Podium-style mixed-use developments are popular in urban environments due to their versatility and efficient use of space. These structures allow developers to combine residential and commercial spaces within a single footprint, maximizing the use of available land.

Typically, these buildings consist of a concrete “podium” foundation that supports several levels of wood-framed residential units above. While this design offers advantages, it also presents unique obstacles, particularly in the construction and electrical wiring processes. This case study explores some of the recurring pitfalls associated with podium-style construction, drawing on my experiences as an electrician, authority having jurisdiction (AHJ) and educator.

Defining podium-style construction

A podium-style building combines different construction types to create a single structure. The lower levels, often designated for commercial retail or office spaces, are built using Type I fire-resistive concrete construction methods. Above the podium, three to five stories are constructed using Type III or Type V wood-framed construction for residential dwelling units or hotel rooms. This blend of construction types provides a cost-effective alternative for large structures (up to 85 feet tall) without requiring the entire building to use more expensive Type I concrete construction.

Understanding construction types

To effectively address the challenges of wiring podium-style buildings, it’s essential to understand the various construction types in project plans and building codes.

• Type I construction: This fire-resistive construction type requires all structural and most interior elements be noncombustible. There is generally no limit on the number of stories in Type I construction.
• Type II construction: Known as “noncombustible construction,” this type uses materials like steel and concrete that do not ignite, burn or contribute to the building’s fuel load, reducing the risk of fire spread.
• Type III construction: Often referred to as “ordinary construction,” this type uses materials such as wood framing, plaster and brick. These materials are not considered fire-­resistant and typically require additional fire safety measures such as sprinkler systems or fire-resistant coatings.
• Type IV construction: This “heavy timber construction” uses large dimensional timber as the primary structural support. Heavy timber is known for its strength and natural resistance to fire, as it chars on the outside, insulating the wood and slowing the spread of fire.
• Type V construction: Also called “wood-framed construction,” this type uses dimensional lumber, wooden panels and engineered wood members as the primary structural elements. It is primarily used in residential and light commercial buildings due to its cost-effectiveness and ease of installation.

Wiring challenges

Each construction type has a specific level of expected fire resistance. As combustible properties increase, so do the limitations and the need for additional fire protection methods. These requirements are the genesis of many challenges encountered when wiring podium-style buildings.

One of the primary challenges an electrical contractor faces relates to the installation of wiring methods in areas requiring fire separation between different construction types. The routing of wiring often involves creating openings in walls, ceilings or floors designed to maintain fire separation. Additionally, the selection of the appropriate wiring method is critical. Wiring methods commonly used in wood-framed construction (Types III, IV or V) may not be permitted in areas of the building constructed using Type I methods. Certain wiring methods may lack the necessary fire-resistive properties or even increase the building’s fire fuel load.

For example, service-entrance (Style R) or SER cable is often used to bring the main power feeder from the lower-level service location to the upper residential levels. However, using exposed SER cable in areas built with Type I construction can be a costly mistake, as it is not permitted in these areas without proper fire-rated protection.

Code compliance

When installed in a strut support system or cable tray, SER cable is a commonly used wiring method for the main power feeder in podium-style buildings. While Article 338 of the NEC does not prohibit the use of SER cable in Type I construction, Section 338.10(4)(A) specifies that SER cable is permitted for interior branch circuits or feeders in compliance with Part II of Article 334, excluding Section 334.80. Part II of Article 334 provides the installation requirements for nonmetallic (NM) cable. Specifically, Section 334.10 indicates that NM cable (and SER cable by reference) is only permitted in structures of Types III, IV and V construction, and not in Type I construction.

If SER cable is mistakenly installed in Type I construction areas, options for remediation include installing the SER cable in a raceway permitted for Type I construction or selecting an entirely different wiring method that is permitted for the location.

Lessons learned

When a project’s profitability is significantly impacted by a Code violation, it can often be traced back to the following lessons:

• Training: Continuous education and training on electrical codes is essential. The electrical industry is constantly evolving to accommodate modern construction methods, and staying informed about all relevant codes and standards is crucial.
• Thorough Code review: A thorough review of applicable Code sections is imperative. The applicability of a Code requirement is not always obvious, and multiple sections of the NEC may need to be reviewed to understand the full requirement. Missing a critical detail can be costly.
• Communication: The AHJ plays a crucial role in the success of a project. Do not hesitate to ask questions during the plan review process or reach out to the inspector with concerns. Inspectors generally want to see your project succeed and can provide valuable guidance.

Conclusion

Podium-style mixed-use developments offer a versatile solution for urban living, combining residential and commercial spaces in a single structure. However, their construction and wiring present challenges that require careful planning, coordination and attention to detail. From structural complexities and fire safety concerns to electrical wiring, each aspect of the project must be meticulously managed to ensure a successful outcome. By understanding these challenges and implementing best practices, electrical contractors can deliver buildings that are safe, efficient and sustainable, meeting the needs of residents and businesses.

stock.adobe.com / hanohiki