Chapter 15.24 — DESIGN REQUIREMENTS

The minimum wind speeds are established for the Town of Mammoth Lakes, including the Mammoth Yosemite Airport:

(1)

One- and two-family dwellings (R-3 occupancies): 95 miles per hour (mph), nominal design three-second gust wind speeds.

(2)

Residential structures other than one- and two-family dwellings (R-3 occupancies) and non-residential structures, nominal design three-second gust wind speeds:

a.

Ninety miles per hour for Risk Category I buildings and other structures.

b.

Ninety-five miles per hour for Risk Category II buildings and other structures.

c.

One hundred miles per hour for Risk Category III buildings and other structures.

d.

One hundred five miles per hour for Risk Category IV buildings and other structures.

(Code 1990, § 15.24.010; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019; Ord. No. 22-11, § 3(exh. A), 12-7-2022)

All structures within the boundaries of the Town shall be designed to seismic ground accelerations per the most recent data on the USGS seismic design maps and as defined in the California Building Code. A minimum of 20 percent of the design snow load (Pf) shall be added to the dead load for seismic design.

(Code 1990, § 15.24.020; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

The following shall be considered minimum design standards for calculations within the guidelines established by the 24 CCR Part 6:

(1)

The Town shall be considered within Climatic Zone 16 as defined by the State Energy Commission.

(2)

Winter design temperature shall be minus two degrees Fahrenheit.

(3)

Summer design temperatures shall be 74 degrees Fahrenheit.

(4)

Heating degree-days shall be 8,000.

(Code 1990, § 15.24.030; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

(a)

The Town shall be considered a snow area. All structures within the Town shall be designed to withstand snow loads and any additional effects created by snow.

(b)

Ground snow load (Pg) is established as follows:

(1)

100 pounds per square foot for Mammoth Yosemite Airport;

(2)

230 pounds for elevations 8,500 feet or less;

(3)

300 pounds for elevations greater than 8,500 feet.

(c)

Roof snow load (Pf) shall be established per equation 7.3-1 of ASCE 7-22:

0.7(Ce)(Ct)(Pg)

Ce = Exposure factor

Pg = Ground snow load

Ct = Thermal factor

(1)

The exposure factor (Ce) shall be determined per ASCE 7-22:

Ce = 1.0 Partially exposed roofs

Ce = 0.9 Fully exposed roofs on all sides with no shelter from terrain, trees or higher structures

Ce = 1.2 Sheltered

(2)

Reserved.

(3)

The thermal factor (Ct) shall be determined per ASCE 7-22:

Ct = 1.2 for unheated and open-air structures, structures kept just above freezing [40° to 50° F (4° to 10° C)], and other structures with cold, ventilated roofs meeting the minimum requirements of the current edition of the California Energy Code.

Refer to ASCE 7-22 Table 7.3-3 for heated structures with unventilated roofs, and ASCE 7-22 Table 7.3-2 for all other structures.

(4)

Snow load reductions for roof pitch will be permitted per ASCE 7-22, provided the roof design does not allow snow to accumulate from ground level to the roof eave. This shall be assumed to be a minimum of ten feet from eave to grade level. Design consideration shall be given to drifting snow and other accumulations on the roof, exposure, impact, effects on adjacent property, and other dynamic loading due to snow avalanching onto lower structural elements, against projections such as vents, and onto targets on the ground.

(5)

Setbacks to property lines (for snowshed impact zones).

a.

All eaves of sloped roofs (>2:12) shall maintain setbacks so that snowshed impact areas will occur on the property of the subject structure. The minimum impact area setback shall be ten feet measured horizontally from a vertical line projecting from the roof eave to the property line.

b.

The eaves of a structure may encroach into the impact area setback a maximum of three feet, provided an engineered snowslide restraint device, designed in accordance with the provisions of this Code, is incorporated into the roof design.

c.

Property owners shall maintain snowshed impact areas to prevent snow from encroaching onto adjacent properties.

(6)

Protection of required entries/exits, parking, and driveways.

a.

The roof and eaves of all structures shall be designed so that snowshed impact areas will not occur in or on entries/exits (required exits only for R-3 occupancies), vehicle parking areas, driveways, LPG storage tanks, walkways, and public ways. The minimum snowshed impact area shall have a setback of ten feet measured horizontally from a vertical line projecting from the roof eave to the aforementioned improvement.

b.

