The place that incombustible wood is used Interior restriction

Interior restriction is not familiar who everybody consider to use incombustible wood
Decision of interior restriction is relating where most place that incombustible products is used
This page will simply expalain about point of interior restriction
Regarding information is as of home page update, it may be changed by revision
If you check acutual building or property, please check latest information

In the first place what is interior restriction ?

This is beginning the word that it was founded within Building standard low of 1959 because large-scale fires occurred frequently in public facilities. As purpose,while preventing frequent fires, delay the growth of initial fires, it is said that the interior materials used for walls or ceilimgs are restricted in order to ensure the safety of evacuation by reducing the occurrence harmful smoke and gas even if the fire expands

Buildings subject to interior restriction (under the buildings standard low)

As interior restriction regulation, Buildings standard low enforcement ordinance article 128-3 2 and 4, article 129, or article 112 are stated, a summary of the details is clearly described in the document published by Ministry of land infrastructure and transport.

Click image to enlarge

December 20,2017, Excerpt from Ministry of land infrastructure transport, Social capital development council achitecture subcommittee, Buildings standard system subcommittee,
Housing bureau document, Original link (
(The above document has exclusion provision that it is not applicable that are equipped with smoke exhaust equipment that complies with the provision article 126-3 of the order ordinance such as sprinklers and automatic)
(Also, areas and grades that require non-combustible and semi-incombustible materials are stipulated for fire protection compartment)

As above, basically, facilities where many people gather or windowless rooms are adapted interior restriction Except for some, basically it is required to use a material with performance that is more than semi-incombustible

Portion that interior restriction is adapted (under the buildings standard law)

Basically interior restriction apply to walls and ceilings as in the documents attached with links in the above items. Also as noted in the remarks column, the walls of living room are adapted to 1.2m or more parts, the interior restriction is not applied to parts such as baseboard and spandrel wall less than 1.2m in the wall surface.
(The wall surface of stairs or aisle are necessary to consider interior restriction because of all regulated basically)

December 20,2017, Excerpt expansion from Ministry of land infrastructure transport, Social capital development council achitecture subcommittee, Buildings standard system subcommittee, Housing bureau document, 44 pages.
Original link (

Precautions in the Scope applicable of interior restriction (There are difference each local government)

The regulations are as above for interior restriction under buildings standard law.
However, like below the detail stipulated in buildings standard law article 40

Article 40 local government depending on the local climates, or the use or scale of the special building, the provisions of this chapter or the command based on it alone will adequately acheve the purpose of building safety, fire prevention or sanitation. In cases where it is difficult, it is possible to add restrictions necessary on safety, fire prevention or hygiene regarding site, structure or building equipment of the buildings

As above, the criterion may be alleviated or added by ordinance of local government.
When using in a property, it would be appreciated if you check with building manager in your area.


・Interior restricution is stipulated by buildings standard law

・Facilities where many people gather is applied interior restriction

・According to regulations, in many cases, performance exceeding semi-incombustibility is required

・Interior restricution require the use of fire prevention materials (incombustible, semi-incombustible, flame retardant) for wall surface and ceilings

・In the living room, fire prevention materials are required for wall surface and ceilings of more than 1.2m

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