On the shores of Lake Toba and on Samosir Island, old timber houses stand on posts beneath tall, curving saddle roofs, like boats turned upside down against the sky. To a passing visitor, these houses may seem little more than a charming backdrop for photographs. But for those willing to look longer, every part of the house holds a way of thinking about the cosmos, about relationships between people, and about how to endure on ground that occasionally trembles.
This essay takes apart the three-coloured carved gorga ornaments and the system of nail-free timber pegs, the two things most often discussed when people talk about the traditional Batak Toba house. We read them not as antiques but as working architecture: houses designed to be lived in, maintained, and passed down, and able to endure for centuries against volcanic earthquakes in a region shaped by an ancient eruption.
The House as a Map of the Cosmos
In many accounts, the Batak Toba understand the cosmos as three layered worlds: an upper world where the gods dwell, a middle world where humans live, and a lower world associated with the forces beneath the earth. These layers are often called banua ginjang, banua tonga, and banua toru. The traditional house, known as the ruma, repeats this arrangement in its vertical section.
The space beneath the floor becomes the lower world, the living space in the middle becomes the human world, and the soaring roof becomes the upper world. This division is not merely a symbol attached to the building; it also determines the function of each layer. What is stored, who lives where, and how people move inside the house all follow the same logic. In other words, the plan and section of the house are a cosmological diagram you can live in.
The same logic can be seen at the scale of the village. A traditional settlement, called a huta, usually arranges its houses in one or two rows facing each other, with a long courtyard in between. Across from the row of houses there often stand rice granaries, or sopo, which resemble houses but are more open at the bottom. This shared courtyard serves as a ceremonial space, a place to dry the harvest, and a place for children to play. Houses, granaries, and courtyard form a single spatial whole that shows how private and communal life support each other.
The Underfloor: A Lower World at Work
The floor of the house is raised well above the ground, carried on large timber posts. This underfloor space has traditionally been used for livestock, tools, or firewood. In practical terms, raising the floor protects the occupants from ground moisture, standing water, and animals. Air can flow beneath the floor, keeping the timber dry and slowing decay.
From the perspective of contemporary architecture, the underfloor is a clever answer to how a single structural decision can resolve several problems at once: climate, health, security, and the household economy. It also makes the house feel light, as if it does not press down on the earth but simply sits upon it.
The underfloor also serves as a transitional space. From there the occupants can watch over the courtyard, keep tools that are often used, and shelter from the rain without climbing into the house. In houses that no longer keep livestock, the underfloor is often turned into a place for weaving, a small workshop, or a family sitting area. This change of use shows how adaptable the basic design of the stilt house is in the face of changing times.
A Central Space Without Partitions
To enter the living space, people usually climb a ladder and pass through a fairly low door, so guests must bow their heads. Many writers interpret this bowing as a gesture of respect toward the host. Inside, the central space is wide open, with no permanent partition walls. Several related families may live together under one roof, each occupying a particular part agreed upon according to custom.
The absence of partitions does not mean an absence of boundaries. Boundaries are formed by social agreement, the position of the hearth, mats, and family belongings. The space becomes flexible: by day it is used for work and receiving guests, at night it becomes a sleeping place, and during ceremonies the entire floor can host a large gathering. For architects used to heavily partitioned plans, a space like this is a reminder that privacy and togetherness can be arranged through habit, not only through walls.
Light enters through small openings in the side walls and gaps beneath the roof. The interior tends to be dim, cool, and lightly smoky from the hearth. The smoke is not merely a side effect, since it is believed to help preserve the timber and the palm fibre of the roof from insects. Once again, a daily habit is directly linked to the life of the building.
The Soaring Roof
The roof is the most recognisable part of the Batak Toba house. It is a saddle shape with a curved ridge, its front and back projecting well beyond the walls, so that from the side its silhouette resembles a horse's saddle or a boat. Traditionally the roof is covered with ijuk, the black fibre of the sugar palm, which is waterproof and light enough for a timber structure.
Working with ijuk requires its own skill. Sheets of fibre are laid in layers, tied to a bamboo or timber frame, then compacted until thick enough to withstand heavy rain. A roof like this can last a long time if maintained, and damaged sections can be patched without replacing the whole covering. Ijuk also dampens the sound of rain, so the space below stays quiet even when the weather outside is bad.
The large volume of the roof creates space beneath the ridge. In many records, this space is used to store valuables and family heirlooms, in keeping with its position as the upper world. In terms of climate, the tall roof creates an air cavity that helps keep the living space below cool, while the long eaves protect the walls from rain and heat.
Gorga: Three Colours, Many Meanings
The front of the house is adorned with gorga, wood carvings coloured in three main hues: red, white, and black. These three colours are often associated with the three layered worlds and with the values of life, although interpretations can differ from one village to another. Traditionally, the pigments were made from natural materials such as earth, stone, and soot.
Gorga motifs are highly varied. There are tendrils and interlocking circles, there is the figure of a lizard often read as a symbol of adaptability, and there are breast forms associated with fertility and maternal love. At the front, the large-eyed face of the singa-singa is often read as the guardian of the house. All these motifs are arranged in fields that follow the layout of the boards, so ornament and construction are never truly separate.