The snowshed impact area may be eliminated provided an engineered snow restraint system, designed in accordance with this Code, is incorporated into the roof design and, in other than R-3 occupancies, an approved roof drainage system (e.g., heated gutter and downspout) is installed to prevent ice formation/accumulation at the grade or access level.

c.

Property owners shall maintain snowshed impact areas to prevent snow from encroaching beyond the impact area boundaries.

d.

Existing structures may use engineered snowslide restraint devices without an approved roof drainage system to reduce hazards associated with the existing roof design.

(7)

Projections such as plumbing vents, equipment vents, and similar elements, which penetrate the roof, shall terminate within 36 inches of the ridge or uppermost portion of the roof area. Mechanical vents and air intakes installed on vertical surfaces shall terminate a minimum of 12 feet above grade when not subjected to shedding roof snow, and a minimum of seventeen feet above grade when subjected to shedding roof snow.

(8)

Overhead electrical service weatherheads and similar utility connections shall not be located in any area subject to damage from sliding snow or ice. Weatherheads may project through the roof with a riser constructed of two-inch minimum diameter rigid galvanized steel conduit, provided no alternative locations are available and the Building Official and servicing utility have approved the location.

(9)

A roof projection such as a fireplace chase, parapet or similar structure, which could be subjected to sliding snow or ice, shall be designed for these horizontal forces (Fs).The resultant moment produced from Fs shall be applied to the mid-height of the projection.

Fv (for roof projections) = L (0.5L + B) Pf

Fv (for snow retention devices) = L (B) Pf

Fs = Horizontal load against roof projection, pounds

Fv = Snow weight against projection, pounds

X = Vertical component of roof slope (rise), feet

Y = Horizontal component of roof slope (run), feet

L = Horizontal distance between projection and ridge, feet

B = Width of projection, in feet. Not to exceed six feet

Pf = Minimum roof snow load, pounds per square foot (PSF)

(10)

Projections shall be protected with an ice splitter or cricket. All ice splitters shall be constructed the full width of the projection base and shall terminate not lower than the midpoint height of the projection.

(11)

Snow rails, roof cleats, and similar snowslide restricting devices shall be designed using the formula set forth in Subsection (c)(9) of this section, except calculations for Fv need only consider the tributary load area of the device. Snowslide restraint devices shall be installed within the first three feet of the roof eave and spaced per the design of the system.

(12)

Warm roofs that drain water over the eaves shall be capable of supporting 2.0 times Pf at the overhang when the roof is unventilated with insulation R-value of less than 30 or ventilated roofs with R-values less than 20.

(13)

All roof systems shall consider the effects of ice dams and shall be designed to prevent water infiltration at the eaves. As a minimum, the underlayment at the eaves shall consist of two layers of Type 15 felt solid cemented together with an approved cementing material or other approved equivalent material. The ice dam protection shall extend from the eave to a line six feet inside the exterior wall line of the building.

(Code 1990, § 15.24.040; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019; Ord. No. 2025-07, § 3(Exh. A), 12-17-2025)

Every new structure, and every existing structure when 50 percent or more of the total roof area is re-roofed within any one-year period, shall have a fire retardant roof covering that is at least Class A as defined in the California Building Code, as adopted and amended by the California Building Standards Commission. The installer of the roof covering shall provide certification of the roof covering classification to the building owner and, when requested, to the Town Building Division. The installer shall also install the roof covering in accordance with the manufacturer's listing.

(Code 1990, § 15.24.045; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

It shall be the responsibility of the contractor/installer to protect concrete installed in cold weather (below 40 degrees Fahrenheit). The Building Division may monitor foundation site temperatures during cold months. When foundation temperatures are below freezing within the first seven days of curing, special engineers' reports may be required.

(Code 1990, § 15.24.060; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

A building permit shall be required for retaining walls exceeding four feet in height or retaining walls supporting any surcharge or special loads. A professional engineer licensed in the State shall design such walls.

(Code 1990, § 15.24.070; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

(a)

Liquefied petroleum gas (LPG) burning appliances shall not be installed in an above-grade, under-floor space, attic area, or basement unless the location is provided with an approved method for the removal of unburned gases. Approved ventilation methods shall extend to the outside and terminate at an unobstructed area (an area not subject to snow accumulation). Other methods are subject to the approval of the Building Official.

(b)

LPG appliance vents, which extend through the roof shall terminate within three feet of the ridge or uppermost portion of the roof. Vents, which extend through a wall or other vertical surface shall terminate a minimum of 12 feet above grade when not subjected to shedding roof snow, and a minimum of 17 feet above grade when subjected to shedding roof snow.

