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Why do rooms with more sunlight need more movement joints?
The intent of the guideline regarding sun exposure is to recognize that areas that get warm (or wet) may experience greater amounts of differential expansion. If the areas exposed to sunlight are warmer than surrounding areas, movement joints should be used more frequently. If the tile surface is not appreciably affected, no accommodation is needed in the joint spacing.
Only the area subjected to increased temperature needs to have movement joints more closely placed, not the entire floor if elsewhere the floor is an even temperature.
What other things should be considered when determining spacing for movement joints?
Many things can subject the tile layer to shear forces in addition to temperature and moisture. The following is a partial list:
- Continued curing of the concrete substrate can put the tile in compression
- Deflection and vibration of the substrate – particularly with suspended slabs
- Seismic activity
- Changes in the plane of the substrate
- Location of weight-bearing columns
- Type of tile or glass