There are various types of roof shapes, and each shape has different characteristics. For rental properties, it's important to choose a roof shape that takes into account leak resistance and maintenance performance. After understanding the advantages and disadvantages, select the appropriate roof shape.
This article provides a clear explanation of the types and characteristics of roof shapes, types of roofing materials, and roofs commonly used in rental properties.
What Types of Roof Shapes Are There? What Are Their Characteristics?
There are roughly 9 types of roof shapes, each with different structures, costs, and durability. Rental property owners should prioritize maintenance and cost-effectiveness when making their selection.
Gable Roof (Kirizuma)
The gable roof is the most widely used roof shape worldwide. It has a simple structure with two symmetrical panels joined together, looking like an open book placed upside down.
The advantages are "low construction costs" and "good drainage with low risk of leaks." Due to its simple structure, ventilation and maintenance are easy, and it's also suitable for installing solar panels. Since various roofing materials can be chosen, it's attractive for matching both Japanese and Western-style designs.
The disadvantage is that the gable ends and bargeboards tend to deteriorate due to exposure to UV rays and rain and wind.
Hipped Roof (Yosemune)
The hipped roof is the second most popular roof type after the gable roof. The roof slopes down in four directions from the central ridge, creating a calm impression.
The advantages are high wind resistance and the ability to disperse and drain rainwater. It also reduces exterior wall deterioration.
The disadvantages are that the complex structure tends to increase construction and maintenance costs, and moisture tends to accumulate in the attic. It's not very suitable for solar panel installation.
Shed Roof (Katanagare)
The shed roof is the simplest shape, with a single panel sloping to one side. It creates a stylish, modern impression.
The advantages are reduced construction and maintenance costs, and easy installation of solar panels. By sloping toward the south, efficient power generation is possible.
The disadvantages are that during heavy rain or snow, there's significant stress on gutters with increased risk of leaks, and exterior walls tend to deteriorate faster.
Flat Roof (Roku/Riku)
A flat roof is a level roof without slope. It's used on buildings with rooftops and buildings, constructed with waterproof sheets rather than roofing materials.
The advantages are that the rooftop can be utilized, and cleaning and maintenance are easier.
The disadvantages are poor drainage, higher costs for waterproof coating, and reduced insulation performance.
Pyramid Roof (Hougyo)
The pyramid roof is a pyramid-shaped roof combining four triangles. Since it can only be used on square buildings, it's rarely seen in Japan.
The advantages are excellent earthquake and wind resistance, and low risk of leaks. It can distribute rain and snow evenly and is suitable for cold regions.
The disadvantages are that it's limited to square buildings, has poor ventilation, and is costly.
Offset Roof (Sashikake)
The offset roof has a stepped configuration where the first and second-floor roofs are at different levels. An exterior wall is created between the roofs, allowing windows to be installed there.
The advantages are excellent wind and insulation resistance, easy intake of natural light, and good ventilation. It's also suitable for solar panel installation.
The disadvantage is the risk of leaks, requiring measures for rain protection.
Irimoya Roof
The irimoya roof has a gable shape on top and a hipped shape below. It's a traditional design used in Japanese architecture since the Yayoi period, compatible with Japanese tiles and seen in Japanese-style buildings.
The advantages are excellent wind resistance, insulation, and ventilation. It creates a prestigious, high-class design with a sense of dignity.
The disadvantages are high construction and maintenance costs, and risk of leaks.
Gambrel Roof (Koshiore)
The gambrel roof has a gable roof with a slope that becomes steeper midway, resembling a shogi piece. Also called a gambrel roof, it's sometimes used in cold regions like Hokkaido and Tohoku.
The advantages are better drainage than gable roofs, and snow doesn't accumulate easily. The roof also deteriorates less easily.
The disadvantage is the risk of leaks from where the slope changes.
招き造り (Maneki-zukuri)
The maneki-zukuri is an asymmetrical shape combining a gable roof and a shed roof. It creates a highly design-oriented impression.
The advantages are good lighting and ventilation, and low risk of leaks. It combines the benefits of both gable and shed roofs.
The disadvantage is that, like gable roofs, the gable ends and bargeboards deteriorate easily.
What Types of Roofing Materials Are There? Comparing Characteristics by Material
Along with roof shape, selecting roofing material is important. Materials vary significantly in service life, maintenance frequency, and costs.
Slate
Decorative slate is a thin board-shaped roofing material made from a mixture of cement and fiber materials, characterized by being lightweight and low-cost. However, it breaks easily and requires painting maintenance every 10 years. Natural slate is a premium material using stone like slate, but is rarely used in Japan.
Galvalume Steel Sheet
Steel sheet plated with aluminum, zinc, and silicon. Despite being metal, it's rust-resistant and has a long service life. It has high earthquake resistance and can be installed on roofs with gentle slopes.
Zincalume Steel Sheet
Metal sheet with a surface coated with sand particles. The weaknesses of galvalume steel sheet regarding sound insulation and heat insulation are resolved, and it's rust-resistant and UV-resistant without requiring repainting.