(c)

Exceptions.

(1)

New LPG appliance vents which extend through the roof of existing structures shall terminate within three feet or as close as practical to the ridge or uppermost portion of the roof. Terminations greater than three feet below the ridge shall be protected by an approved means.

(2)

New LPG appliance vents which extend through a wall or other vertical surface of an existing structure shall terminate as high as practical above grade. The installer shall furnish the owner or post in a conspicuous location, instructions to maintain vent clearances.

(Code 1990, § 15.24.085; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

(a)

All Group R occupancies containing liquefied petroleum gas (LPG) appliances and/or LPG facilities shall be equipped with a listed LPG sensing device (sensor) attached to an audible alarm. Sensors shall be installed on the lowest floor of the dwelling unit and in the lowest portion of any crawlspace area. Sensors shall be connected to an alarm audible throughout the living areas. Sensor/alarms in new construction shall be hardwired and interconnected. Sensors and alarms are not required to be hardwired and interconnected in

existing areas of buildings undergoing alterations, additions, and repairs that do not result in the removal of interior wall or ceiling finishes exposing the structure. In accessible units, alarms shall be audible and visual.

(b)

Exceptions:

(1)

Centrally located LPG appliances and facilities serving multiple units need not provide alarms to all living areas provided, if in the opinion of the Building Official, adequate notification can be relayed to all occupants.

(2)

Sensors located in individual units within a multifamily structure equipped with a fire warning system may have alarms independent of the main alarm system. Required sensors located in crawlspace areas, equipment rooms, and similar areas shall be connected to alarms that are audible and visual, and continuously monitored.

(c)

Sensors and alarms shall be installed when the valuation of new construction, additions, alterations and repairs of a Group R occupancy exceeds $1,000.00 and a permit is required.

(Code 1990, § 15.24.086; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019; Ord. No. 2025-07, § 3(Exh. A), 12-17-2025)

Potable water supply and drainage systems outside buildings or structures shall be installed per the standards established by the Mammoth Community Water District. The minimum depth of water supply piping shall be four feet below grade.

(Code 1990, § 15.24.090; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

To protect underfloor plumbing, the perimeter of the crawlspace area shall be insulated. Concrete or masonry stem walls, and framed foundation (cripple) walls shall be insulated with a material having a minimum R-Value based on the latest version of the California Energy Code.

(Code 1990, § 15.24.095; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

Loft Flowchart

(a)

Definitions. The following words, terms and phrases, when used in this section, shall have the meanings ascribed to them in this subsection, except where the context clearly indicates a different meaning:

Addition means an extension or increase in floor area or height of a building or structure.

Alteration means any construction or renovation other than a repair or addition. For purposes of this chapter, a remodel of any kind shall be considered an alteration.

Bedroom means a space, area, or partitioned part of the inside of a building enclosed by walls, ceilings, or doors and used by the building occupants for overnight sleeping purposes, and separated from other spaces, areas, or parts of the building.

Emergency escape and rescue opening means an operable window, door, or other similar device that provides for a means of escape and access for rescue in the event of an emergency.

Exit access travel distance means the distance building occupants must travel from the most remote point within a dwelling to a grade level exit. The term "exit access travel distance" is the maximum overall travel distance from the most remote point of a loft or loft bedroom to a grade level exit.

Loft or mezzanine means an intermediate level or levels between the floor and ceiling of any story of a building that is open to the room in which the loft is located. For purposes of this section, lofts used for residential overnight sleeping purposes shall be addressed. Lofts in residential occupancies shall be considered sleeping areas.

New construction means a newly constructed building that does not include additions, alterations, or repairs, and is a building that has never before been used or occupied for any purpose.

Public way means a street, alley or other parcel of land open to the outside air leading to a street, that has been deeded, dedicated or otherwise permanently appropriated to the public for public use and which has a clear width and height of not less than ten feet.

Repair means the reconstruction or renewal of any part of a building for the purpose of its continued maintenance or to correct damage.

Technically infeasible means an alteration of a building or facility that has little likelihood of being accomplished because the existing structural conditions require the removal or alteration of a load-bearing member that is an essential part of the structural frame, or because other existing physical or site constraints prohibit modification or addition of elements, spaces or features that are in full and strict compliance with the minimum requirements for new construction.

(b)

Loft requirements for new construction, additions, alterations, and repairs.

