The increasing demand for energy-efficient and modular housing has led to innovative

approaches to airflow and ventilation. This white paper explores an optimized airflow strategy for

a fourplex unit built using Structural Insulated Panels (SIPs). The central challenge is ensuring

proper ventilation, fresh air intake, and dehumidification, particularly in high-humidity climates like

Mobile, Alabama.

already included in the provisional patent for the Fully Integrated Reinforced Modular SIP

System (FIRM). The patent describes a centralized chase system that houses HVAC, electrical,

plumbing, and sprinklers, minimizing redundancy and optimizing space usage. The airflow

system proposed here enhances this approach by integrating exhaust ventilation, passive fresh

air intake, and humidity control.

2. Airflow Required

5. Utility Chase and Pipe Sizing Considerations

● Overall Dimensions: 24” x 24” (losing 3” for interior cladding).

● Dedicated Exhaust & Drainage Paths:

● Fire-resistant lining inside the chase ensures code compliance and longevity.

6. Mini-Split HVAC System Integration

● Smaller diameter ductwork for air conditioning enhances efficiency.

● Insulated refrigerant lines improve energy conservation.

preventing heat gain in cooling mode and heat loss in heating mode.

● Space-Saving Installation: Smaller ducts are easier to route within SIP walls and ceilings

without requiring large cavities.

● Better Air Pressure Management: Small ducts help maintain velocity in distributed

systems, allowing air to reach farthest rooms without significant loss of pressure.

● Reduced Material Costs: Requires less material per linear foot, resulting in cost savings

and fewer fittings.

Challenges of Small-Diameter Ducts

● Potential Airflow Restriction: If ducts are too small, airflow resistance increases, leading

to higher fan power requirements.

drilling at an angle or pre-cutting channels. However, return ducts at 6 inches or larger pose

structural challenges.

A proposed manufacturing adaptation involves:

● Positioning insulation layers above and below the duct to maintain thermal performance.

● Bonding the SIP layers together without compromising structural integrity.

This method would allow seamless duct integration within the SIP structure while maintaining

its load-bearing capabilities. If this technique is not commercially available, it may require

innovation to become a standard approach for modular SIP construction.

7. Maintenance and Future-Proofing the System

8. Conclusion

This ventilation strategy leverages a combination of passive airflow, mechanical assistance, and

smart intake/exhaust routing to ensure efficient indoor air quality while preventing

cross-contamination of odors. The proposed system prioritizes energy efficiency, ease of

maintenance, and future scalability.

1. Prototype and test a single-unit version of the system.

2. Conduct airflow performance assessments.

3. Validate the efficiency of the 12-inch shared exhaust stack.

4. Optimize heat pump integration and evaluate operational costs.

Insulated Panel (SIP)-based fourplex presents an opportunity to streamline installation, reduce

material costs, and simplify maintenance. This white paper explores strategies to efficiently

design and implement plumbing within the shared chase while ensuring optimal performance,

ease of maintenance, and minimal structural disruption.

2. Plumbing Supply Distribution

● The main water supply will run vertically through the existing central chase, either from

the ground level up or from the roof down.

● Cold and hot water supply lines will be routed separately within the chase to avoid any

cross-contamination or temperature interference.

● No centralized hot water system: Each unit will have two independent tankless water

heaters, one for the kitchen and one for the bathroom.

3. Drainage & Venting Strategy

● A 4-inch central drain stack will manage wastewater from all units.

● Each unit’s fixtures (sinks, toilets, showers) will connect to the shared vertical drain stack.

● The central chase itself is pre-cut, and only the branch lines will need to penetrate the

SIP floors, reducing disruption to the SIP structure.

ensuring no risk of intermingling between sewer gases and ventilation air.

● AAVs (Air Admittance Valves) or dedicated vent stacks will be used to prevent sewer

gas buildup and allow proper drainage airflow.

● Accessible cleanout ports will be installed at each floor level.

● A straight vertical pipe system ensures gravity-fed drainage with minimal risk of clogs.

4. SIP Panel Adaptations for Plumbing

● Water supply lines will run vertically within the central chase, ensuring efficient

distribution to all units.

● Pipes will be insulated to prevent condensation and freezing risks.