34 | SUMMER 2019 ADVANTAGE STEEL FEATURE Tolerances Crucial to the success of any PPVC building are extremely tight tolerances in the modules so that erection is quick and accurate, making structural steel an ideal material choice due to its dimensional stability and the precision fabricators can achieve. The horizontal and vertical interconnection of modules in particular pose a challenge as they need to not only have tight tolerances, but they must also transfer lateral and gravity forces between modules. Fabricators can solve this problem through custom connections or steel castings. One example of a casting that the authors have experience with is the propriety Z Modular’s VectorBloc system, as seen in Figure 2a, where a cast node not only forms a robust connection point for perimeter beams and columns but also allows modules to be fastened together efficiently. The configuration in Figure 2b is just one possible VectorBloc module-to-module connection; many other configurations are possible with different types of VectorBlocs which gives designers increased freedom in developing their PPVC building. Approvals Process PPVC generally requires an approvals process that is different from site-built construction projects. The challenge for PPVC from an approval’s perspective is that modules may be fabricated in a different jurisdiction than where they are ultimately erected. In general, the requirement is that the modules be designed and constructed to comply with codes and regulations in force at the installation location. However, it can often be difficult to determine whether a module complies with these requirements since many wall, roof and floor assemblies are closed-in when the module arrives on site, hindering inspection. To address this problem, many U.S. states require modular or factory-built building components to be reviewed and certified at the state level by a state-certified third-party agency. The responsible state department may also have further specific requirements that regulate the design, approval and inspection of the building at the manufacturing plant, the extent and cost of which can vary from state to state. In Canada, CSA A277, Procedure for Factory Certification of Buildings, relies on an independent certification agency for the assurances to the authorities at the final site that the manufactured elements comply with the code. Transportation requirements are also regulated at the state/province level, each of which have differing codes, permitting, lead cars requirements, and associated fee structures. As mentioned above, modular buildings must still meet local building codes. From a fire safety standpoint this typically requires floors and walls to have fire-resistance ratings. What is unique about modular buildings is that the structure from adjacent modules can fall within the assembly. In floors, for example, it is not uncommon for the roof structure of the lower module to support the ceiling while the floor of the upper module supports all finishes and floor loads. There is currently a dearth of available UL-tested assemblies that have dual structures like this, which means designers have few options and must either undertake an Engineering Judgement on an existingassemblyorperformfull-scaletesting on their own modular assembly. Additionally, many jurisdictions put a limit on the height and area of combustible construction, making structural steel the only feasible non-combustible structural material for large modular buildings without going through the alternative solutions process required for tall timber construction. FIGURE 2A: Pictures of Z Modular VectorBloc modular construction system. FIGURE 2B: Diagrammatic of Z Modular VectorBloc modular construction system. Image courtesy of Z modular. “Aprefabricatedmodularbuildingdoesnotneed tolookandfeel‘boxy’orcompletelyrectilinear whencomplete.Acompetentandexperienced designteamcancreateexpressivearchitectureand variedinteriorspaceswhileachievingthebenefits offeredinprefabricatedmodularconstruction.”