, and mortar and joint quality. Empty cells that should be filled and bars off center are the usual findings.

Steel: Chapter 22

Chapter 22 is organized in a way that is easy to mix up. Section 2202 covers identification of steel, Section 2203 covers protection (painting and corrosion), Section 2204 covers connections, and Section 2205 covers structural steel design, fabrication and erection under AISC 360, with Section 2205.2 sending seismic requirements to AISC 341 where required. Section 2204 says welding and bolting follow the specifications named in the chapter's later sections, with special inspection of welding and high-strength bolts under Section 1705.2. Section 2204.3 says anchor rods are installed per the approved construction documents with their threaded ends fully engaging the nuts.

The field checks that show up on almost every steel job are mill certificates and member markings that match the plans, base plates set on the anchor rods with full nut engagement, bolted connections with the specified bolt type and pretensioning method, and welds that are the specified size and length. Section 2207 covers steel joists, and Sections 2210 and 2211 cover cold-formed steel framing.

Wood: Chapter 23

Section 2302 covers design requirements and Section 2303 covers minimum standards and quality. The general construction requirements are in Section 2304. Two are worth knowing by number. Section 2304.10.2 requires the number and size of fasteners in a connection to be not less than Table 2304.10.2, the fastening schedule. That table was Table 2304.10.1 in the 2018 IBC, which matters if you are reading an older handout. Section 2304.10.4 covers joist hangers and framing anchors, and Section 2304.10.6.1 covers corrosion resistance for fasteners and connectors used with preservative-treated wood.

Protection against decay and termites

Section 2304.12 is one of the most inspected wood provisions in the Gulf Coast climate. Section 2304.12.1 requires naturally durable wood or wood treated with waterborne preservatives (under the AWPA U1 standard) in these cases:

• joists or wood structural floors closer than 18 in., or girders closer than 12 in., to exposed ground in crawl spaces or unexcavated areas inside the foundation perimeter (2304.12.1.1);
• wood framing and sheathing in contact with exterior foundation walls and less than 8 in. from exposed earth (2304.12.1.2);
• sleepers and sills on a concrete or masonry slab in direct contact with earth (2304.12.1.4); and
• wood siding with less than 6 in. clearance to earth, or less than 2 in. vertical clearance from concrete steps, porch slabs and patio slabs (2304.12.1.5).

Section 2304.12.2 adds a half inch of air space on the top, sides and end of girders that bear in exterior masonry or concrete walls, treated wood for posts on slabs in contact with earth, ground-contact treatment for wood in contact with the ground (2304.12.2.6), and termite-resistant or treated wood in areas of very heavy termite infestation (2304.12.2.7). Crawl space ventilation itself is in Section 1202.4, not in Chapter 23.

A worked example on clearances. A crawl space under a small addition has joists whose bottoms measure 15 in. above the exposed soil, and a girder whose bottom measures 14 in. above it. The joists are closer than 18 in., so they must be naturally durable or preservative-treated. The girder is not closer than 12 in., so the girder alone does not require treatment by this rule. The same assembly built with 20 in. under the joists would need no treatment under 2304.12.1.1.

Conventional light-frame construction limits

Section 2308 lets certain light-frame buildings be built without engineered design, but only inside limits. Section 2308.1 sends detached one- and two-family dwellings and townhouses up to three stories with separate means of egress to the IRC. The main limits under Section 2308.2 are stories by seismic design category (three stories in categories A and B, two in C, one in D and E), a floor-to-floor height of 11 ft 7 in., a stud height of 10 ft in bearing walls, average dead load of 15 psf, floor live load of 40 psf, ground snow load of 50 psf, a basic wind speed not over 130 mph (with a 140 mph exception in Exposure B outside hurricane-prone regions), and a span limit of 40 ft for ceiling joists, rafters and trusses between vertical supports. A building outside these limits needs engineered design, so a three-story apartment building in Seismic Design Category D, which allows one story, is not a Section 2308 building.

Where special inspections come in

Each of these materials also has a special inspection entry in Chapter 17: steel in Section 1705.2, concrete in Section 1705.3 and masonry in Section 1705.4. Those are performed by an approved special inspector rather than by the building inspector, and they are recorded in a report. The building inspector should know when the special inspector is due, because a missed concrete pour or a covered weld cannot be inspected after the fact. Lesson 16 covers the details.

Practice questions

Glossary

Referenced standard

A document such as ACI 318 or TMS 602 that the IBC adopts by name and edition in Chapter 35.

ACI 318

The concrete design standard that Chapter 19 adopts, in the 2019 edition, as amended by Section 1905.

TMS 602

The specification for masonry structures, covering materials and construction, named in Sections 2103 and 2104.

AISC 360

The structural steel specification that Section 2205.1 uses for design, fabrication and erection.

Anchor rod

A threaded rod cast or drilled into concrete or masonry to hold a steel base plate or connection.

Fastening schedule

Table 2304.10.2, the minimum number and size of fasteners for common wood connections.

Preservative-treated wood

Lumber treated with preservatives, with the treatment marked on the wood, used where decay or termites are a risk.

Conventional light-frame construction

Section 2308 wood framing that may be built without engineered design when the building stays inside its story, height, load and wind limits.