National Building Code of the Philippines

(d) Air Ducts . Air ducts passing through a floor shall be enclosed in a shaft. The shaft shall be as required in this Code for vertical openings. Dampers shall be installed where ducts pierce the shaft enclosure walls.r ducts in Group A Occupancies need not be enclosed in a shaft if conforming to the mechanical provisions of this Code. SECTION 1205. Floor Construction. (a) Floors shall be of such materials and construction as specified under Chapter 5 Fire- Zones and Fire-Resistive Standards and under Chapter 6 - Types of Construction. (b) All floors shall be so framed and secure into the framework and supporting walls as to form an integral part of the whole building. (c) The types of floor construction used shall provide means to keep the beam and girders from lateral buckling. SECTION 1206. Roof Construction and Covering. (a) Roof Covering . Roof covering for all buildings shall be either fire-retardant or ordinary depending upon the fire- resistive requirements of the particular type of construction. The use of combustible roof insulation shall be permitted in all types of construction provided it is covered with approved roof covering applied directly thereto. (b) Roof Trusses . All roofs shall be so framed and tied into the framework and supporting walls so as to form an integral part of the whole building. Roof trusses shall have all joints well fitted and shall have all tension members well tightened before any load is placed in the truss. Diagonal and sway bracing shall be used to brace all roof trusses. The allowable working stresses of materials in trusses shall conform to this Code. Camber shall be provided to prevent sagging. (c) Attics (1) Access . An attic access opening shall be provided in the ceiling of the top floor of buildings with a combustible ceiling or roof construction. The opening shall be located in a corridor or hallway of buildings of three or more storeys in height, and readily accessible in buildings of any height. An opening shall not be less than 600 millimeters square or 600 millimeters in diameter. The minimum clear headroom of 800 millimeters shall be provided above the access opening.  For ladder requirements, refer to the Philippine Mechanical Engineering Code. (2) Area Separation . Enclosed attic spaces of combustible construction shall be divided into horizontal areas not exceeding 250 square meters by fire-resistive partitions extending from the ceiling to the roof. Except, that where the entire attic is equipped with an approved automatic fire-extinguishing system, the attic space may be divided into areas not to exceed 750 square meters. Openings in the partitions shall be protected by self-closing doors. (3) Draft Stops. Regardless of the type of construction, draft stops shall be installed in trusses roofs, between roof and bottom chords or trusses, in all buildings exceeding 2000 square meters. Draft stops shall be constructed as for attic area separations. (4) Ventilation . Enclosed attics including rafter spaces formed where ceilings are applied direct to the underside or roof rafters, shall be provided with adequate ventilation protected against the entrance of rain. (d) Roof Drainage System. (1) Roof Drains . Roof drains shall be installed at low points of the roof and shall be adequate in size to discharge all tributary waters. (2) Overflow Drains and Scuppers . Where roof drains are required, adequate overflow drains shall be provided. (3) Concealed Piping . Roof drains and overflow drains, when concealed within the construction of the building, shall be installed in accordance with the provisions of the National Plumbing Code. (4) Over Public Property . Roof drainage water from a building shall not be permitted to flow over public property, except for Group A and J Occupancies. (e) Flashing . Flashing and counter flashing shall be provided at the juncture of the roof and vertical surfaces. SECTION 1207. Stairs, Exits and Occupant Loads. (a) General . The construction of stairs and exits shall conform to the occupant load requirements of buildings, reviewing stands, bleachers and grandstands: (1) Determinations of Occupant Loads . The Occupant load permitted in any building or portion thereof shall be determined by dividing the floor area assigned to that use by the unit area allowed per occupant as determined by the Secretary. (2) Exit Requirements . Exit requirements of a building or portion thereof used for different purposes shall be determined by the occupant load which gives the largest number of persons. No obstruction shall be placed in the required width of an exit except projections permitted by this Code. (3) Posting of Room Capacity . Any room having an occupant load of more than 50 where fixed seats are not installed, and which is used for classroom, assembly, or similar purpose shall have the capacity of the room posted in a conspicuous place near the main exit from the room. (4) Changes in Elevation . Except in Groups A Occupancies, changes in floor elevations of less than 300 millimeters along any exit serving a tributary occupant load of 10 or more shall be by means of ramps. (b) Exits (1) Number of Exits . Every building or usable portion thereof shall have at least one exit. In all occupancies, floors above the first storey having an occupant load of more than 10 shall not have less than two exits. Each mezzanine floor used for other than storage purposes, if greater in area than 185 square meters or more than 18.00 meters in any dimension, shall have at least than two stairways to an adjacent floor.  Every storey or portion thereof, having an occupant load of 500 to 999 shall have at least three exits. Every storey or portion thereof having an occupant load of 1000 or more shall have at least four (4) exits. The number of exits required from any storey of a building shall be determined by using the occupant loads of floors which exit through by using the occupant loads of floors which exit through the level under consideration as follows: 50 percent of the occupant load in the first adjacent storey above (and the first adjacent storey below, when a storey below exits through the level under consideration) and 25 percent of the occupant load in the storey immediately beyond the first adjacent storey. The maximum number of exits required for any storey shall be maintained until egress is provided from the structures. For purposes of this Section basement or cellars and occupied roofs shall be provided with exits as required for storeys. Floors above the second storey, basements and cellars used for other than service of the building shall have not less than two exits. (2) Width . The total width of exits in meters shall not be less than the total occupant load served divided by 165. Such width of exits shall be divided approximately equally among the separate exits. The total exit width required from any storey of a building shall be determined by using the occupant load of that storey plus the percentage of the occupant loads of floors which exits through the level under consideration as follows: fifty (50) per cent of the occupant load in the first adjacent storey above (and the first adjacent storey below when a storey below exits through the level under consideration) and twenty five per cent of the occupant load in the storey immediately beyond the first adjacent storey. The maximum exit width from any storey of a building shall be maintained.