This stainless steel movement profile allows horizontal movement via a tongue-and-groove connection. Photo courtesy of Schluter Systems.

This is an anodized aluminum, cove-shaped profile for inside wall corners, countertop/backsplash transitions, and floor/wall transitions that is ideal in environments with strict hygienic requirements. Photo courtesy of Schluter Systems.
It seems that no matter how hard we try to drive home the message, restrained movement of tile installations is a continued problem and regular mode of failure. Tile moves, wood moves, metal moves, it all moves; you can count on it. So, why not plan for it? Today's structures are much more engineered than in the past. Wood structures in particular have become highly engineered. They often employ many various types of engineered joists and engineered panels that are not fully understood by those installing them. The movement issue is further compounded by the tendency to build structures to minmum code requirements. Add a little fast track construction to the equation, like installing floors with temporay heat or just as the painter is finishing the walls the drywaller installed and taped last week that were barely dry, and you have a lot of moisture-induced movement in the structure. That is just about the time they call for the tile installer. So now we have the structure contracting while drying out and taking our tile job with it. Granted, this is a worst-case senario, but it is one installers see all the time.

This is a stainless steel, cove-shaped profile for inside wall corners or floor/wall transitions with strict hygienic requirements. Photo courtesy of Schluter Systems.
Expansion joints, also known as movement accommodation joints, are intentional interruptions in the hard materials making up a tile installation that provide enough space for the materials to expand and contract naturally without causing damage to either the tile installation or the surrounding structure. Today, most of the emphasis on expansion joints is placed on large commercial installations because they are required under the specifications that are part of a contract. But, the fact is, even small residential floors need, at the very least, an expansion joint around the perimeter of the floor. Current study shows that in today's modern minimum code compliant construction, as opposed to over-engineered structures in the past, they play an ever-increasing role of importance. The 2005 edition of the TCNA Handbook has made several changes to reflect the latest recommendations of the wood and concrete industry. Accepted industry standards recommend that expansion joints be placed:

The term expansion joint may have several definitions. One would be a separation provided between adjoining parts of a structure to allow movement where expansion is likely to exceed contraction. It could also be a separation between pavement slabs on-grade, filled with a compressible filler material or an isolation joint intended to allow independent movement between adjoining parts.
1. Wherever there is a change in the backing materials (e.g. a plywood subfloor meeting a concrete slab), or where tile work meets or abuts perimeter walls, curbs, columns, pipes, other penetrations or restraining surfaces.
2. Wherever tile work passes over control, expansion, seismic, cold, construction or other structural joints.
3. Every 20 to 25 feet in both directions for interior tile work not exposed to moisture or direct sunlight.
4. Every 8 to 12 feet to interior tile exposed to direct sunlight or moisture.
5. Every 8 to 12 feet in both directions for exterior tile work.

The term expansion joint may have several definitions. One would be a separation provided between adjoining parts of a structure to allow movement where expansion is likely to exceed contraction. It could also be a separation between pavement slabs on-grade, filled with a compressible filler material or an isolation joint intended to allow independent movement between adjoining parts.
The width of a movement joint varies too, depending upon its interior or exterior location and the temperature differences between summer and winter; interior tile work exposed to direct sunlight should always be treated as exterior. Manufacturers of tile and setting materials, The American National Standards for Ceramic Tile Installation and the Tile Council of North America TCNA Handbook recommend minimum widths must be increased 1/16-inch for each 15°F for the actual temperature range greater than 100°F between summer high and winter low. Minimum widths are as follows:

A construction joint is where two successive placements of concrete meet. In some cases it may be desirable to achieve bond and reinforcement may be continuous.
Exterior tile work
a. 3/8 inch minimum for joints 12 feet on center.
a. 1/2 inch minimum for joints 16 feet on center.
Interior tile work
a. For quarry, porcelain and all other floor tile, same as grout joint but not less than 1/4 inch.
b. For glazed wall or ceramic mosaic tile, 1/4 inch is preferred but not less than 1/8 inch.
Anyone doing tile work should be familiar with the contents of the TCNA Handbook. If not, you can contact the Tile Council of North America for a copy of the newly revised 2005 edition. It is relatively easy to use but upon opening it for the first time, you may find its contents a bit overwhelming. The following is a list of the most common floor locations for installing movement joints:

An isolation joint is a separation between adjoining parts of a concrete structure, usually on a vertical plane at a designated location so as to interfere least with performance of the structure. It is designed to allow relative movement in three directions and avoid formation of cracks elsewhere in the concrete and through which all or part of the bonded reinforcement is interrupted.
Floors: On all floor tile installations, there must be a perimeter joint between the last row tile and the enclosing walls. The joint should be a minimum of 1/4 inch and free of any grout, setting material or debris. As with all underlayments, if a backer board abuts the wall it to should have a 1/4-inch gap. There should also be joints located in the center of doorways where tile runs continuously such as a kitchen to a dining room or where an indiviual room changes direction such as an "L" shape.

Different Substrates: When the floor is composed of two different materials such as a concrete slab used to extend an existing wood subfloor, an expansion joint located directly at the split is required to accommodate the different rates of expansion and contraction. Two different materials have two different rates of movement. There is not a single membrane manufacturer who would warrant use of their product in such an application. This holds true for wood construction additions to existing wood structures. Neither backer board nor plywood over the new framing will stop the movement on the new addition.

