Roof Refurbishment

The roof is one of the most important aspects to consider when purchasing and renovating a used property. If the roof is in good condition, you can continue to live in the property without any modifications to it. However, if the roof is aging, has structural issues, or if there are problems with the building's earthquake resistance, replacing the roof becomes necessary. Sometimes, a roof may be aging but not leaking, meaning it doesn't need immediate repairs. In such cases, while the replacement can be delayed, it is advisable to do it before moving in, as replacing a roof can generate a lot of dust.

If you haven't yet purchased a property and are still considering your options, the condition of the roof should be carefully inspected. Replacing an entire roof can be expensive, so even if a house is sold at a discount, poor roof condition could lead to higher overall costs.

Now, let's explore the types of roofs commonly found in Japan, the issues they might have, and where you should focus your attention.

Tiles with Clay Roofing

This traditional Japanese tile-roofing method is often seen on old houses, some around 100 years old. Unlike modern roofing, not all tiles are secured with nails or wires; many are simply placed on top of soil, which holds them in place. This poses a risk of tiles shifting and falling off during earthquakes or strong winds. Deteriorated soil can also fall from the roof, piling up on the ceiling or clogging the gutters.

Clay tile roofs are very heavy because the weight of the soil, in addition to the roof tiles, is placed on the building. This increases the risk of the house being crushed during a major earthquake. By removing the soil that holds the tiles and re-thatching the roof using modern construction methods, such as nails, the risk of collapse or tiles slipping off is greatly reduced. Recently, lightweight roof tiles, which are half the weight of regular tiles, have become available. Replacing the roof with these tiles can further reduce earthquake risks.

However, if older types of roof tiles that are no longer produced are used, it may be difficult to re-thatch the old tiles using modern methods. In such cases, replacing them with new tiles may alter the building's appearance and atmosphere. If preserving the building as a cultural asset or maintaining its original appearance is not a priority, re-thatching an earthen tile roof is safer. It is best to ask the real estate agent to confirm whether the roof is thatched or not.



This type of tile is called Hon-Kawara, the oldest and most prestigious style that retains the form of the original tiles from China and Korea. Hon-Kawara tiles are heavier than most tiles and require a solid building structure to support their weight. Therefore, they are typically used on sturdy buildings such as temples, shrines, and storehouses, but are rarely found on private homes.


The tile in this photo is called Shinogisan-Kawara. "Shinogi" refers to the ridge line on a Japanese sword or knife, where the angle meets the flat part of the blade. These tiles are named for their sharp ridge lines, resembling the Shinogi. Crafted by artisans before the industrialization of tile production, Shinogisan-Kawara tiles are now rare, with only a few companies offering reproductions. They feature beautiful, sharp vertical lines, and replacing them with modern rounded tiles would significantly alter the roof's appearance.
Installing these tiles requires the expertise of a skilled roofer to ensure they look beautiful, and the difficulty increases if the traditional clay roofing method is not used. In older urban areas where buildings are densely packed, smaller tiles are sometimes used to maintain visual balance, even in smaller structures. Replacing these with standard-sized tiles would disrupt the building's aesthetic harmony.


Rounded Japanese-style roof tiles are commonly used today. It can be challenging for the general public to determine by appearance alone whether a roof is thatched with soil or secured with nails or wires, as even new-looking tiles may be part of an earthen roofing system.

Cement Tile

These tiles became popular from 1955 to around 1975 because they were less expensive than traditional tiles. However, the water resistance of cement tiles is not very high. Originally, the surface of the tiles was painted to improve their waterproofing, but this coating needs to be reapplied every 10 years to maintain effectiveness. Unfortunately, most houses are not repainted regularly, leaving the tiles in a dilapidated state as the surface paint peels off.

As cement roof tiles age, they become more susceptible to cracking and moss growth, which reduces drainage and increases the risk of leaks. If cement tiles have been properly repainted, they may still be usable, but generally, it is better to replace them to ensure the roof's integrity.


Cement tiles can vary in condition: some have peeling and deteriorating paint, some are cracked and causing leaks, while others remain intact with their black paint still in good condition. The tiles in this photo are flat, but some cement tiles are shaped like traditional Japanese-style tiles.

Sheet Metal Roofing

Metal plate roofs are lighter than tiles and more resistant to earthquakes, but they are less durable than tile roofs. They rust over time and often require periodic painting or replacement, depending on the type of metal and location. Copper shingle roofing, used in rare old houses, is prestigious and does not require painting, as the corrosion and aging process stops once the copper turns verdigris. However, this option is quite costly.

For all sheet metal roofs, proper attic insulation is crucial. Without it, the house can become extremely hot in the summer and very cold in the winter. Additionally, without soundproofing, the noise from rain hitting the metal roof can echo loudly through the house.