Asphalt Shingle
Sheet-shaped roofing material coated with asphalt. It's low-cost, lightweight, and has high soundproofing and waterproofing properties, but has the disadvantage that few contractors can install it and moss and algae grow easily.
Ceramic Tile
Roofing material made from clay, available in glazed and unglazed types. Glazed types are highly durable and basically require no maintenance. They can match both Japanese and Western-style buildings.
Ceramic Board
A lightweight version of ceramic tile, with a very long service life of over 50 years and no repainting required. Although construction costs are high, it offers excellent long-term cost performance.
Corrugated Galvanized Iron Roof (Totan)
Roofing material of steel sheet with zinc plating. While construction costs are low and it's lightweight with high earthquake resistance, it has the disadvantage of a short service life of 10-20 years and rusts easily. It's rarely used currently.
Cement Tile
Tile made by hardening cement and sand. While construction costs are lower than ceramic tiles, production has now mostly ended.
Copper Sheet Roof
Traditional roofing material used in Japanese houses and temples and shrines. It has a service life of over 60 years and requires no maintenance, but disadvantages include almost no available contractors and high construction costs.
Why Are Flat Roofs Commonly Used in Rental Properties?
In rental properties, especially condominiums, flat roofs are most commonly used. There are two main reasons for this.
The first is securing construction space. With restrictions on building height and volume, making the roof flat allows maximum room capacity. Since adding one room increases rental income, this is a major advantage for owners.
The second is ease of management. Since condominiums are tall, sloped roofs increase risks during maintenance. With flat roofs, rooftop equipment can be inspected and managed safely, contributing to tenant satisfaction.
Waterproofing Methods Used for Flat Roofs
Waterproofing methods are essential for flat roofs to prevent leaks and corrosion. Here are four main methods:
- Urethane Waterproofing: The most commonly used method. Can flexibly adapt to uneven areas
- FRP Waterproofing: High waterproofing effect, dries quickly so often completed in one day. Lightweight and suitable for high-rise condominiums
- Sheet Waterproofing: Uses vinyl chloride or rubber sheets. High durability and can be applied to cracked areas
- Asphalt Waterproofing: Traditional method with excellent durability, but use is decreasing due to odor and fire concerns
What's Needed for Roof Maintenance? What Are the Cost Ranges?
Regular maintenance is essential for rental property roofs as well. Main methods and cost ranges are as follows:
Painting Work
Basic maintenance applying specialized coating to roofing materials. Frequency of once every 10 years is ideal. For approximately 30 tsubo, the cost range is 400,000-800,000 yen. Expensive coatings have higher per-application costs but longer service lives, which can be advantageous for total costs.
Roof Replacement Work
Method of removing all old roofing materials and replacing with new materials. Since the condition of the base can be confirmed, it leads to improved roof durability. Cost range for approximately 30 tsubo is 600,000-2,000,000 yen. Construction period may be lengthy.
Cover Method (Overlay Roofing)
Method of layering new roofing material over the current roof. Since removal of roofing material is unnecessary, construction period is short, and insulation and soundproofing also improve. Cost range for approximately 30 tsubo is 800,000-1,200,000 yen. However, there's risk of reduced earthquake resistance due to increased weight, so expert confirmation is necessary beforehand.
What Are the Benefits and Precautions for Installing Solar Power Generation on Rental Property Roofs?
It's possible to install solar power generation equipment on condominium and apartment roofs. Here we explain the main benefits and precautions.
Three Benefits of Solar Power Generation
- Emergency backup power: Can secure power in automatic operation mode during disasters
- Increased property value: If BELS certification is obtained, can promote as environmentally conscious property
- Effective roof utilization: Can reduce maintenance costs through common area power supply or electricity sales revenue
Precautions for Installation
- Power supply to all units may be difficult in existing condominiums
- Systems between 10kW and 50kW require self-consumption of 30% or more of generated power (2020 FIT revision)
- For condominium properties, permission from management association and residents is required
Roof Shapes Compatible with Solar Power Generation
Roofs compatible with solar panels are sloped roofs such as gable roofs and shed roofs. Flat roofs have risks regarding drainage capacity and require block stands, increasing costs.
By comprehensively considering roof shape, roofing materials, and maintenance methods, achieve stress-free rental management. Including solar power generation installation, roof selection with a view to long-term asset value maintenance is important.
Frequently Asked Questions (FAQ)
Q. What roof shape offers the best cost performance for rental properties?
Gable roofs offer the best cost performance. Construction costs are low, and drainage is good, so maintenance costs can also be kept down. The ability to accommodate various roofing materials is also a strength.
Q. How often should roof maintenance be performed?
Painting work is ideal once every 10 years. However, since it varies depending on roofing material type and environment, it's important to check condition through regular inspections.
Q. Why are flat roofs common on condominium roofs?
The main reasons are maximizing construction space (increasing rental income by securing more rooms) and ease of maintenance. For tall buildings, flat roofs can be managed more safely.
Q. When installing solar panels on a roof, what's the optimal roof shape?
Sloped roofs such as gable roofs and shed roofs are optimal. By sloping toward the south, efficient power generation becomes possible. Installation is also possible on flat roofs, but stands are required, increasing costs.
