Hanok are built of various different kinds of woods but nails are not used to join the materials. Instead, Hanok are connected by using other natural materials and methods. The joining and connecting methods also mirror yin and yang principles.
Ieum refers to the joining of two wooden materials side by side, and matchum refers to joining two pieces of wood perpendicularly or diagonally. Various joinery methods are used in traditional Korean construction, including dovetail joints, halving joints, locust joints, and splayed scarf joints. The dovetail joint, the most popularly used joinery technique in Korean houses, consists of a series of trapezoidal pins interlocking with similarly-shaped tails. The locust joint has the same interlocking mechanism as a dovetail joint, except for the fact that the pins used have a longer tip, in a shape indeed reminiscent of a locust.
Hanok are built much like wooden furniture, connecting pillars to crossbeams, and therefore, traditional Korean houses can be built using raw materials alone. The frame of the house is constructed using the dovetail method, joining pillars, purlins and crossbeams tightly and securely enough to be able to stand on its own. Other joinery techniques used in Korean houses include tongue and groove joint, formed by the insertion of the tongue of one intersecting wood piece into the groove of the other, and miter joint, in which two intersecting pieces of wood are joined at an angle, usually 45°, so that the intersecting ends are completely invisible.
The hardwood floors of a hanok kept the house cool and breezy during the hot summers and, due to the ondol system, warm and cozy during the cold winters. Ondol is a unique heating system native to Korea. It goes back to prehistoric times, when a furnace attached to the room transmitted heat to the floor through a stone substructure. An age-old, yet highly scientific system, ondol keep a room toasty warm. The fire, which is started at the agungi (fireplace), travels through the underground flue until it reaches the gaejari (pit that retains heat), and then once the heat cools off, soot particles sink to the bottom and clear white smoke is released through the chimney.
Ondol, the traditional heating system of Korea, consists of an agungi (fireplace), a gorae (heat duct) and a gulttuk (chimney). Gudeuljang (thin stone slabs) are placed over the heat duct that runs from one end of the room to the other, with the in-between space filled with dirt or rocks. The flat stone slabs (usually granite) are most often 5–8cm thick. The system is designed so that the hot smoke reaches all parts of the floor substructure so that the floor is heated evenly and warm in every part. The floor is slightly raised toward the side where the chimney is located. Meanwhile, the section of the floor, closest to the fireplace, can become extremely hot. To avoid injury, extra-thick stone slabs are placed in this area, usually in two layers. Thanks to the thickness of the stone slabs, this area of the floor tends to retain heat for many hours after the fire goes out in the fireplace; hence, the great heating efficiency of the ondol system.
1 Agungi (fireplace) 2 Bulmokdol (extra-thick stone slabs placed at the point of intersection between the agungi and gorae) 3 Gudeuljang (stone slabs placed above the gorae) 4 Gorae (heat duct) 5 Gulttuk (chimney)