The design width of an expansion joint at an average air temperature is referred to as the nominal joint size. The first step is to acknowledge the nominal joint size for a particular building and the range of movement between the fully contracted size and the fully expanded size. The building movement that makes expansion joints necessary occurs due to several common reasons with three types of movement that typically need to be accommodated:

• Thermal Forces: This type of movement is most typical and caused by daily environmental temperature changes in and around the structure. Thermal movement is primarily “one-directional” in nature and is the result of the expansion and contraction of structural elements as affected by heat, cold, and humidity levels. The typical amount of thermal movement is approximately 10-25 percent of the nominal joint size. That means the minimum contracted size (i.e., during cold temperatures) should be 10- 25 percent more than the nominal joint size and the maximum expanded size (during warm temperatures) should be 10-25 percent less than the nominal joint size. If expansion joints aren’t put in, then thermal expansion and contraction can cause buckling of structural surfaces in places like roofs and interior floors.
• Seismic Activity: The shifting of the earth’s tectonic plates (i.e., earthquakes, tremors, etc.) and shifts along fault lines are the source of seismic activity. Seismic movement may be horizontal, vertical, in shear, or a combination of all three. Seismic expansion joint widths may need to increase with higher floor levels to accommodate the additional, cumulative movement that needs to be addressed. These joints must have the capacity for movement of plus or minus 50-100 percent of the nominal joint size associated with them. When it comes to expansion joint systems, it is important to select systems that can “reset” themselves after a minor seismic event and allow workers to reposition panels easily.
• Wind: loads Movement induced by high winds, can force the structure to sway. This movement is normally perpendicular and/or parallel to the joint. This is common where a low horizontal building span meets with a taller vertical element. Movement in these joints is typically on the order of 50 percent. Over time, the near-constant effects of wind pressure on the sides of buildings can lead to serious issues, such as aerodynamic instability, torsion or swaying, erosion of certain building materials, and cladding failure due to wind load or impact of debris. In extreme cases, it can lead to structural failure and damage to people and property. Therefore, when designing a structure, it must be able to both withstand high wind loads, but also work with them. As with seismic activity, expansion joint systems should be able to “flex” and yet remain in place as the building sways or torques.

By properly addressing all these conditions, the building can be protected from movement that will invariably occur and avoid the resulting damage that is possible.

Typically, the joints need to run continuously through all adjacent planes to fully separate building sections and allow independent movement. That means that any given project scope could include interior joints, exterior joints, or both, in things like walls, roofs, floors, building veneers, soffits, parking decks, patios, roofing systems, etc.

Commercial Washroom Systems, ADA Compliant

One of the most used parts of your school are the bathrooms. The level of resiliency and cleaning product durability that can withstand commercial bathroom or washroom environment needs to be high. At the same time, education systems must consider not only the durability of these spaces, but also ADA compliancy. When it comes to shared dormitory washrooms, we see a few common problems: wall panel cracking, waterproofing membranes, and showers that are not ADA-compliant.

Be sure to call out silicone joints as needed to ensure panels can expand and contract with the structure. Typically, these can be placed at inside corners, but may need to be done between in-line panels depending on anticipated temperature fluctuation in the room. Well-written installation instructions should call out how often these are required

Waterproofing membranes in showers and bathrooms have been an industry standard for decades. But the challenge is making sure drainage holes cut into the membrane perfectly align with the stub up and tie into the drain hardware securely to prevent leaks. However, membranes are not needed with Inpro shower bases, but can be used if the membrane is compatible with silicone per membrane manufacturer’s recommendations. Modifications may also be made to the cast base drain opening to allow for a drain assembly that can accommodate a membrane. This added layer may disrupt sizing and will need to be accounted for on a job-to-job basis. There is the potential to save time on the jobsite and shave dollars off the budget by omitting membranes, when possible, when a manufacturing offers a non-porous solid surface designed to be water-tight when the proper sealants are used.

When it comes to ADA compliancy, templates are a great option for showers. use them for precise Transfer or Alternate Roll-in showers to ensure the studs are adequately spaced to ensure 36" (914mm) inside dimensions. When possible, take advantage of ADA minimums – such as 60" wide Alternate and Roll-in showers; 30" (762mm) depth for Roll-ins; and 36" (914mm) opening for Alternate Roll-ins. In other words, they are minimums, and by stretching the dimension a bit vs. calling out exact dimensions you can account for construction and manufacturing tolerances. Oversizing by even .25" (6.4mm) can be very helpful. Remember that the transition from floor to base must not exceed .5" (13 mm). It is critical to understand the height of the product specified and the recess or float needed to facilitate an ADA- compliant washroom. For example, a rear trench drain may be over 2x as thick at the front edge vs. a front trench drain design.

