91.7104.1. Site Testing. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Site testing of subsurface geological formations shall be conducted in accordance with the Methane Mitigation Standards. The site testing shall be conducted under the supervision of a licensed Architect or registered Engineer or Geologist and shall be performed by a testing agency approved by the Department.
The licensed Architect, registered Engineer or Geologist shall indicate in a report to the Department the testing procedure, the testing instruments used to measure the concentration and pressure of the methane gas. The measurements of the concentration and pressure of the methane gas shall be used to determine the Design Methane Concentration and the Design Methane Pressure. The Design Methane Concentration and the Design Methane Pressure shall determine the Site Design Level of LAMC Table 71.
EXCEPTION: Site testing is not required for buildings designed to the requirements of Site Design Level V as described in LAMC Table 71, or for buildings designed using the exceptions set forth in LAMC Subdivisions 91.7104.3.2 or 91.7104.3.3.
91.7104.2. Methane Mitigation Systems. (Amended by Ord. No. 185,587, Eff. 7/16/18.) All buildings located in the Methane Zone and Methane Buffer Zone shall provide a methane mitigation system as required by LAMC Table 71 based on the appropriate Site Design Level. The Superintendent of Building may approve an equivalent methane mitigation system designed by an Architect, Engineer or Geologist.
LAMC Table 71 prescribes the minimum methane mitigation systems, such as, the passive, active and miscellaneous systems, depending on the concentration and pressure of the methane present at the site. Each component of the passive, active and miscellaneous systems shall be constructed of an approved material and shall be installed in accordance with the Methane Mitigation Standards.
91.7104.2.1. Passive System. The passive system is a methane mitigation system installed beneath or near the building. The components of the passive system may consist of a de-watering system, the sub-slab vent system, and impervious membrane. The sub-slab vent system shall consist of Perforated Horizontal Pipes, Vent Risers, and Gravel Blankets for the purpose of collecting and conveying methane from the soil underneath the building to the atmosphere.
91.7104.2.1.1. De-watering System. The de-watering system is used to lower the ground water table to a level more than 12 inches below the bottom of the Perforated Horizontal Pipes. The de-watering system shall conduct ground water to an approved location.
91.7104.2.2. Active System. The components of the active system shall consist of one or more of the following, sub-slab system, gas detection system, mechanical ventilation, alarm system and control panel. All components shall be constructed of an approved material, installed in accordance with the Methane Mitigation Standards.
91.7104.2.3. Miscellaneous System. The components of the miscellaneous system may consist of Trench Dam, Cable or Conduit Seal Fitting, or Additional Vent Risers. The component of the miscellaneous system shall be a material approved by the Department and shall be installed in accordance with the Methane Mitigation Standards.
91.7104.3.2. Buildings with Raised Floor Construction. If a Building with Raised Floor Construction has underfloor ventilation construction in accordance with the standards below, then the utilities shall be installed with Trench Dams and Cable or Conduit Seal Fittings and a four inch thick gravel blanket shall be installed under and around the elevator pits.
Underfloor ventilation shall be provided by an approved mechanical ventilation system capable of exhausting underfloor air an equivalent of every 20 minutes, or by openings in the underfloor area complying with the following:
A. The top of the openings shall be located not more than 12 inches below the bottom of the floor joists.
B. The openings shall be distributed approximately equally and located to provide cross ventilation, for example, by locating the opening along the length of at least two opposite sides of the building.
C. The openings shall be the larger of:
1. Openings of not less than 1.5 square feet for each 25 linear feet or fraction of exterior wall; or
2. Openings shall be equal to 1 percent of underfloor area.
D. The openings may be covered with corrosion-resistant wire mesh with mesh openings of greater than ¼ inch and less than ½ inch in dimension.
A. The Unobstructed Openings shall exchange outside air.
B. The size of the Unobstructed Opening shall be the larger of:
1. Opening equal to at least 25 percent of the total perimeter wall area of the lowest level of the building, or
2. Opening equal to at least 25 percent of the floor area of the lowest level of the building.
C. The Unobstructed Openings shall be evenly distributed and located within the upper portion of at least two opposite exterior walls of the lowest level of the building.