Gorga is usually made by carvers who master inherited patterns. They do not simply copy, but adapt the composition to the size of the board, the standing of the house owner, and the message to be conveyed. The process of carving, colouring, and installing these boards can take a long time and is often accompanied by family deliberation. That is why gorga can be read like a document: it records the taste, skill, and values held by the family who lived in the house when it was built.
What interests graphic designers is the discipline of its composition. Gorga fills a surface with a dense yet orderly rhythm, uses strong colour contrast, and repeats the same module with small variations. This principle is similar to the way we build patterns or visual identity systems. The difference is that gorga is made with a chisel and endures in the open air, not on a screen.
In the Batak Toba house, ornament is not a final layer applied once the building is finished. It is the way the house speaks about who lives in it and how they see the world.
Pegs, Lashings, and Breathing Timber
The structure of the traditional Batak Toba house is assembled without nails. Beams and posts are connected with notched joints, timber pegs, and lashings. The main posts are not sunk into the ground but set on stone footings. This system makes the building flexible. When the ground shakes, the joints can shift slightly and absorb the forces instead of snapping like rigidly locked joints.
The Lake Toba area lies in a geologically active region, so this flexibility is no accident. Traditional carpenters may not have used the terminology of modern earthquake engineering, but experience handed down through generations taught them that a house that sways a little is more likely to survive than one that resists the shaking. This knowledge is stored in the details of the joints, the dimensions of the posts, and the way beams are fitted to lock into one another.
Nail-free joints also make maintenance easier. Decayed parts can be removed and replaced without dismantling the whole house. The timber chosen is usually a hardwood from the surrounding forest, patiently seasoned before use. This is where vernacular architecture reveals its intelligence: it is designed not to last forever untouched, but to be continually cared for by the community that inhabits it.
Building a house was never the affair of a single family. In many records, raising a house involved relatives and neighbours, from felling the timber and hauling the posts to lifting the roof frame. This shared labour kept construction knowledge passing from hand to hand. Young people learned by holding the ropes and carving the pegs, not from technical drawings. When the tradition of mutual help weakens, what is lost is not only labour but also the way that knowledge is passed down.
Reading Measured Drawings
Documenting a traditional house in the form of architectural measured drawings is work that demands patience. Surveyors must climb, crawl through the underfloor, and record every joint carefully. Yet the results are invaluable. Plans, elevations, and sections reveal what photographs miss: the relationships between beams, the pitch of the roof, the floor heights, and the proportions repeated throughout the building.
When measured drawings are placed beside documentation of the ornaments, it becomes clear that the size of the gorga, the position of the posts, and the span of the roof are all related. The house was designed as a single, complete system. For architecture students, reading drawings like these is an exercise in understanding a building from the inside, not merely admiring its outward form.
There are a few things we usually look for when reading measured drawings of a vernacular house:
- How the load of the roof is carried down to the stone footings.
- Where the joints are designed to move, and where they must stay rigid.
- How floor height and the placement of openings affect airflow.
- How the ornaments follow the edges of the boards and structural beams.
Lessons for Today's Architects
Admiring a traditional house is not the same as imitating it. Attaching a curved roof to a concrete building does not automatically make it contextual. The more useful lessons lie in principles: raising the floor for the health of the building, designing joints that can be maintained, using local materials, and making room for communal life.
These principles are relevant to Indonesian cities facing heat, heavy rain, and earthquake risk. Architects can translate them with the materials and technology of today while still honouring where the ideas came from. Working with carpenters and customary communities matters too, because they hold knowledge that is not written in textbooks.
There is also a lesson about scale. The Batak Toba house was not designed merely to impress from afar, but to be lived in comfortably by the human body: the height of the ladder, the width of the openings, and the position of the hearth follow everyday habits. Buildings today, often oversized and uniform, frequently lose this kind of sensitivity. Paying attention again to the relationship between body, habit, and space is a simple step that can begin with any home.
Caring for What Still Stands
Many traditional houses now face serious challenges. Ijuk is increasingly hard to obtain, so roofs are replaced with corrugated zinc, which is hotter and noisier. Large timber is no longer easy to find, and many young people have moved away to work. Some houses are well cared for by families and communities, while others are slowly abandoned. The most successful conservation efforts usually place the residents in the leading role, rather than treating their homes as a mere tourist attraction.
Tourism can be both an opportunity and a threat. On the one hand, visitors open up a source of income that helps families maintain their houses. On the other, the pressure to look attractive can encourage renovations that ignore original materials and techniques, or turn a house into a stage without life. A balance between the two can only be found when the community itself sets the direction, supported by the knowledge of architects, researchers, and local government.
Documentation, whether in the form of measured drawings, photographs, or oral records, becomes a bridge so that this knowledge is not lost. It allows the next generation to rebuild, repair, or at least understand what once existed. In this sense, a book about traditional houses is not just reading material, but part of the work of care.
For readers who wish to explore more deeply the measured drawings, ornaments, and cosmology of the timber stilt houses on the shores of Lake Toba, the monograph Arsitektur Rumah Tradisional Batak Toba presents complete architectural documentation, from the details of the gorga to the structural system, and deserves a place on the desk of every spatial designer.
