Fundamentally, the roof offers shelter against precipitations, extremes of the sun, and strong wind. Together as a response to the Earth’s varying weather and climatic conditions, different cultures from different geographical points of the globe have developed a variety of unique roofing designs that are suitable for each of their respective climates. In tropical regions specifically, due to the high chances of heavy rainstorms, roofs are typically found to have dramatically steep slopes. This feature can effectively help with quick rainwater runoffs, preventing homes from water damages.
Khmer roofs share a lot of similarities with those of its neighboring Southeast Asian cultures. However, there are still some easily distinguishable aspects that help set traditional Khmer roofs apart from those of our neighbors — especially in terms of their design.
As the decades progress, we can start to clearly get a sense of how global cultural exchange has played a vital role in the evolution of roofing in Cambodia. Newly developed technologies and techniques have been slowly eliminating the concerns and constraints once used to be hounded by climatic limitations. Further into this SERIES, we will be analyzing the historical evolution of roofing designs and functionalities in the context of Cambodia.
Prom is a Khmer term for roof capping. They can be found on roof ridges/hips and are traditionally made from ancient Khmer stucco — a combination of lime, sand, sugar and water.
Kompul Metre are roof spires typically found sitting on top of the PROM at the apex of a roof's ridge. Usually taking the form of blossoming lotus buds that are stacked on top of one another in a slender cone-like shape that tapers to the top.
Kveay is a decorative element that sits on top of every one of the PROM’s lower ends (at each corner of the roof). People can get very creative with these as they can come in many shapes/imageries. The most common form used on a residential dwelling is the “chicken’s tail” which symbolizes luck.
Dai Sna is a structural/decorative element of the roof that provides diagonal support. It is made from three pieces of wood that together form a right triangle and is typically placed in between the outer columns and the tip of the roof.
Rong Sbov are planks of wood that are placed just underneath the edges of the roof. It's mainly used to conceal the roof's structural elements (such as the purlins and rafters) from plain sight as well as to protect them from rainwater damages. The homeowner may choose to leave the RONG SBOV bare or decorate them with engravings or paintings of traditional kbach ornamentations.
Hor Jeang is the triangular space formed at both ends of a “Khmer” or “Rong” roof. Known in English as a “gable” or a “pediment”, a HOR JEANG can be part of the exterior wall or be a separate element all by itself. Typically, the HOR JEANG is where you can find the most elaborative ornamentations — especially for religious buildings. For residential buildings, however, decorations on the HOR JEANG are much more modest and simple.
The roof is perhaps the most significant element of traditional Khmer architecture – or at least in the sense of traditional Khmer wooden residences. It is so important, in fact, that the way it is built is the determining factor by which these vernacular dwellings are classified. Officially, there are 5 known types of traditional Khmer houses based on 5 different primary roof designs. However, a further inspection would suggest that there is an additional roof design/type that has not been counted in the official list but still plays an integral part in the region's architectural practice. These 6 types of residential roofs can be identified as: Khmer Roof, Rong Roof, Kerng Roof, Rong Doal Roof, Rong Deoung Roof and Pet Roof. The importance of the roof is no more evident than the naming scheme of the 5 traditional houses. Each house type is named after the type of roof that has been constructed over it. For instance, if a house is built with a “Pet roof” on top, then that house can be classified as a “Pteah Pet” or “Pet house”. For locals, choosing between which type of roof/house to build simply came down to regional popularity and customs as well as the economics or the social status of a family.
This is one of the two traditional roofs that take the “gable roof” form. But what makes this type of roof so distinct are its characteristically steep sides — the most efficient in facilitating heavy rainwater runoffs. Due to its costly nature, this style of roof/house has historically only been popular among the royals, nobles and temple residents and is among the least common types of houses built in the kingdom. Its steep pitch creates extra height. This means that it requires a lot more resources like longer pieces of logs and bigger quantity of tiles to construct.
This type of roof takes on a similar gable form as the KHMER ROOF but with a conventionally less steep pitch angle. RONG ROOFs could be traced all the way back to the Angkorian era where they were vividly depicted in numerous scenes on ancient bas reliefs — such as the ones found at Bayon. Among all types of roofs, RONG ROOFs are the easiest and most economic to construct for they require a lot less material and labor work.
This can be characterized by its distinctive overlaid double roof structure. The top tier takes the form of a “gable roof” and houses two gables/pediments, while the bottom tier is a half “hip roof” with a pitch angle that is a lot less steep compared to the pitch of the top tier. This type of roof is very expensive and often requires highly technical skills to build – thus, it was usually only found on houses of wealthy & high ranking individuals as well as on dormitories of Buddhist monks.
RONG DAOL ROOF is one of the two derivations of the preceding RONG ROOF. Sometime during the kingdom’s middle age (after the Angkorian period), people started to add lounging verandas to the front of their PTEAH RONGs, and over time, this front veranda element and its shed roof covering started to fully become a part of the main house. This new iteration of the RONG ROOF later became known as the RONG DAOL ROOF and was quite popular among families of various social classes.