Working with a manufacturing that is well versed in commercial washroom systems can help you avoid common mistakes, and ensure your washrooms meet codes and standards that exceed expectations.

EXPANSION JOINT SYSTEMS

Once the engineer has determined the locations and recognizing that an open joint in a building needs to be addressed, it is then typically up to the architect to select the means to cover or seal that joint. Any expansion joint filler or cover system needs to accommodate the full anticipated range of movement. When properly designed and constructed, they can be integrated with their surrounding construction such that they blend in with a design and almost disappear. Common ways to do that depend on the size of the joint. Caulking or sealant may be all that’s necessary for very narrow joints, but wider joints need a coordinated system. Compressible fillers are common and made from different types of foam that is secured into the joint. Others use bellows or blankets to fill the gap that can bend and move with the adjacent building structure. Architectural joint cover systems are also common and can be selected based on their ability to absorb building movement, support a given load, maintain safe egress where applicable, and be compatible with adjacent surface finishes.

In light of all of the above, we take a closer look at some different types of expansion joint systems in the following sections.

Fire-Resistive Joint Systems

In many cases, expansion joints are installed in construction that needs to maintain a fire-resistive rating. This is problematic since building expansion joints in floors, roofs, or walls create a pathway for fire and smoke to travel through. Of particular concern is the need for expansion joints in dormitory buildings at boarding schools or on college campuses, where fire isolation and containment is mandated by codes for occupant safety. The way to address such fire concerns is to use expansion joint fire-barrier products or systems that can provide protection for 2, 3, or 4-hour rated conditions as warranted. That means the joint products or systems need to be fire-resistance-rated in accordance with normal test and fire rating standards. When installed, the intent is to provide a continuous, uninterrupted fire barrier in the structure and the joints─all of which is critical for life safety. Recognizing this safety issue, an expansion joint system can be selected to fit the specific needs of a project and provide the level of protection required to keep the threat of fire contained.

There are two fundamental types of fire-rated joint systems. The first is to use compressible foam products that have been shown to achieve appropriate fire ratings. In some cases, the foam can be totally impregnated with fire retardant as an integral part of a manufactured product. This is the best solution and type of fire-resistive product to specify. A fire-rated pre-compressed foam material that is totally impregnated with fire retardant will maintain the specified and tested fire-rated assembly even if the facing has been damaged. Alternatively, a field application of an intumescent coating or silicone can be applied on the face of the foam joint. This method is, indeed, cheaper for the manufacturer. However, seals that rely on their silicone or intumescent face coating will no longer achieve their UL-2079 assembly rating if either of these faces are damaged or vandalized.

Another fire-resistive product is based on the use of fire blankets. These are the most versatile system, suitable for expansion joint gaps of 2-32 inches and able to withstand high rates of movement. Fire blanket systems come in two forms—either ceramic cloths with intumescent layering or graphite sheet goods encasing insulating blankets. In seismic conditions, they allow for approximately 50 percent of joint compression and expansion movement. Some models are able to retain their rating throughout lateral shear movement testing while others cannot. Fire blankets are tested in concrete, but alternate substrate conditions may also be acceptable.

Note that fire blankets can be specified either to withstand water or not. Those that cannot withstand water exposure and become wet are often rendered useless against smoke, fire, and heat; even after redrying, they carry diminished fire resistance. Products that are rated and tested for water exposure during or after construction, or for open structures such as parking facilities and stadiums, provide fire protection even if they become wet. It is important, therefore, to select and specify the appropriate material for the water conditions anticipated in the building.

Foam Seals

In certain applications, the use of foam seals in expansion joints provides a solid seal against the elements and moisture protection. Foams can also provide acoustic and insulation properties. As a general rule of thumb, limiting foam seals to applications with a joint width of no more than 8 inches (200mm) or smaller is good practice. Use of foams for expansion joints larger than 8 inches leads to two things: 1) exceeding the foam’s performance characteristics, including possible sagging of the foam seals in vertical applications due the weight of wider sizes; 2) exponentially higher costs compared to other expansion joint cover solutions.