If a secondhand property has a sheet metal roof, it should typically be re-roofed if it has been more than 30 years since installation. Even if the roof is newer, it may need replacement if it hasn't been regularly painted, or if the house is near the ocean or other areas prone to severe rusting. While replacing a sheet metal roof is often less expensive than a tile roof, the costs of repainting and reroofing, including hiring a contractor, might not be significantly different from those of a tile roof. Therefore, maintenance costs should be factored into the overall roofing cost.

For a more cost-effective option, you can replace the roof yourself with corrugated sheets from a home improvement store or sheet metal purchased online. However, be aware that replacing a roof is dangerous for amateurs due to the risk of falls and other hazards.


A rusted sheet metal roof can be handled in different ways depending on the severity of the rust. If the rust is superficial, it can be sanded off and the roof can be repainted. However, if the rust is deep or there are holes, the roof will need to be replaced.

Slate Roofs

There are many different types of slate roofing, so I won't delve into specifics here. However, it's crucial to note that slate tiles and slates used on buildings constructed before 2004 may contain asbestos. While asbestos is mixed into the material and molded, posing no immediate danger unless disturbed, the disposal costs are considerably higher than for regular roofing materials. If you're informed by a real estate agent that the roof is made of slate tiles, it's advisable to inquire about the manufacturing date of the slate tiles and whether they contain asbestos.

Flat Roof

Many buildings, including reinforced concrete structures, feature flat rooftops. While Japan doesn't experience rainfall as intense as subtropical regions, heavy rains during the rainy season and summer are common. Additionally, the strong sunlight in summer can cause tarps and waterproof coatings on rooftops to deteriorate faster, necessitating periodic reapplication and other maintenance measures. It's not uncommon for older concrete buildings to develop leaks due to inadequate maintenance. Furthermore, if cracks are detected in the roof or walls, repairs will be necessary, so it's wise to anticipate higher repair costs. If the rooftop is in good condition and the structure is simple, you may be able to lower maintenance costs by painting the waterproofing yourself.

Cases of Roof Structure Problems

In some instances, houses that have undergone extensions or remodeling, or buildings with complex construction, may encounter issues with the roof structure. The "valleys" of the roof are especially vulnerable to leaks, as rainwater from the roof collects in these areas, potentially leading to clogs or deterioration caused by leaves and debris.

Moreover, buildings featuring what's known as "Kanban-Kenchiku" or billboard architecture―where only the front of a wooden house is adorned with mortar to mimic a Western-style concrete building―or those with forcibly built terraces on the roof, often have structures prone to leaks. This occurs because there's nowhere for rainwater to escape if the gutters become blocked. Regular gutter cleaning or even modifying the roof structure itself can help prevent leaks. However, many roof structures are not easily accessible for amateur gutter cleaning, and modifying the structure is a costly and extensive process. Essentially, a complex roof structure requires additional funds for renovation and maintenance, so those aiming to minimize their budget for such work should avoid purchasing such roofs.

Interestingly, the unnecessarily intricate roof structures sometimes observed in traditional Japanese wooden houses may reflect the sense of beauty, wealth, and prestige of the homeowners. If you're captivated by the beauty of such architecture and are willing to invest in preserving it, it's worth considering spending the necessary funds to maintain it. Nowadays, most Japanese houses are prefabricated with simple structures that can be built quickly and affordably, leading to the gradual disappearance of Japanese architecture featuring prestigious and complex roofs.



Takei Sanshodo (left) & Hanaichi Flower Shop (right), at Edo-Tokyo Open Air Architectural Museum. From Wikipedia Commons.
This building is an example of what's known as "billboard architecture." Often, the area between the concrete-style wall and the roof of the wooden house forms a valley, which is especially susceptible to leaks. Billboard architecture was popular from the mid-1920s to the 1980s among individuals who couldn't afford to build concrete structures. While some enthusiasts engage in preservation efforts due to the kitschy charm of these buildings, many are being lost to reconstruction or demolition.

What to Consider When Asking for an Estimate

Beyond just the roof area, the cost of roof repair hinges on various factors like the roof structure, height from the ground, required scaffolds, disposal expenses for old materials, and transportation costs. Consequently, it's impossible to ascertain the total cost until you request an estimate.

Upon soliciting estimates from several companies, I discovered significant variations in pricing. For instance, a tile roof was priced over one million yen higher than a sheet metal roof. Moreover, there was approximately a one million yen gap between the highest and lowest estimates received for a sheet metal roof. Hence, I highly recommend seeking estimates from multiple companies and comparing them. Fortunately, in Japan, most companies offer free estimates.

However, it's essential to recognize that each company adopts its own approach to estimation. Some may provide rough estimates based on market prices per square foot, while others might base their estimates on the lowest or highest possible costs. Consequently, a rough or low estimate might lead to higher costs upon completion, whereas a high estimate could result in lower final expenses. Additionally, it's not uncommon to discover structural damage beneath the roof of older properties during repairs, potentially exceeding the original estimate by a considerable margin.