Batak Toba culture centres on Lake Toba and the sacred island of Samosir that lies within it. Jabu is the Toba language word for rumah adat. The houses are made up of three sections. A substructure of large wooden pillars resting on flat stones (or concrete nowadays) protects the structure from rising damp. Some of these pillars support longitudinal beams known as labe-labe, which run the length of the house at head height to carry the massive roof. Other pillars carry two large beams with carved singa heads which, with two lateral beams mortised into them, form a great ring beam bearing the small living area. The substructure is strengthened by beams mortised into the piles which double as night stalls for cattle. Walls are lightweight and lean outwards and provide additional stability to the structure. The wall and the wall plate supporting the rafters hang from the labe-labe with rattan cord, while the base of the wall sits on the ring beam. The rafters spring from the wall plate and are angled outwards producing the roof curve. In lieu of horizontal bracing battens, diagonal ties—running from the middle of the labe-labe to the gable ends—provide reinforcement.[2]
The large steeply-pitched saddle back roof dominates the structure. The roofs are traditionally thatched, and with no internal roof trusses they provide a large internal space. Sharply projected triangular eaves and gables overlap all around the substructure. The front gable extends further than the rear gable and is finely carved and painted with motifs of suns, starts, cockerels, and geometric motifs in red, white, and black. The rear gable remains plain.[2]
Toba Batak extended family alongside their intricately carved jabu house. c. 1900
The living area, which is supported by lateral and transverse beams, is small and dark. Light enters through a small window in each of the four sides. The inhabitants spend most of their time outdoors and the house is largely used for sleeping. An attic space is provided by a flat wooden ceiling over the front third of the living area. Family heirlooms and sometimes shrines are stored here. Traditionally, the Toba Batak would cook over a hearth at the front of the living room making the living area smoky. With recent changes in hygiene practises, the kitchen is now often in an extension at the rear of the house.[2]
The original Toba Batak houses were large communal houses, but these have now become rare, with most houses now built in the ethnic Malay style with both modern and traditional materials. While more spacious, better ventilated, brighter, and cheaper to build, the jabu is considered more prestigious. Where jabu are still lived, they are generally smaller single-family dwellings. Whereas previous versions of the jabu were accessed through a trap door concealing steps in the floor, times are now less dangerous and more convenient wooden ladders at the front of the house provide access.[2]
Toba Batak rice barns (sopo) were built in a similar style but are smaller than the jabu. Rice was stored within the roof and was supported by six large wooden pillars, which carried large wooden discs to prevent rodent ingress. The open platform beneath the roof structure was used as a working and general storage space and as a sleeping place for guests and unmarried men. Rice barns are now rarely used for grain storage, and many have been converted to living areas by walling off the open-air section between the sub-structure and the roof, and adding a door