Another variation of the RONG ROOF is the RONG DEOUNG ROOF – a succeeding adaptation of the RONG DAOL ROOF. With the introduction of the “Tbal Kdeoung” (a large traditional pestle and mortar set used to prepare ambok), locals started to extend on the back of their PTEAH RONG DAOLs by creating an annex that acted as an open storage unit to accommodate the “Tbal Kdeoung”. They also covered the space up by adding a shed roof on top. These back extensions naturally merged into the main house as a back hall, and the once RONG DAOL ROOF now finally became symmetrical when looked at from the sides. The name RONG DEOUNG is the shortened version of “Pteah Rong Dak Kdeoung” which means “Pteah Rong that stores the Tbal Kdeoung”.
Traditional PET ROOF is the Khmer equivalent to the western “hip roof”. It houses no decorative pediment/gable – a notable lack of feature that distinguishes it from the other types of traditional Khmer roofs. Its gentle slopes and relatively small total surface area make it quite cheap and easy to construct — a factor which contributed to its sudden surge of popularity during the reign of King Sisowath in the early 20th century. Initially, PET ROOFs were only commonly built on rest houses that scattered all along the kingdom's roads. But during the succeeding reign of king Sisowath Monivong, people started to adopt this style of roofing onto their own residential dwellings. And by the reign of king Norodom Sihanouk, this style accounted for almost all the roofs that were constructed during that era.
The origin of the PTEAH KANTAING muddied over time, and subsequently, so did its association with another primary typology of traditional Khmer housing, the PTEAH RONG. As described before, PTEAH RONG are relatively easy and cheap to construct by nature due to their simplistic form. This notion led the indigenous Khmer to often associate the PTEAH RONG typology to ‘poor people's settlements’, and by the reign of King Ang Chey (Trasak Paem) in the mid 14th century, locals started to slowly mass abandon this typology. It however started to gain popularity again, but this time, among the Chinese immigrants who were starting to settle down mostly along the Mekong River (Kampong Cham and Kratie). With its new synonymity with the Chinese, it later become known as PTEAH KANTAING instead of the original PTEAH RONG.
The thatch roof element is a fine example of Cambodia’s vernacular architecture. While other parts of the sugar palm can be utilized to create products such as the famed palm sugar, its leaves can be woven into relatively inexpensive thatch mattes. The leaves are woven together into panels in a centuries-old technique and are then left to dry. Afterward, they are placed and assembled on top of a bamboo skeleton to create a thatch structure. On one hand, straw is also regarded as a popular alternative to palm leaves and the techniques of their manufacturing are more or less the same. Despite thatch roof's obvious structural inferiority, its core advantage lies in how much cooler it can keep the interior space beneath it when compared to other roofing materials. Furthermore, it is lightweight — making it an ideal material choice to put on top of less substantial structures mostly found in the countryside.
Clay roof tiles are made from the same material and process as red clay bricks. Like the thatch palm mattes, clay tiles are also an ancient form of Khmer roofing that dates as far back as the 9th century — a technique that is still in practice to this day. They were widely used on temples and traditional wooden stilt houses of wealthy individuals. To this day, it is still highly prized for its amazing durability against the extremes of weather and its longevity — as is evidenced by remnants of surviving ancient tiles that are thought to have been used on ancient stone temples. Along with its well-known durability, the abundance of the region’s top clay soil as a resource has also undisputedly aided its popularization as the quintessential roofing material.
Nowadays, the most common type of metal used for roofing in the country is corrugated zinc. Quirks of its lightweight design, ease of workability and relative affordability have all made it become a staple for locals who are looking to build quick, cheap and easy structures/roofs. Mainly due to its enticingly affordable pricing, various disadvantages of these zinc sheets such as their tendency to create unpleasantly loud noises during rainstorms and how badly they age overtime are often initially disregarded altogether. However, despite these downsides, corrugated zinc sheets are quite a flexible material that can be used in a multitude of use cases. From zinc fences to zinc walls to zinc roofs, this material is virtually unavoidable within any urban setting in Cambodia.
Concrete tiles are also new to the Cambodian market. Because of the many similarities that they share with the traditional clay tiles, the former is often regarded as the best alternative to the latter. Implementing concrete tiles is just as easy as implementing clay tiles — in the sense that they both require an identical model of support structure. However, thanks to the convenience of concrete mass production, one gleaming advantage that concrete tiles have over their clay counterpart is the fact that they can be bought for just 1/3 of the latter’s price. Nevertheless, behind that tempting price tag, there are still some minor disadvantages to the tiles that need to be considered. For instance, concrete is heavier than clay, and thus, higher maintenance is likely required. The lifespan of a concrete tiled roof is also estimated to be a bit shorter than that of a clay tiled roof — exactly around 50 years shorter.
