Does a prefabricated concrete restroom make sense for your facility?
Does a prefabricated concrete restroom make sense for your facility? Consider these factors.
By Chris Reese, Senior Engineer, Easi-Set
When planning for a new restroom facility many questions come into play. Can I combine it with other functions like a concession stand? What is more important, low initial investment or long-term value? How much maintenance will be required? Will it look good? Will it last? Let’s go through some details that will hopefully bring you closer to making an informed decision on whether a precast concrete building is the right choice for you.
What are the Risks for your location?
Wind Loads (windstorm) – In sustained winds or sudden thunderstorms broken tree branches and loose debris can become lethal projectiles. Even 75-85mph Category 1 Hurricanes can compromise weak structures like metal sheds and poorly constructed wooden buildings. Typical 3-inch steel-reinforced precast concrete walls can be designed to withstand wind speeds of 165 mph plus. Heavier walls, such as 4-inches, in combination with specialized doors, impact resistant windows and hardware will meet Miami-Dade hurricane standards of 185mph. Prefabricated concrete buildings can even be designed to meet ICC-500 and FEMA guidelines for Tornado and Hurricane Shelters (wind speeds range from 130 to 250 mph). These shelters are designed to shield debris hazards, including wind-borne missile impact resistance. Prefabricated concrete restrooms offer flexibility in accommodating various wind speed design criteria.
Tree Fall (impact resistance) – Winds combined with torrential rainfall can cause catastrophic damage to buildings and the people who seek shelter in them. A 50’ foot maple tree can easily weigh over 10,000 lbs., completely destroying typical site-built structures. All-precast concrete buildings have proven in real-life and test scenarios to be a durable solution to impact loads, playing a large role in building resilient facilities.
Snow Loads – 1 sq. ft. of wet snow can weigh 12.5 lbs., meaning just 12” of snow on a 10’ x 12’ roof equates to 1,500 lbs. On a 20’ x 50’ building, that’s over 6 tons. Designing for snow loads varies by area, region, and elevation. Depending on location, snow loads could be anywhere from negligible to exceeding 300 pounds-per-square foot in high snow areas. Pre-Engineered, pre-fabricated structures offer flexibility to accommodate various different design load requirements, eliminating the worry of structure collapse.
Floodplains - As required, prefabricated concrete buildings can be designed, constructed, connected, and anchored to resist floatation, collapse, and permanent lateral displacement due to flooding. Step down floors, specialized seal tight doors and caulking systems resist water infiltration. Concrete buildings also provide for less internal damage and easier cleanup if water and debris do enter.
Earthquake – Precast concrete buildings, including nonstructural components, can be designed and constructed to resist the effects of earthquake motions as prescribed by seismic mandated codes. Connections are designed between components to provide adequate strength to resist shears, axial forces and moments that permit rotational and/or translational movement without degradation of the buildings’ performance in accordance with ASCE 7. Standard and modified designs are available to accommodate all seismic zone categories.
Fire – Brush fires, electrical fires, lightning strikes, mishaps or arson all present fatal dangers to structures. Fire ratings of precast concrete can far exceed that of wood, metal or thin wall masonry. Concrete components can be designed to meet any degree of fire resistance that may generally be required by building codes, insurance companies, and other authorities. Fire resistance ratings of a building can be determined from ASTM E119 standard fire tests, code-approved empirical data, or by calculation procedures detailed in industry codes.
Vandalism – Vandals are a common problem for many facilities. Reinforced precast concrete panels resist damage through actual strength of material as well as a visual and psychological deterrent. Surfaces can be treated with anti-graffiti coatings for easier cleanup. Electrical conduit can be cast into the walls versus exposed on the interior walls or placed behind sheet rock. Standard and optional features like; electric time locks, heavy duty doors and frames, LEXAN polycarbonate windows, metal mirrors, vandal resistant/kick proof vents, stainless versus porcelain fixtures, and tamper proof hardware all add an extra level of security.
Ballistics – Precast concrete structures can provide greater protection from gun fire than typical metal, wood, brick or concrete block. In tests, a 3” reinforced precast concrete panel met UL 752, Level 5 (NIJ Level 3) protection. This standard test uses military full metal copper jacketed ammunition fired from a hunting rifle, such as the 308 Winchester or a military rifle with muzzle energy of 2519-3048 foot-pounds.
Heavy Usage – In many facilities wear and tear is the number one factor in limiting the useful life of a building. Restrooms made of all-concrete, including interior walls and partitions not only stand up to abuse, but are also easily repaired when damage does occur. Long-life epoxy paints that combat mold and abuse are typically applied to interior walls. Exterior walls are normally impregnated with stain that long outlasts typical building finishes. Stainless steel or powder coated hardware, fixtures and trim that resist wear and corrosion provide years of service.