(1)

All lofts in new construction, additions, alterations, and repairs shall comply with the applicable minimum standards in the latest version of the California Building Standards Code (24 CCR), including Appendix P ("Sleeping Lofts"). A building permit will be required for this type of work.

(2)

Alternative methods of construction may be considered on a case-by-case basis by the Building Official for additions, alterations, and repairs, with technical infeasibility needing to be demonstrated in each case. For purposes of this section, the provisions in Subsection (c) of this section may be considered for alternative methods of construction.

(c)

Loft requirements in existing structures.

(1)

Applicability and enforcement. The construction standards in this section shall apply to all existing lofts in residential occupancies in the Town. Enforcement of these construction standards shall be limited to applications for a business tax certificate pursuant to overnight transient rental purposes, or when otherwise required in connection with a building permit. It shall be the responsibility of the private outside third-party inspector hired by the business tax certificate applicant to ensure compliance with this section in order to allow for overnight transient rental use.

(2)

Existing stairs, handrails, head heights, guardrails, and floor areas in lofts already used for residential overnight sleeping purposes will be considered as compliant based on prior Uniform Building Code (UBC) standards as follows:

a.

For all stairs, the maximum stair riser height shall be eight inches, and the minimum stair tread depth shall be nine inches.

b.

The minimum clear width for loft stairs shall be 30 inches.

c.

Loft guardrails shall be a minimum of 36 inches and a maximum of 42 inches in height as measured above the finish floor or walking surface at the open sides of lofts. Guardrails at loft stairs shall be no less than 34 inches as measured above the stair nosing. Intermediate members in open type railings shall be space no more than nine inches apart on-center. The distance between the top of a guardrail and ceiling or projection directly above it shall not be less than 24 inches.

d.

The minimum ceiling height at lofts shall be seven feet, and seven feet six inches in habitable rooms. If any habitable room has a furred ceiling, the prescribed ceiling height is required in two-thirds of the area thereof, but in no case shall the furred ceiling be less than seven feet. For rooms with sloped ceilings, the required floor area of the room shall have a ceiling height of not less than five feet and not less than 50

percent of the required floor area shall have a ceiling height of not less than the minimum heights as required for the room or space under consideration.

e.

The headroom at stairways shall not be less than six feet, six inches measured vertically from the sloped line adjoining the tread nosings from the floor surface of the stair landings.

f.

A minimum of 70 square feet is required for the net clear floor area for lofts, bedrooms accessed through lofts, and other habitable rooms that are located in or accessed through lofts.

g.

The total floor area of a loft shall not exceed one-third of the floor area of the room in which the loft is located.

Exception 1. The maximum one-third allowable floor area limitation may be exceeded in existing lofts if the exit access travel distance does not exceed 100 feet to a grade level exit.

Exception 2. The floor area of a loft may be one-half of the floor area of the room or space in which the loft is located if the following conditions are met:

(i)

The building is equipped with an automatic fire sprinkler system.

(ii)

The loft is fully open to the room in which the loft is located, except enclosed closets and bathrooms.

(iii)

The loft is unobstructed except for walls not more than 42 inches in height, columns and posts.

h.

Stair handrails are required on only one side of a loft stairway. Stair handrails shall be placed no less than 30 inches nor more than 38 inches above the nosing of the treads. Handrails projecting from a wall or guard shall have a space of not less than 1½ inches between the wall or guard and the handrail. The hand grip portion of handrails shall not be less than 1¼ inches nor more than two inches in cross sectional dimension. The ends of handrails shall terminate into a post, wall, or floor.

Exception: For handrails not conforming to the cross sectional dimensions as set forth above, an equivalent graspability for the handrail shall be provided. Approval for handrail equivalent graspability shall be determined by the Building Official on a case-by-case basis.

i.

Spiral stairs are allowed. Spiral stair criteria is as follows:

Spiral stairways may be used when the total area served is 400 square feet or less.

The stair treads must provide a clear walking area measuring at least 26 inches from the outer edge of the supporting column to the inner edge of the handrail.

A tread depth of at least 7½ inches must be provided at a point 12 inches from where the tread is narrowest as measured at a right angle to the stair nosing.

The rise must be sufficient to provide a minimum of six feet, six inches headroom.

Stair risers shall not exceed 9½ inches in height.

(3)

All lofts and rooms in or accessed through lofts shall have smoke and carbon monoxide detectors installed per the latest edition of the California Building Code. The installation of hard-wired or wireless smoke and carbon monoxide detectors, and combination smoke/carbon monoxide detectors are allowed.

