Spacing is a key consideration when it comes to joists. Joists that are spaced close together provide a strong framework for floors and have high weight-bearing potential. However, joists that are spaced as far as 2-feet or more apart are much less expensive to install when constructing a house, but provide significantly less support. If joists are spaced too far apart, they will fail over time due to the stress from a floor or ceiling.
Joists need to be installed correctly in order to work properly. If the weight of a house is especially heavy in one area due to masonry or improper load bearing, there is a higher probability that joists will eventually fail. Cutting into or through joists for basement or attic projects can also lead to joist failure due to uneven loads on the building's structure.
Moisture is generally deleterious to wood construction. This is especially true of wood joists, which play such an important supportive role in house construction. If joists are constantly exposed to moisture, which is especially likely underneath manufactured homes, they can start to rot and sag. This can lead to failure, creating a series of structural problems in addition to potential health hazards if mold proliferates.
Pests can do irreparable damage to the structure of a home, especially if it is made of wood. Joists are susceptible to termite damage, which can quickly lead to failure and requiring expensive repair. Proper insulation and good air flow through vents can help prevent pest problems.