In the late 13th century, a Chinese diplomat by the name of Zhou Daguan paid a visit to Angkor and stayed at its royal court for almost a year. He is well-known for his detailed contemporary account of Angkor which has been helping archeologists to piece together the puzzle of Angkor's mysteries. Based on his record, we can conclude that by the time of his visit, the Khmer had already developed and had been using at least four types of roofing materials: lead tiles, yellow glazed tiles, unglazed tiles and thatch straw/palm leaves. Some archeologists speculate that these roofing materials may have also corresponded with the social structure of the time and only those who were of higher rankings may have been permitted with the privilege to use fancier materials. Unlike those high-ranking state officials, commoners, either rich or poor, may have not even been allowed to use proper tiling on their roofs. Instead, they were only left with the option of thatching.
A major challenge in building in hot humid climates is keeping the temperature of a living environment comfortably and consistently cool. The intense amount of heat that is being radiated daily from the tropical sun makes it extremely easy for spaces outside and inside of the home to pass heat around. A study conducted in 2007 showed that, as the part that has the largest surface area directly exposed to the sun, the roofing system is accountable for about 70% of the total heat gain in a building (Vijaykumar et al., 2007).
There are many smaller factors that can influence the rate at which a roof structure absorbs daytime heat such as a building's orientation and the roof's pitch angle. However, to yield a more substantial result, many passive cooling techniques can be applied to the roof to create comfort for its occupants. This, in turn, reduces the need for cooling through mechanical means – saving both the Earth's environment and the amount of money spent every year on energy bills.
Material selection is one of the most crucial parts of architectural design, not just in terms of aesthetic, but also in terms of comfort. Dense materials such as clay/cement tiles may seem to be efficient heat barriers at first, but in truth, they are major heat absorbers that play a big role in a building's heat gain during the night. Light materials such as thatch palm panels may not hold onto heat as long as dense clay/cement tiles do, but their perishability is the ultimate basis of their limitation. And although, light metals such as corrugated zinc might sound ideal in some aspects such as how easily it can dissipate back heat, metal's efficiency in heat conductivity can still make for an intensely unpleasant living experience during daytime. However, by choosing the right color and surface texture, a fraction of the heat can somewhat be alleviated. Lighter color and shinier surfaces are known to be better heat reflectors than the darker and more matte surfaces. Thus, it is always recommended that you choose lighter color tiles (such as white or light grey) instead of darker ones.
A poorly-designed roof system can trap quite an uncomfortable amount of hot air underneath its surface, while a thoughtfully-designed roof system with sufficient openings can help bring in natural ventilation and negate that problem. When cool air gets warmer, it tends to rise to a place of higher altitude. Thus, in most scenarios, hot air is found to accumulate just below the roofing structure. To provide any openings for hot air to escape through the roof is an efficient way to keep the indoor air temperature relatively livable. This passive technique can normally be achieved through two methods: stack ventilation and cross ventilation. In stack ventilation, cool air can enter through the lower parts of a home (usually through windows or air vents) and then rises to push hot air upward, out through the provided air gaps at the roof in a repeated process. In roof cross ventilation, openings are usually placed between the roof and the top walls which allows for constant air flow across from one side to the other.
One of the most expensive yet direct forms of passive cooling is the usage of thermal insulators. Generally speaking, a thermal insulator can prevent both heat loss and heat gain in a building and is used accordingly to the context of the site. There are many different forms/materials that a thermal insulator can come in. In Cambodia (where building heat gain is the main concern), shiny and highly reflective materials, usually aluminum foils, are used to bounce off heat. These materials usually come in thin sheets and in the context of the roof, are placed directly below the tiles or the rafters. However, it’s important to note that its underside must always come into contact with nothing but air as any contact with any other object could instead result in heat conduction – entirely defeating the purpose of the insulator. Despite its high cost, investing in one these insulation sheets might be worth the expense to some as such implementation has been proven to stop up to 80% of the heat that tries to penetrate into the home’s interior.
As its name suggests, a green roof is any roof that is integrated with greenery. A roof of this type is usually built either in the form of a flat roof or a slightly-sloped roof to functionally accommodate the growth of vegetation. Green roofs provide many economic benefits that, in the long run, can more than make up for its eye-watering upfront cost. It does this by consistently lowering the overall temperature of the roofing system which can also result in major energy cost savings. The vegetation grown on top of the roof also acts as a protective layer from the radiating sun, providing much needed shade for the roof's surface. They can also bring up the moisture level of their surrounding atmosphere through the process of photosynthesis. This can effectively help in reducing the heat island effect – a major problem faced by every compact urban area. Unfortunately, it is an extremely costly method. Not only does a green roof require high maintenance after it is built, it also involves complex structural design and work. Layers upon layers of soil and filtration networks work together in order to ensure that enough water is provided to sustain the plants’ livelihood as well as to make perfectly sure that the water being supplemented to the plants doesn’t cause any collateral damage to a building’s structural work. As a result, till this day, it can only mostly be found on high-end commercial buildings, and in environmentally-conscious cities like Singapore.