Commercial Plumbing Design Guide: Key Considerations for Engineers and Architects

Gravity drainage depends on pipes maintaining a continuous downward slope at a specified grade. This requirement can become a significant challenge below grade, where existing foundations, utilities, structural elements, bedrock or variations in site elevation may limit the available space for properly sloped piping. Vacuum systems can help overcome these constraints by reducing reliance on gravity and providing greater flexibility in routing underground drainage piping. 

Gravity Drainage vs. Vacuum Drainage

Gravity Drainage Systems – The traditional gravity drainage system uses gravity to move wastewater and waste down pipes to a municipal main or a lower sewage site.

Vacuum Drainage Systems – A vacuum drainage system utilizes negative pressure to move waste and wastewater through a closed network of pipes. Unlike a gravity-based system, it can move waste against gravity, around obstacles, including up slopes or even vertically.

Both have their advantages and disadvantages, depending on the nature of the project. Here’s a look at common questions and considerations.

Is the project a new-build or a conversion/adaptive use?

In most settings, traditional gravity-based plumbing is the most common approach to wastewater removal. Although gravity systems have been used successfully for centuries, they require careful engineering. In renovation projects especially, maintaining the continuous downward slope needed for proper drainage can present significant design challenges.

In situations where design constraints, sustainability goals, or renovation challenges are priorities, vacuum drainage systems offer several advantages over conventional gravity systems. These include:

• Greater design flexibility
• Reliable performance
• Simplified renovations
• Water savings and improved hygiene
• End-user advantages such as faster, cleaner restrooms, easier maintenance, quieter, and more hygienic.

Are there terrain or geographic complexities?

Gravity drainage depends on pipes maintaining a continuous downward slope at a specific grade. This requirement can become a significant challenge below grade where existing foundations, utilities, structural elements, bedrock, or variations in site elevation may limit the available space for properly sloped piping. Vacuum systems can help overcome these constraints by reducing the reliance on gravity and providing greater flexibility in routing underground drainage piping.

Because of their flexibility, vacuum drainage systems are often desirable when there are terrain issues. These include, but are not limited to:

• Bedrock or rock obstruction – can require blasting or cutting through dense rock, which can increase costs and difficulty for deep pipe alignment.
• Insufficient slope – a lack of a natural downward gradient, usually ¼ inch per foot drop for small pipes, can slow or halt movement of waste and water.
• Excessive slope – steep or hilly terrain can cause excessive velocity, resulting in the liquids separating from the solids, leaving the solid waste behind; large elevation drops can also create extreme hydrostatic pressure at lower levels, increasing the risk of damaged pipes.
• Shifting ground – areas where there is shifting clay, erosion, or significant freeze-thaw cycles can damage pipes, causing low pooling spots that collect waste and sludge.
• High water table – in areas with high water tables, dewatering, the process of removing water and stabilizing trenches, can be a significant challenge. Vacuum drainage systems reduce or, in some cases, eliminate the need for dewatering and trench stabilization.

For remodeling projects, vacuum plumbing systems may solve problems related to:

• Inappropriate inverts – In other words, inappropriate or incorrect piping, which disrupts gravity flow. This requires a major redesign, significant demolition and construction, or a workaround such as a vacuum drainage system.

• Difficult structural elements – Examples include post-tension slab foundations (slab-on-grade reinforced with high-steel cables encased in plastic sheeting), central steel columns, primary concrete piers, and lateral-resistance shear walls, all of which require high cost, effort, and time to modify.

• Historical building categorization – Historical structures often have restrictions on what can be changed; vacuum plumbing system benefits include: No gravity slope required; No floor trenching needed; Protects historic flooring, tiles, and structural foundations; Bypass hazardous materials, such as asbestos.

A gravity-based plumbing system may be preferable for:

• New-build projects (standard low-rise) — These projects typically have short pipe runs, straightforward layouts, and reliable water and sewer access. Gravity-based drainage offers relatively low upfront costs and conventional installation and maintenance.
• Residential projects with traditional layouts (suburban) — These projects typically have ample land, conventional sewer access, and standardized designs. Gravity-based plumbing and wastewater systems integrate well with existing infrastructure and provide predictable, straightforward operation.

A vacuum-based plumbing system may be preferable for:

• Adaptive reuse and conversions — Existing buildings may have structural constraints, historical-preservation requirements, or limited opportunities for adding plumbing stacks and other infrastructure. Vacuum systems can provide a flexible, lower-impact retrofit option.
• High-rise and dense urban settings — Projects with long vertical runs, limited service space, or challenging routing can benefit from vacuum technology, which can transport wastewater efficiently while reducing the amount of conventional infrastructure required.
• Healthcare and institutional facilities — These facilities often require high standards of hygiene, controlled flushing, and reliable drainage performance. Vacuum systems can support water-efficient operation while helping reduce blockages and the potential for improper use.
• Stadiums, arenas, and event venues — High-occupancy facilities experience significant fluctuations and peaks in demand. Vacuum systems can help manage these demands while reducing water consumption and supporting rapid, reliable drainage.
• Remote and off-grid sites — Where municipal water and sewer networks are unavailable or difficult to access, vacuum systems can provide greater flexibility in system design, improved water efficiency, and compatibility with decentralized or self-contained treatment. They can also be advantageous on hilly, rocky, or otherwise challenging terrain.
• Sustainability-focused projects — Projects pursuing aggressive water- and energy-efficiency goals or certifications such as LEED, BREEAM, or WELL* may benefit from vacuum plumbing. By using substantially less water for flushing and enabling more flexible system layouts, vacuum technology can contribute to overall resource efficiency and potentially reduce a building’s environmental footprint.

Additional Considerations for Engineers and Architects

Broadly, when planning projects, considerations about vacuum-based plumbing systems versus gravity-based plumbing systems include:

• Early multi-disciplinary coordination. It is important to coordinate and align mechanical, electrical, and plumbing design early in a project to avoid spatial complications and expensive retrofits.
• Occupancy-based sizing. Standards such as REHVA, ASHRAE** or local building codes should be considered to size fixtures accurately based on maximum occupant loads instead of over-designing infrastructure.
• Specialized facility demands. Consider unique space and equipment needs for projects, such as specialized medical gas lines for healthcare spaces and grease interceptors for commercial kitchens.
• Sustainability and efficiency. To meet LEED certification credits or other sustainability certifications, consider integrating low-flow fixtures, wastewater recycling loops, or rainwater harvesting implementation.
• Accessibility and maintenance. Locate shut-off valves, cleanouts, and mechanical chases with accessibility in mind to simplify maintenance and repairs, and future tenant buildouts.

There is a lot for engineers and architects to consider when planning a new project. Vacuum drainage systems aren’t the right solution for every construction or remodeling project. But for many projects, they can be the perfect solution for common challenges.

To learn more about Evac’s line of total vacuum solutions, contact us today!