Fire-rated foam seals are also available and suitable for 6-inch and smaller gaps and conditions where abuse is not likely. These systems are comprised of open-cell polyurethane foam impregnated with a fire-retardant material. These foams can be faced with colored silicone to match a desired décor or design aesthetic. Fire-rated foams are usually lab tested in concrete and cement-board wall conditions (not drywall).

When selecting an appropriately sized foam, there are two fundamental types to consider: open-cell or closed-cell foam seals. Open-cell foams provide some breathability and allow for flow-through of water and vapor, making them best suited for vertical applications. Like many exterior veneer systems, if moisture becomes trapped in a wall cavity, building systems allow the moisture to wick out. This is a good quality and a major focus to eliminate potential mold issues in vertical applications.

By comparison, closed cell foams are absolutely watertight and do not allow moisture or bulk water to enter the body of the foam. They are best suited to horizontal applications where moisture could remain trapped and water penetration cannot be allowed. Closed cell can also be utilized on below-grade vertical applications as support and closure to positive-side waterproofing at expansion joints. These are tougher to compress but can be placed under tension (or expand) well.

Compression Seal Systems

As their name implies, compression seal joint systems are installed into a joint, absorbing movement and flexing through compression of the seal. This type is an excellent option for exterior application where waterproofing is required. These seals are best employed for heavy pedestrian and moderate vehicle loading such as plazas, decks, parking garages, etc. Nominal joint sizes for these systems should be in the 1-to-4-inch maximum range. Compression seal systems come in a few common forms: vehicular “winged” seals or the more moderate epoxied standard seals. Proper use of two-part epoxies ensures solid adhesion to the deck, and heat-welded seams ensure watertight performance. Building aesthetics can be enhanced using colored compression seals.

Roof Bellows Systems

Expansion joints that pass along a roof membrane need particular attention to remain watertight. Such systems use either a TPO or PVC membrane that is bowed up like a bellows so that it flexes to accommodate seismic or thermal movement. As with counterflashing, the seal must run under the metal flanges of the bellows system to allow water to be shed away from the joint opening. Also, a compatible, nonreacting mastic should be used to ensure watertight adhesion of the seal.

Beyond the typical horizontal aspect of a roof bellows expansion joint system, the transition to walls, parapets, edges, or other building components is critical. Tying in horizontal and vertical joint systems requires transition covers to help maintain watertightness. Architectural drawings and details should always cover this, but the reality is that sometimes transition covers and tie-ins are missed. This can cause significant problems in the watertightness of the roof and adjacent areas.

Metal Cover Plate Systems

In many cases, exposed foam or compressible seals will work just fine and provide suitable aesthetics for the particular area of the building in which they are installed. Often, however, there are cases where a metal system is called for in order to achieve the strength and durability needed. Metal cover plate systems should always be used for joints 6 inches or wider in open structures. Wider joints have surfaces that are exposed to direct loads imposed by tires. A system with shallow, thick, heavy-duty frames offers a high degree of strength in its profile for longevity against the constant vibrations imposed on the cover plates each time vehicle travels over it. Other attributes to look for include noise dampening and water resistance.

There are two basic types of expansion joint cover solutions in general–surface or recessed mounts. Surface mounted systems typically are very cost effective but have wider metal sections that are visible. They are simple to install and are great for remodels and additions or projects with particularly tight budgets. Products that are recessed into the deck are flush with the finished flooring and receive no jarring impacts from rolling loads. They also typically have far greater visual appeal since they can be specified with a recessed pan in the middle that can receive a finish material to match the adjacent materials (i.e., flooring, wall material, ceiling, etc.) In this way, the aesthetics of the space are not disrupted by looking at aluminum plates, however they do require greater trade coordination and are more costly. Nonetheless, they may be the best choice, particularly for interior or exterior systems that are subjected to a lot of pedestrian or light vehicular traffic as noted earlier.

CONCLUSION

Educational buildings serve large numbers of people with different needs. That use makes them inherently subject to conditions that require greater durability, safety, and performance. Addressing specific design items such as wall protection, elevator cabs, window coverings, architectural signage, and expansion joints helps achieve overall building designs that can best protect the building and the people that use them.

Peter J. Arsenault, FAIA, NCARB, LEED AP is a nationally known architect and a prolific author advancing positive acoustical experiences through better building design. www.pjaarch.com, www.linkedin.com/in/pjaarch