Wired glass, a type of fire protection glass, is a key element in preventing the spread of fires. Its installation in certain areas is a legal requirement under the Building Standards Act, a robust regulatory framework designed to ensure fire safety. Preventing fire damage relies on effectively stopping its spread. Here are summarized the importance of installing wired glass and key considerations for its use.
1. What is wired glass?
2. Where to install wired glass?
- Fire Prevention Areas
- Quasi-fire Prevention Areas
3. Wired Glass Characteristics
- Not very strong
- Cracks due to heat
- Do not apply heat-resistant film to wired glass
4. Installing fire-protection glass without wire mesh
1. What is wired glass?
Wired glass (網入りガラス) is a type of fire protection glass for openings, which has a thin metal wire mesh inside. Even if the glass breaks during a building fire, the internal metal mesh holds the broken pieces together, preventing them from falling and stopping the fire from spreading through the opening.
Wired glass (網入りガラス)
2. Where to install wired glass?
Japan's Building Standards Act requires fire protection on buildings located in areas designated as "Fire Prevention Areas" and "Quasi-fire Prevention Areas." In these areas, any buildings that include commercial facilities, detached houses, and apartments must have wired-glass openings (within the Fire spread risk line) to prevent fire spread when it breaks out. The wired glass must be installed at the openings within 3 meters of the neighboring property line and the center line of the road on the first floor, and within 5 meters on the second floor and above.
Property line (隣地境界線) and Road centerline (道路中心線)
Openings of the house in this image are within 3m on the 1F, within 5m on the 2F from that line, and must be anti-fire-spreading.
Fire Prevention Areas (防火地域)
A Fire prevention area is designated by Urban planning (都市計画) to prevent the spread of fires. The primarily designated areas are commercial zones, around stations, and other high-density districts, where strict fire resistance is required. In the fire prevention area, buildings with three or more floors and a total floor area exceeding 100 square meters must be fire-resistant.
Quasi-fire Prevention Areas (準防火地域)
This area has fire-proof regulations that are less stringent than those for Fire Prevention Areas. The buildings in the designated density area must have fire resistance to prevent the spread of fire to neighboring places.
3. Wired Glass Characteristics
Not very strong
Wired glass may look strong due to the metal mesh inside, but it breaks easily. Its strength is similar to that of float glass, and it does not provide adequate security on its own. To improve the security of wired-glass windows, it is essential to install security bar grilles or shutters on the exterior.
Wired-glass window and security bars outside
Cracks due to heat
The metal wire inside the glass retains heat and expands when heated by sunlight. Wired glass may crack if it cannot withstand the heat expansion, depending on the environmental conditions in the sun.
Do not apply heat-resistant film to wired glass
Heat-resistant film (耐熱フィルム) applied to window glass blocks and absorbs sunlight, helping to maintain a stable room temperature. Although this film is designed for window glass, it cannot be applied to wired glass. The heat-resistant film can hold heat inside the wired glass, causing it to break.
In rental housing, such as an apartment, thermal cracking of glass is not considered an intentional or negligent act by the tenant; therefore, the owner will not charge the tenant for the repair. However, if the heat-resistant film causes a crack, the tenant will be charged for the cost. Additionally, in rental housing, tenants are generally not allowed to replace window glass on their own, as the windows are considered part of the common area.
A heat-resistant film (on the left) applied to a security glass
4. Installing fire-protection glass without wire mesh
On a sunny day, looking at the blue sky from a room would be nice - if the window were without annoying wire-meshed glass. Unfortunately, the standard option to follow the fire protection regulations is the installation of wired glass. Otherwise, openings must install tempered glass in addition to fire-resistant shutters, or double-glazed windows having the equivalent capability.
If you are planning to build a new house or renovate your existing one, consider using heat-resistant tempered glass as an alternative to wired glass. Make sure that the glass meets the standards established by the Ministry of Land, Infrastructure, Transport, and Tourism. The Building Standards Act requires that all openings in the outside walls of fire-resistant buildings and other at-risk buildings must have fire-stopping equipment. This equipment must be able to block flames for at least 20 minutes.
Reference
Designation Map for New Fire Prevention Regulations (Japanese)
https://www.toshiseibi.metro.tokyo.lg.jp/bosai/mokuzou_seibi/bouka/anzen_kuikizu
About fire protection windows (Japanese, PDF)
https://www.mlit.go.jp/common/001283290.pdf
