air to dry naturally. The timbers may be stacked with spacers (known as "stickers") between them. This process allows the moisture content of the logs to naturally fall as the timber dries. In areas of high humidity, it may require as much as one year per inch of log thickness to dry. Arid climates may require less. A log with a diameter of 8 inches will usually reach equilibrium in about 18 months in the Rocky Mountains of North America. Air circulation is critical or the logs may begin to rot before properly drying, especially in humid regions. If the logs are to be dried to equilibrium with the local climate the process may take several years, depending on the location and size of the timbers. In some environments, the logs must be kept under some type of roof or cover to reduce the impact of rain storms on the drying process. Once the logs have dried for the desired length of time, they are profiled prior to shipping. Profiling usually does not take place until shortly before shipment, to ensure that the logs stay as uniform as possible. It is uncertain whether this process is advantageous; it depends on many factors such as local climate, wood species, its size, and the location of the log structure. Kiln-dried logs Mills that have a kiln on site have the option of artificially accelerating the drying process. Green timber is placed inside a large oven, where heat removes moisture from them; however, they can suffer severe checking and cracking if the kiln controls are not properly monitored during the drying process. Use of a kiln can reduce the drying time from many months to several weeks. Kiln-drying usually results in an average moisture content of 18-20% ("average" means the average moisture content of the outside and the center of the log). In North America, logs reach equilibrium moisture content at about 6% and 12%; since most kiln-dried logs are dried down to about 18% to 20% moisture content, kiln-dried logs can be expected to shrink and settle over time, but to a lesser extent than green logs. Glue-laminated timber "Laminated" or "engineered" logs are a different approach to log-house building. Full trees or (alternatively) sawn cants (unfinished logs to be further processed) are brought to a mill with a dry kiln, the bark is removed and the trees are sawn into boards