Precast concrete structures handle the stresses of the above listed risk factors using several means. Roofs and floors are post-tensioned for added strength – mechanically stressed to 30,000lbs after assembly by using steel cables strung through conduit channels cast into the panels. This creates not only additional strength but also increased water tightness of the exposed surfaces. Larger roof sections can be pre-stressed while being made in the factory. Pre-stressing or post-tensioning removes a number of design limitations associated with conventional poured on site concrete, allowing for the building of roofs and floors with longer unsupported spans and capable of carrying heavier loads. This allows for designing and building lighter and thinner concrete structures without sacrificing strength, and creates durable roof systems that last for the life of the building.
Multi-sectional (modular) buildings are designed using sectional roof (and floor) slabs with longitudinal post-tensioning. After building installation, the roof joints are fully grouted and transverse post-tensioning is applied across all roof sections along the entire length of the building. In addition to creating characteristics of a monolithic slab system across all sections, the post-tensioning process increases the average compressive strength of the roof diaphragm controlling and counteracting shrinkage and flexural cracks.
Working through The Design Process – Many precast building companies offer multiple pre-engineered standard restroom options eliminating or reducing the need for architectural services. Standard designs can also be used as a starting point for customized projects. Several companies offer multiple options accommodating various added functions; concession stands, press boxes, locker rooms, showers, utility rooms, storage and more. Precast buildings offers flexibility in aesthetic design to match specific facility looks. Roofs can be cast to emulate finishes like cedar shake or metal seams. Wall panels that look like wood siding, brick or natural stone are common choices. Each surface can be stained or painted to match specific color schemes.
Factory Manufacturing versus Site-Built Construction – Factory manufacturing normally provides for higher quality standards, testing and controls than site-built options. Precast concrete buildings meet current IBC, ADA, ANSI & US Forest Service specs and guidelines (as required). Many precast manufacturers offer restrooms as turn-key projects, including site preparation, outfitting and installation allowing for fewer tradesmen and less disruptions at your facility.
Foundations – What kind of foundation will be needed? Prefabricated concrete buildings can be designed to utilize Slab-On-Ground foundations as described in the International Building Code. A typical precast concrete building utilizes a precast floor set over a prepared granular base material (typically 4” +), successfully addressing the means for distribution of the building loads to the subgrade without the need for a perimeter footing or foundation system. Post-Tensioned precast concrete slabs allow for a stronger, more efficient building slab/foundation system – less concrete and steel are needed for the same structural capacity and the slab stiffness is increased so that the slab is better able to resist bending caused by differential soil movements. Poured footers or slabs, knee walls or even basement foundations are available as options.
Outfitting – For ease of ordering and faster installation, factory built and outfitted buildings are an option to consider. Either single or double restrooms or modules for larger buildings are completely outfitted with plumbing, electrical wiring and fixtures in the factory and arrive on-site ready to be hooked up to utilities and put in service. One major consideration is plumbing. Options are available for both Flush (Electric, water and sewer utilities available) or Vault (dry or remote locations). Vault restrooms sit on top of concrete vaults (tanks) accessible through hatches for pump out services. Other optional items to consider are; lighting, occupancy sensors, heating, hand dryers, water fountains, emergency horn or strobes, water saver plumbing fixtures, and solar power.
The Need for Durability – How long do I want this building to last, generations? How much of a consideration should you give to the cost of ongoing maintenance and periodical renovation? All-precast buildings hold up for decades with little maintenance. There are no shingles, siding, wood structure, trim, or flooring to periodically replace. Factory poured precast concrete reaches a high strength of 5,000 psi or more vs. typical 1,000-5,000 psi masonry block or brick with 750-2400psi mortar joints. Inherently, concrete provides a durable and sustainable solution.
Your Return on Investment – Do you have a need for value? While prefabricated concrete buildings may have initial costs slightly higher than some metal or site-built masonry or wood buildings, the long–term savings in maintenance and replacement or renovation costs play a role. Return on Investment, upfront savings in less site preparation, speed of installation and project timelines, and user satisfaction should all be taken into account.
Chris Reese is the Senior Engineer for Easi-Set Worldwide. In his role he oversees the research and development of new technologies within the precast concrete products industry, and manages the production of a wide range of Easi-Set Building engineering projects across North America. Reese is a graduate of the Civil and Infrastructure engineering program at George Mason University.