Commercial Drain Design

By Michael J. Whiteside

The beginnings of the modern specification drainage products can be traced the early 20th century. Architects began to demand a drain with secondary drainage to protect both the aesthetics and structural integrity of their buildings. Until this time, a drain was usually nothing more than a grate fitted into the end of a pipe, which terminated at the floor level. Unfortunately, this led to water seepage around the pipe and to the destruction of ceilings. A drain with secondary drainage meant that a drain body had to be designed to allowed weepholes to remove water that may seep around the rim of the drain. Since then, architects and mechanical designers have been able to specify products that featured various design considerations that were made necessary by the rapidly changing building techniques we have experienced since the beginning of the 20th century.

As we built both higher and faster, architects and engineers realized the need for a drain with not only secondary drainage, but also with a clamping device to secure a waterproofing membrane in multi-story buildings. These developments ushered in the era of competition in the specification drainage market, as new manufacturers duplicated and expanded on products that had been produced before.

More recently, the advent of the adjustable drain and the floor mounted fixture carrier for off-the-floor fixtures added to the large variety of specifiable products available to the architect and mechanical designer. Today, a specifier can choose from thousands of products from many manufacturers. A mechanical designer must be careful at every turn to ensure s/he has decided between nontilt or tractor grates; between ductile and gray cast iron; between adjustable and nonadjustable top assemblies; heel proof or nonheel proof grates. Furthermore, many factors concerning plumbing and building codes apply, therefore, it is recommended that they be consulted at the outset of selection and specification considerations. In summary, there is a large array of options for a mechanical designer to consider. Following are some key factors to consider when specifying floor and area drains: sizing, location requirements, floor construction, traffic conditions, drain top and outlet sizes, drain top, materials and appearance, trapping of sediment, backflow prevention, indirect waste, drain outlet connections.

Sizing

The potential volume of drainage to be accommodated by drains serving interior areas can, as a rule, be calculated with reasonable accuracy using the total amount of water within the area as a basis for sizing. The area's function as well as types of water use equipment used within the area must be considered. For example, a public restroom, with its numerous types of water use fixtures, must include drains sized and located to handle potential overflow due to stoppage as well as routine custodial waste from cleaning byproducts. In addition to plumbing fixtures, water requiring floor drainage emanates from man's sources such as run-off from vehicles in garage areas, condensate waste and processed water discharge from equipment hose stations and emergency drainage as from sprinkler systems or spills. It is good practice to provide floor drains in any area where a water source is located. Moreover, floor drains should be adequately sized and strategically located to avoid standing water, which is a potentially hazardous condition. Sizing of area drains for surfaces adjacent to the building is normally based on rainfall and size of the area to be drained. Placement of area drains depends on the topography of the area with drains placed at the low points were run-off is anticipated. Information concerning such sizing provided by the ASME Floor and Trench Drain Standard, A112.6.3.

Location Requirements

The locations within and adjacent to the building structure which require provisions for drainage are many. Some significant for which drains must be selected are toilet and shower rooms, boiler and equipment rooms, basements, garage and parking areas, kitchens, laundry, utility and service rooms, elevator pits, entry areas, machining and processing areas and refrigeration rooms. Drains should be considered and selected for any location where water is supplied and surface drainage must be accommodated.

Floor Construction

Floor construction has a distinct influence on drain selection and therefore must be considered at the outset of the selection process. Such elements as slab type and thickness, surface finish, depth of fill, waterproofing membrane and/or finishing materials will influence the selection.

Traffic Conditions

Once installed, floor drains become integral components of the floor or area in which they are located. Therefore, the drain selected for each installation must have tops or grates capable of sustaining the type of load to be supported by the floor. This is particularly significant where drains selected are installed in traffic locations. It is recognized that top-loading requirements vary with the location, type of construction and service conditions. These requirements for floor and area drains are addressed by the ASME Floor and Trench Drain Standard, A112.6.3 with the following five top loading classifications:

• Light duty: all grates that have a safe live load under 2,000 lbs.
• Medium duty: all grates that have a safe live load between 2,000 lbs. and 4,999 lbs.
• Heavy duty: all grates that have a safe live load between 5,000 lbs. and 7,499 lbs.
• Extra heavy duty: all grates that have a safe live load between 7,500 lbs. and 10,000 lbs.
• Special duty: all grates that have a safe live load over 10,000 lbs.

The safe live load is computed by dividing the load at failure by two when the grate is loaded in accordance with the test procedure stipulated in the standard. A 3 1/2 in. diameter platen is used during the load rating test and applied to the center of the grate. Using these top-loading classifications as a guide when loading requirements for the drains in a given location have been determined, the duty type required can be selected.

