Written by: Adam Cross, Plumbing Design Controller
The construction of a new building requires the design and implementation of several sophisticated systems, many of which have significant overlap with the facility’s plumbing. To ensure that the design of these systems are correct, especially when the level of complexity is high, it is paramount to consider many items. Below are just a few items that we assist clients with when it comes to plumbing design to ensure more efficient and sustainable water use and a more environmentally-friendly facility.
Top Considerations For Plumbing Design
- What is the building use? For example, is it a restaurant, an apartment building, or a senior living facility?
Knowing the intended use of a building will not only determine the type of plumbing system, but also the need for any special equipment, like interceptors or sump pumps. For example, a senior-living facility may need a central boiler system for more efficient delivery and maintenance of the hot water system, whereas a restaurant may require several water heaters ganged together for quick hot water recovery.
- What are the governing plumbing and natural gas codes for that location?
The governing codes will determine the design and what type of systems/equipment may or may not be allowed by the Local Authority Having Jurisdiction (LAHJ). For example, the LAHJ may not allow a single grease interceptor for a multi-tenant retail building, in which case the design of multiple small grease interceptors should be taken into account.
- Where are the utility hookups for the domestic water and sanitary sewer services located on site?
Usually, a plumbing engineer only extends the design 5 feet outside the building. Because of this, it is key to know precisely where to bring the domestic water and sanitary sewer services into and out of the building for connection to public systems. This factor will drive the design.
- What is the domestic water pressure coming from the street?
Correct pressure ensures that each plumbing fixture operates properly. Obtaining proper pressure is important to avoid a domestic booster pump, adding cost to the project.
- What size does the building’s incoming water line need to be in order to meet the maximum GPM (gallons per minute) on all the plumbing fixtures inside the building?
It’s critical that the incoming water line is the right size so that all the plumbing fixtures in the building get an adequate supply of water to operate. It’s also important to ensure that the incoming water line is not larger than the size of the site water line coming from the street. If this were to happen, the site water line would not provide an adequate amount of water per the building’s requirements. It is incumbent upon the building engineer and site civil engineer to coordinate the correct sized lines.
- What size does the main sanitary lateral need to be in order to properly discharge the sewage from the building?
Just as it’s critical that the incoming water line be the correct size, the outgoing sanitary main needs to be the proper size as well to ensure it can handle the building’s total sewage flow. If the sewer line is inadequate, the building’s sewage could potentially backup into the building.
- What is the invert of the public sanitary main coming from the street?
The sanitary sewer system is drained by gravity. A proper design ensures that the plumbing comes out of the building at a level that won’t inhibit this. If the design fails to do so, a sewage pump might be required in order to pump the building sewage to the same height as the site main, and result in more cost.
- How will you heat your water?
The hot water system design varies depending on the facility and its intended use. If it’s a senior living facility, then a centralized water heating system where all the water heaters are in a single room will offer a level of control and safety. Apartments can also use this system, but typically residents like to control their own water temperature, so a water heater is typical in each unit. The hot water system design for each type of building is different, so talking with the building owner about their plans for the building’s use and operation is important to help select the best system design.
- Will the HVAC system use gas or electricity for energy?
If the HVAC system uses natural gas, your plumbing engineers must know the gas consumption of the equipment and where the equipment is located. The further away from the building the gas meter is, the larger the pipe size must be in order to deliver the required BTUs/hr. It’s also imperative that the engineers know the delivery pressure the gas utility company is using to bring gas to the site. The larger the delivery pressure, the more BTUs can be delivered through a given pipe size.
- How will rain water be drained from the roof?
You might overlook roof drainage as scope of work under a plumbing engineer, but it’s an important component. A gallon of water weighs approximately 8.3 lbs. The structural design does not take that weight into account, so draining the water from the roof is paramount. Roof drains are usually the solution and the code listed rainfall rate for the location and capacity of the drains drives the design.
- What piping material is the domestic water and sanitary sewer piping going to be?
All piping material has its advantages and disadvantages. CPVC and PVC are cheaper than copper or cast iron, but it cracks easier. The selection often comes down to the expense a contractor incurs to install it. Having a plumbing engineer paying attention to the specifications and alerting you to the best piping material for your project/location can save in repairs down the road.
- Who selects the manufacturer and model number of the building’s plumbing fixtures?
Typically, standard makes and models are listed on the plans, but the actual selections depend on the project. Sometimes an interior designer or owner requests a specific model after the plumbing design is complete. If the chosen model does not match the specifications the plans were based upon, it can impact the project. It is helpful to have this information at the start of the plumbing design process to avoid any changes after the fact.
- If the project is an apartment building, where are the handicap accessible units (ADA units) going to be?
Handicap accessible units usually have a different bathroom layout than standard units of the same type in order to achieve the clearances required by accessibility code. The location of these units could impact the routing of the pipes because the fixtures and walls that the piping comes down in might not line up properly. Asking this question early on allows the plumbing engineer to encompass this need right from the get-go.
- If the project is a dental office, will there be any nitrous oxide?
When designing a dental space that utilizes nitrous oxide to sedate patients, MEP engineers account for this by first adding the oxygen and nitrogen lines to the dental chairs and ensuring the lines are the right size.
- If the project is a restaurant, where will the grease interceptor go?
One of the main differences in designing a restaurant from other facility types is the presence of a grease interceptor (GI). Greasy discharge from commercial kitchen sinks cannot drain directly into the building’s sanitary sewer system. This is due to the fact that once grease cools, it begins to solidify, creating blockages in the sanitary system. To combat this, grease waste must first pass through a grease interceptor. The interceptor will separate the grease, so it’s not present in the sewer system. One key factor in determining the design of the facility’s grease waste system is where the GI is located. It needs to be accessible for cleaning, so for that reason, it’s usually preferable to have them outside.
As you can see, there is a lot of thought that goes into the plumbing design of any facility. Having your MEP engineer on board at the inception of the project can avoid costly re-design and change orders down the line. We utilize a team approach to facility design to ensure that all systems work together and that a well-planned, economical building is delivered to you, the client.
About VP Engineering
VP Engineering is a full-service architectural engineering firm, serving clients throughout the U.S. and around the world. With experience in a wide range of building types, from housing to commercial, our MEP engineering services help keep projects on budget and achieve your goals. Learn more at vpce.com.