(4)

Emergency escape and rescue openings are required in all lofts and loft rooms that are used for overnight sleeping purposes.

a.

Exceptions:

Emergency escape and rescue openings are not required in lofts when 50 percent or more of the loft's perimeter that is common to the room in which the loft is located is open to below. Guards no less than 36 inches in height are required, and walls and guardrails not more than 42 inches in height, columns and posts are allowed at the area that is open to below.

Emergency escape and rescue openings are not required in lofts when the building is equipped with an operable automatic fire sprinkler system.

Emergency escape and rescue openings are not required in lofts when all of the following conditions are met:

(i)

A minimum of 25 percent of the building's perimeter adjoins or has access to a public way or open space, or when the distance between adjacent buildings is at least 1½ times the height of the building under consideration. The final determination for compliant street frontage shall be made by the Mammoth Lakes Fire Protection District.

(ii)

The exit access travel distance is no greater than 100 feet.

(iii)

Wireless or hardwired smoke and carbon monoxide detectors are installed in the loft and in all loft rooms used for overnight sleeping purposes. The smoke and carbon monoxide detectors must be interconnected with all other smoke and carbon detectors within the dwelling unit.

b.

The creation of a new opening in an exterior wall for lofts in buildings without complying street frontage is not allowed when the building also does not have an existing emergency escape and rescue opening, complying openness, and an operable automatic fire sprinkler system.

c.

New or altered emergency escape and rescue openings shall comply with the standards found in the latest version of the California Building Code. For existing emergency escape and rescue openings, the minimum requirements shall be as follows:

The minimum net clear opening width must be 20 inches.

The minimum net clear opening height must be 24 inches.

The minimum net clear total opening must be five square feet.

The maximum sill height shall be 48 inches above the finish floor.

Exception: Existing emergency escape and rescue openings may have a sill height that exceeds 48 inches when technical infeasibility is determined by the Building Official on a case-by-case basis. If technical infeasibility is demonstrated, a ladder or steps shall be provided that meets all of the following criteria:

i.

The ladder or steps must be permanently installed.

ii.

Ladder rungs or steps must have an inside clear width of at least 12 inches.

iii.

Ladder rungs or steps shall project no less than three inches from the wall.

iv.

Ladder rungs or steps shall be spaced not more than 18 inches on center vertically for the full height between the floor and the opening.

v.

The ladder must be centered directly under the operable part of the window.

(5)

Bedrooms in lofts or accessed through lofts shall comply with the floor area, ceiling height, and emergency escape and rescue standards as identified in this section. In addition, carbon monoxide and smoke detectors shall be installed as required by the latest version of the California Building Code.

(6)

A legally compliant storage area will have no more than one switch controlled light for every 70 square feet of usable floor area, and no more than one plug receptacle, and no furniture in that room that could support living, sleeping, or cooking. Bathrooms and closets are not included in the determination of legally compliant rooms in existing lofts.

(7)

Other habitable rooms in lofts or accessed through lofts that are not used for overnight sleeping or storage purposes shall have ceiling heights, floor areas, and carbon monoxide and smoke detectors that comply with this section.

(8)

a.

Unit owners who have a noncompliant loft but would like to rent the unit on a transient basis, may allow the occupants who would usually sleep in the loft to use other habitable areas of the unit for sleeping purposes, notwithstanding the requirements of Chapter 5.32. Allowable habitable areas to be used for sleeping purposes outside of a noncompliant loft includes other bedrooms, living rooms, dining rooms, and family rooms.

(Code 1990, § 15.24.100; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019; Ord. No. 2025-07, § 3(Exh. A), 12-17-2025)

Footings and foundations shall extend below the frost line. The frost line shall be considered a minimum of 24 inches below grade.

(Code 1990, § 15.24.110; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

Design for structures within flood hazard areas shall be per the requirements established in the most recently adopted floodplain management ordinance.

(Code 1990, § 15.24.120; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)

The Building Official may approve temporary structures associated with current or future development projects. Use and/or occupancy of such structures shall be limited to the time established by the permit, but not to exceed three years. The Building Official may consider reduced snow load design standards for such temporary structures provided an alternate means to mitigate snow loads has been provided.

(Code 1990, § 15.24.130; Ord. No. 13-10, § 3(exh. A), 12-4-2013; Ord. No. 19-05, § 2(exh. A), 11-20-2019)