6 Considerations for Ensuring Proper Airflow in Modular Builds

Airflow is a crucial consideration for any project. Too little will lead to inefficient HVAC operations and airborne health hazards, while too much will introduce external hazards like mold and further limit HVAC efficacy. These complications deserve attention in all construction, but modular builds face unique challenges.

Modular construction inherently produces gaps between units that introduce new insulation and airflow considerations. The materials you'll often see in these builds may also impact airflow differently from more conventional alternatives. 

While these factors may make modular building airflow tricky, they don't mean it's impossible. Here are six things to keep in mind to ensure your modular projects have proper airflow.

1. Local Building Codes

Before taking any other factor into consideration, you need to go over any applicable building codes. These regulations will set a baseline for acceptable airflow you can target through other strategies.

The CDC recommends you achieve five air changes per hour (ACH) in most cases. Many building laws set the bar much lower, but officials developed these standards before the COVID-19 pandemic put a spotlight on airborne contaminants. Laws are unlikely to become less stringent in this area, so you're better off aiming for the CDC's higher standard than playing it closer to a smaller minimum ACH level.

Since modular buildings are most common in apartment buildings or quick expansions to medical and industrial facilities, you should take high occupancy concerns into account. The higher your expected occupancy, the higher your ACH should be.

2. Industry-Specific Regulations

Similarly, you should also keep unique industry standards in mind. Depending on the kind of building you're designing, you may face additional airflow requirements. These are often more stringent than general building codes.

Medical facilities and research labs are great examples of modular structures with these tighter regulations. Operating rooms need at least 20 ACH and must have positive air pressure in relation to any adjacent rooms. That can be difficult to achieve with modular boxes unless you keep it in mind from the very beginning, as you must consider the layout of each module concerning each other.

Remember that airflow regulations can cover more than just the rate of airflow. The direction and air pressure may also matter. For example, cleanrooms with high contamination concerns typically use unidirectional airflow to minimize airborne contaminants. Less sensitive cleanrooms — such as those in packaging — may use non-unidirectional airflow, where the air moves in different directions. Combining the two practices through mixed airflow helps balance contamination and temperature concerns, ideal for medical device assembly. 

3. Material Selection

Modular projects also need to consider how their materials impact their airflow. Some materials let more air through, making it difficult to maintain desired internal airflow while keeping natural airflow out. Others may produce airborne contaminants that raise the ACH standards you should aim for.

Pressed wood — more common in modular builds than conventional projects — may contain higher formaldehyde concentrations than other materials. This chemical leaks through the wood through off-gassing for a period after construction, posing inhalation risks. Consequently, if you’re using pressed wood, you must ensure a higher ACH and, ideally, unilateral airflow.

It’s also worth considering how modular builds are inherently more susceptible to mold and mildew growth thanks to the cavities between units. You can minimize these airborne contaminant risks through moisture-resistant materials like glass, synthetic rubber waterproofing or pressure-treated lumber.

4. Increased Hazards from Interstitial Spaces

Most airflow considerations focus on enabling appropriate mechanical ventilation. However, you also need to think about the kinds of airflow you don’t want. More specifically, you’ll need to address the problem of natural ventilation and moisture buildup in modular projects’ interstitial spaces.

Placing modules together naturally creates relatively large interstitial spaces. These cavities enable airflow between walls and ceilings, leading to moisture buildup and, in turn, mold and mildew growth. Addressing these concerns after the fact can be difficult, so it’s best to tackle them from the start.

You can direct air away from interstitial spaces through positive or negative air pressure in hazard-prone areas. The ideal option depends on the kind of space you’re dealing with and the climate. Ensuring you insulate joints between modular boxes well will help, too.

5. Ongoing Maintenance

Even with these other protections, interstitial moisture buildup can still occur. Plus, all HVAC systems eventually need repair. Compared to conventional builds, though, modular projects can make it difficult to access these spaces, which deserves correction.

Keep future maintenance in mind when designing modular buildings. You may need to install access doors and panels on module sides that you know will form a cavity between walls. Using BIM clash detection to highlight potential maintenance issues can help address problems before they arise.

Operation and maintenance account for 75%-80% of a building’s lifetime costs and can cause significant disruption. As an architect, you should aim to make these processes as easy and cost-effective as possible to impress future clientele. Making modular buildings more accessible to repair personnel and passing BIM models along to property managers will help.

6. Whole-Project Simulation

Finally, it’s important to think of airflow on a building-wide scale. That’s easy enough for conventional builds but is easier to miss when tackling modular projects. Only focusing on individual modules’ airflow may be simpler, but it’ll likely create problems with relative air pressure and airflow between rooms.

While fabrication should still tackle these projects on a module-by-module basis, the same doesn’t go for design. As you model individual boxes, consider how they will align with each other. Use BIM software to simulate the finished project and model airflow between rooms to highlight any potential issues.

This whole-project simulation will take more time in the design phase, but it’ll prevent rework and maintenance concerns in the future. Extensive BIM usage can also cut project timelines by 50%, making up for these more time-consuming simulations.

Modular Build Airflow Is Challenging But Essential

Ensuring proper airflow can be challenging in any project. The nature of modular construction can make it even harder, but that just means that it deserves more attention. You can address these concerns and provide sufficient airflow if you know what to look out for.

Paying attention to these six considerations will help you design and build better-ventilated modular projects. Doing so protects the buildings’ future occupants, prevents regulatory fines and can impress future clientele to help grow your business.