Drain Top & Outlet Sizes

A drain's top size, regardless of its shape, influences the number and size of openings between support members, which in total account for the grate's open or free area. Normally, the larger the top the greater the free area. Free area is the key factor used in evaluating the grate's ability to permit sufficient drainage to enter the drain for efficient use of the drainage system and prevent build-up of water on the floor or area served by the drain. Codes and standards stipulate that for proper drainage, interior floor drains should have a grate free area equal to 1 1/2 times the transverse area of the connecting pipe and exterior area drains, subject to rain-fall, 2 times that of the connecting pipe. Thus, it is important in the selection of floor and area drains to consider the top and outlet sizes as they relate to each other. Table 1, taken from ASME Floor and Trench Drain Standard, A112.6.3 provides at a glance the grate free area requirements for outlet sizes, thus connecting pipes, based on the ratios given.

Drain Top Materials & Appearance

Cast iron is the primary material used in the production of floor drain components. Floor and Area drains are typically cast in a gray cast iron with a tensile strength of 25,000 to 30,000 psi. The applicable ASTM specification is A-48-83, class 25. Cast ductile iron tractor grates are usually recommended according to duty type for most locations where service, more than appearance, is the determining factor. For example, warehouses, equipment rooms, garages, basements, and service and machine areas in locations where severe service conditions, such as shock or impact loading are factors. Beyond ductility, ductile iron as superior strength to regular cast iron. The combination of strength and ductility make ductile iron the logical choice for such locations. In addition to ductile iron grates for unfinished areas, adjustable strainers of Type CF8 (304) stainless steel and nickel bronze are available to match the floor area finish.

Trapping of Sediments

There are few, if any, floors and areas that are free of sediments, debris, and bits of non-liquid waste that gravitate to the floor drains. Such materials, if permitted to enter drains and drain lines unchecked, will inevitably lead to messy stoppage of the drain lines. Obviously, proper custodial maintenance of the locations will preclude excessive amounts of such materials from entering the drains. However, the presence of a certain amount of debris is unavoidable. Therefore, preventive measures should be taken to assure free drainage without stoppage. Sediment buckets or baskets may be used in areas such as washrooms and showers to intercept valuables and hair. Floor drains, area drains and catch basins which have indicated openings in their grates in excess of 3/8 in. should have secondary strainers or sediment buckets specified in areas where sediments may clog drain lines.

Backflow Prevention/Trap Seal Priming

Backflow through drains, a most undesirable and sometimes damaging condition, due to either clogged interior drain lines or overloaded sewers, can be effectively retained through employment of backwater valves. The most common type of backwater valve used in floor drains is the swing check and float types; either of which with the proper maintenance will perform effectively for the purpose intended. When selecting drains for locations below curb or street elevation, where gravity drainage to the main sewer is planned, backwater valves should be used in any locations where backflow conditions could develop. When considering backflow prevention, it is the logical time to also consider prevention of inflow or noxious sewer gas. Most codes specify that floor drains shall connect into a trap and that the trap seal be maintained to prevent the inflow of sewer gas. In locations where floor drains with integral traps or connected traps will be subject to infrequent use, evaporation loss of trap seal is probable. Therefore, such drains should be provided with trap seal primer connections, to permit hook-up of seal water replenishment piping from a trap seal primer valve to maintain the seal.

Indirect Waste

In locations where equipment will be producing indirect waste such as condensation, which cannot be piped directly into the drainage system, the drainage is normally directed to a floor drain through discharge piping terminating above the drain. In these locations, the floor drains should be equipped with funnels to direct the discharge into the drain and to avoid splashing. The remaining grate free area outside the funnel in such drains is open for normal floor drainage. Floor drains with funnels must not be installed in traffic areas. Round funnels accommodate drainage from a single indirect source, while oval funnels are designed to receive drainage from more than one source.

Drain Outlet Connections

Floor and area drains are available in several outlet connection types. The drain's outlet connection must be compatible with those of the drainage piping system to which it is connected. The most commonly employed connection types are: no-hub, push-on, threaded, inside caulk and PVC/ABS socket connection.

No-hub is the most widely used connection. A no-hub connection is achieved by butting no-hub soil pipe or plastic pipe to the bottom of the drain and securing it with a no hub coupling.

Push-on is a unique labor saving compression gasketed connection designed to simply push on the stub end of the pipe. The push-on drain body and gasket can be used with plastic, steel, no hub and service weight soil pipe.

Threaded connection bodies have a female threaded outlet that the waste pipe threads directly into for a secure connection.

The inside caulk drain outlet connection is a bottomless hub into which the drainage pipe is inserted. The bottom of the outlet is sealed with the oakum in the annular space between the pipe and the hub and the connection is then sealed with molten lead. Inside caulk connections are compatible with No-Hub, service weight and extra heavy soil pipe.

PVC/ABS socket weld connections are a proven installation time saver. They provide a sanitary connection to the piping system for specialized applications. 

Michael J. Whiteside is the owner of MIFAB Inc. 1321 W. 119th St., Chicago, IL, 60643; (773) 341-3001; Fax: (773) 341-3046; www.mifab.com. He has been with the company since 1992. He currently serves as vice president of the Plumbing and Drainage Institute (PDI). He can be contacted via e-mail at mwhiteside@mifab.com.