Buildings with natural ventilation that are constructed as described above shall have the utilities constructed with Trench Dams and Cable or Conduit Seal Fittings. If there is an enclosed room or space less than 150 square feet (13.93 m2) within the building, then the enclosed room or space shall be constructed with vent openings that comply with the requirements of LAMC Subdivision 91.7104.3.4. (Amended by Ord. No. 185,587, Eff. 7/16/18.)
91.7104.3.4. Enclosed Room or Space within Building. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Individual enclosed rooms or enclosed spaces with floor area less than 2,000 square feet (185.80 m2) may be exempt from providing the Active System as required by LAMC Table 71, provided the vent openings comply with all of the following:
1. Vent openings are Unobstructed Openings, except screens made with at least 1/4 inch mesh or wind driven turbines on the roof shall be permitted.
2. The aggregate size of vent openings shall be the larger of either five percent of the total floor area of the room or the area of enclosed space, or ten percent of the area of walls on the perimeter of the room or enclosed space.
3. The vent openings shall be located to prevent the accumulation of methane gases within the room or enclosed space.
4. The top of the vent opening shall be located not more than 12 inches below roof joists or ceiling joists if located in a wall of a building.
5. The vent openings shall be located on either two opposite walls or two adjacent walls of the room or enclosed space if located in a wall of a building.
6. The vent openings shall be located no more than 50 feet from any point within the room or enclosed space.
7. When using wind driven turbine, the area of the vent opening shall be calculated by the area of the opening at the attachment of the wind driven turbine at the roof.
8. When the vent opening is located in a wall of an adjoining room, then the adjoining room shall be constructed of either an Active System, or have Natural Ventilation as described in LAMC Subdivision 91.7104.3.3.
91.7104.3.5. Single Family Dwelling. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Single Family Dwellings and buildings accessory to single family dwellings shall comply with all the Methane Mitigation requirements of LAMC Table 71, except that the following mitigation system may be substituted:
A. Single Station Gas Detectors with battery back-up may be installed in lieu of Alarm System and Gas Detection System; or
B. 6 mil thick Visquene may be used in lieu of Impervious Membrane, when the Site Design Levels are I or II; or
C. Additional Vent Risers or Mechanical Ventilation may be omitted for buildings with width less than 50 feet and footprint less than 6,000 square feet in area; or
D. Vent Risers may be substituted in lieu of Mechanical Extraction System, provided the Vent Risers are designed at a rate twice that established by the Methane Mitigation Standards.
91.7104.3.6. Buildings Located in the Methane Buffer Zone. A building, located entirely or partially in the Methane Buffer Zone, shall be designed to the requirements of the Methane Buffer Zone. Buildings located in the Methane Buffer Zone shall not be required to provide any methane mitigation system, if the Design Methane Pressure is less than or equal to two inches of water pressure and is either of the following:
A. Areas which qualify as Site Design Level I or II; or
B. Areas which qualify as Site Design Level III and the utilities are installed with Trench Dams and Cable or Conduit Seal Fitting.
A. If during the site testing, the groundwater level is deeper than 10 feet below the Perforated Horizontal Pipes, or
B. If the soil investigation or analysis, as approved by the Department, reveals the groundwater level is more than 12 inches below the bottom of the Perforated Horizontal Pipes.
91.7104.3.8. Buildings Located in the First Phase Playa Vista Project. The First Phase Playa Vista project, as approved by the City on September 21, 1993 and December 8, 1995, shall comply with the methane mitigation program as required by the Department pursuant to the Methane Prevention, Detection and Monitoring Program approved by the Department on January 31, 2001, in lieu of the requirements of this division.
91.7104.4. Paved Areas. Paved areas that are over 5,000 square feet in area and within 15 feet of the exterior wall of a commercial, industrial, institutional or residential building, shall be vented in accordance with the Methane Mitigation Standards.
EXCEPTION: Paved areas located in the Methane Buffer Zone and which qualify for Site Design Levels I, II or III.