A contraction joint, also known as a control joint, is formed, sawed, or tooled groove in a concrete structure to create a weakened plane and regulate the location of cracking resulting from the dimensional change of different parts of the structure.
Columns and Beams: On concrete structures, floor tile installations should always be isolated with an expansion joint particularly around columns. Columns and column pads perform a supporting function independent of the floor and must be allowed to move. In wood structures, the tile directly over a beam is solidly supported where the material placed on either side of the beam will deflect a certain degree till it reaches the next area of support. Ideally a joint should be placed over the center of the beam.

Concrete Floors: Concrete floor slabs may be produced with cold joints, control joints or expansion joints. Cold joints are cracks that appear when fresh concrete is placed next to an existing slab. Control joints are partial interruptions in a slab that are intentionally placed to direct or channel cracks that will appear either during or after the slab has cured. Control joints can be formed or molded while the concrete is still plastic, or they can be saw-cut after the concrete has sufficiently hardened. Concrete slab expansion joints are produced when two neighboring slabs are separated by a filler strip placed before the concrete is poured. The joints are designed to allow for independent movement of each slab. These "joints" are usually found on commercial installations but they may also be found on residential construction. If tiles are to be applied on these slabs, an expansion joint must be incorporated into the tile portion and must be located directly above the joint in the concrete. They may not be relocated with a membrane.

Perimeter Joint
Making Expansion or Movement Joints
The right time to discuss the need for joints is at the planning stage so that all other trades involved with the tile installation (concrete or carpentry crews) know precisely where the joints will be located. This means working with the owner, architect or general contractor to ensure that everyone agrees on the location for all construction joints. Constructing field made joints that perform is no easy task. They require a fair amount of skill and can be very time consuming. Pre-made joints can become very desirable for this reason and you will find in many instances they are less costly. A movement joint is an open slot that extends from the top of the tile. A compressible filler, backer rod, or bond breaker tape is often used to prevent three-side bonding, depending on specific application. This is followed by a bead of sealant or caulk. A movement joint located around the perimeter of a floor tile installation is the easiest to make. You simply hold the tiles at least 1/4 inch away from the wall and apply caulk or sealant if needed. Usually the perimeter of the floor is then finished with a baseboard of tile, wood or other material that masks the expansion joint. If not the customer should be made aware that the joints will not resemble a grout joint. For control joints, the layout of the tiles must place the grout joint directly above any construction joints. As this is rarely practical, a membrane is often used to relocate the positioning of the joint. If a membrane is employed, some will allow for relocation of all but true expansion joints to the next full grout joint. Visible joints ideally should mimic the appearance of the grouted joints so they do not detract from the appearance of the finished installation. To make these joints function properly, they need another element called backer rod. Backer rod has a round cross-section, is available on spools and is placed snuggly in the joint to the recommended depth. This prevents the joint from destroying itself when it opens or is compressed by providing only two-sided adhesion. Backer rod is hard to find in stores, but easy to find on the Web. Because it can make the difference between a joint that lasts and one that fails, it is worth searching for.

Choosing and Installing the Caulk or Sealant
Sometimes a compromise has to be made when selecting a material to place in the movement joint. As this critical part of every tile installation is often ignored, there is not an overwhelming choice of color when it comes to sealants. Sealants typically have a short shelf life and are three to four times the cost of regular caulks. Caulk is an all-purpose term and often used to describe sealants. Most often the terms are used interchangeably, and the products serve the same purpose: to fill gaps and allow movement between building materials while keeping water and soil at bay. Many times the approach taken is to select durable sealants for heavy-duty service applications. Silicone stands up to extremes of moisture and temperature, cures soft, and remains flexible. Silicone is inorganic, it is unaffected by UV radiation and many resist mold and mildew. Silicone can be applied at virtually any temperature and can stand up to adverse conditions shortly after application. Polyurethanes sealants can stand up to abrasion and remain flexible and weather resistant. For regular duty installations (residential applications), you often must sacrifice durability for invisibility and select a sealant or caulk that closely matches the grout joint. Water-cleanable caulks are available to match most grout colors (some are even available sanded to match the texture of grout) These may require more frequent replacement than the other types, but are worth the additional effort and expense if seamless good looks are important.

Generic Movement Joint
To use water based caulks, you simply fill the joint with caulk and then compress it into the joint with a striking tool dipped in water (you may have to clean and re-wet the strike as you go. Clean the excess with a sponge, making several passes until the excess has been removed. It is a good idea to check the caulk joint area to ensure that all the excess has been removed. Applying silicones and urethanes are a bit more challenging. You should really tape the sides of the joint to protect surrounding areas from residue, it makes clean up much easier. When tooling silicones or urethanes, a little soapy water will keep caulk from sticking to the tool used to finish the joint. Remove the tape by pulling it over the top of the joint and protect the area until the caulk has cured. Time will vary with product; some take hours, some days. Whatever brand of sealant or caulk you use, follow all manufacturers instructions regarding preparation of the slot, backing, application temperature and humidity, and curing requirements.

When properly made and finished, movement joints provide service for many years. However, because expansion joints move and flex and get abraded and torn, they will eventually wear out. Sometimes, the entire system of joints may need replacement while at other times, only a spot repair is needed. It is wise to make the owner aware that replacement or repair is a maintenance item, not a failure. I would also like to acknowledge I understand the difference between real world and perfect world. In the perfect world, every job would have joints as needed using proper materials. In the real world, there is nothing harder than selling a caulk joint down the middle of someone's dream floor. Likewise, most are very adverse to having joints in doorways or leaving the perimeter of the room with a 1/4-inch gap. All I can say is at that point it becomes a business decision. That the floor is going to move for any number of reasons is a given. Not putting the joints in is a risk. Many get by for numerous years and never have a problem; others are not so fortunate. You make the call.