than handcrafted houses. There are about 500 companies in North America which build the handcrafted, scribe-fit type of log house. Components The logs in log houses have a varying degree of moisture content; all logs have moisture when freshly cut. In the case of handcrafted logs moisture will naturally leave the timber, drying it out until it stabilizes with its climate. This drying-out causes movement and shrinking of the log's diameter. As logs and timbers dry, the differential shrinkage (radial versus tangential) causes small cracks (known as "checks") to open slowly over time. Checking is a natural process in both air- and kiln-dried logs. This occurs in all log houses regardless of construction method or how the timber is allowed to dry, and is considered normal. Milled logs are processed in a different manner from handcrafted logs. Logs destined to become milled logs may become one of several types, depending on the desired quality and results. Green logs Logs that are cut from the butt forest, brought to a mill or to a log-house construction yard, have their bark removed and are used to build a log-house shell (handcrafted log houses), or sent through profiling machines (manufactured logs) are usually referred to as "green" logs if they have not been air- or kiln-dried. "Green" does not refer to color, but to moisture content. The actual moisture content of "green" logs varies considerably with tree species, the season in which it was cut, and whether sapwood or heartwood is being measured. Green logs may have a moisture content ranging from about 20% to 90%. One type of air-dried log is "dead standing," which refers to trees which have died from natural causes (bug kill, virus, fire etc.) and cut down after they died. Standing dead trees may be cut one month or several decades after they died, so the term "dead standing" does not necessarily mean the logs have dried down to equilibrium moisture content. Dead standing logs can be green, or more-or-less dry. After construction, green logs dry in service in the log building. Within about four years, green logs which are part of a completed log house reach equilibrium with local conditions and have an equilibrium moisture content of between 6% and 12%, which varies by local climate, season and location. Air-dried logs Some log home companies let the fresh-cut logs (or milled timbers) sit outside in the open