Restaurant Conversion: Hood, Makeup Air, and What Comes Out of the Kitchen

The Type I hood is correct; everything downstream of it is not.

• Hood. Deep-fat frying and charbroiling produce grease- and smoke-laden vapors, so a Type I hood is required over those appliances. That part of the design is right.
• Duct construction. Grease ducts must be of the minimum thickness and construction the code specifies, continuous and liquid-tight, supported at the required intervals, with the required clearance to combustibles - or enclosed in a listed grease duct assembly where the clearance cannot be maintained. Single-wall galvanized duct run loose through a concealed ceiling space generally does not satisfy this.
• Enclosure. Where a grease duct passes through a concealed space or a rated assembly, the code requires an enclosure of a specified fire-resistance rating or a listed factory-built duct enclosure. The claim that sprinklers in the ceiling waive the clearance or enclosure is wrong; sprinklers do not substitute for duct protection.
• Discharge location. The termination must meet the code's criteria for height above the roof relative to nearby construction, and for distance from property lines, operable openings and outdoor air intakes. Eight feet from a property line and six feet from an intake serving other tenants are almost certainly noncompliant, and even where a dimension passes, discharging grease-laden air into an intake is a nuisance and re-entrainment problem the official can require corrected.
• Access and cleaning. The duct needs access panels at the required locations for cleaning, and the hood requires the listed grease filters, a grease cup, and clearance from cooking surfaces.

Result: redesign the duct and the termination; the hood itself stays.

A commercial kitchen exhaust without makeup air turns the building into a vacuum cleaner, and the code requires the balance to be designed.

• Makeup air. Commercial kitchen exhaust systems must be provided with makeup air in the quantity the code requires (generally equal to the exhaust, with the allowances and exceptions the adopted edition contains). A storefront door is not a designed air supply, and the existing rooftop unit is not sized for the hood exhaust.
• Pressure effects. A 10-ft Type I hood exhausting several thousand cfm will depressurize the space. The visible symptoms are doors that will not open, whistle, or slam, and the invisible one is backdrafting of natural-draft appliances.
• Combustion air. The gas-fired appliances in the building - including the water heater and any furnace sharing the space or a closet open to it - must be provided combustion air in accordance with their listing and the fuel gas provisions. Combustion air cannot be drawn from a space that is being driven negative by a kitchen exhaust. If the appliances backdraft, the fix is not a CO alarm; it is a corrected air balance.
• Design outcome. Provide a dedicated tempered makeup air unit interlocked with the exhaust fans, verify combustion air for each appliance, and verify that the building's other exhaust systems remain balanced. In many jurisdictions the energy code also requires demand-controlled ventilation for the hood, which affects the design.

Official's action: the mechanical permit cannot be approved without a makeup air design and a combustion air analysis.

Grease interceptor:

• The plumbing code requires a grease interceptor or automatic grease removal device for food-processing establishments where fats, oils and grease are introduced into the drainage system. A restaurant kitchen qualifies. The absence of a proposed interceptor is a deficiency on its face.
• Sizing must follow the code's method or an approved engineering calculation, and the device must be accessible for cleaning and maintenance, installed where the code requires relative to the fixtures and other connections.
• The existing 4-inch building drain must be re-evaluated for the new fixture load and venting. An existing drain serving a former retail tenant tells you nothing about restaurant loads. Local sewer authorities often impose stricter requirements than the code; verify before approval.

Toilet rooms:

• Required fixtures are computed from the fixture-ratio table for A-2 occupancies, by sex, plus lavatories, using the 110-occupant load. A single water closet, without more, will not satisfy the count for both men and women at that occupant load. Do the arithmetic and show it, because the ratio varies by edition.
• A single-occupant toilet room may be counted for either sex where the code permits it, but that allowance does not multiply a single fixture into the number the table requires.
• Because this is new work in a change of occupancy, the new and altered toilet rooms must be accessible: clear floor space, grab bar blocking and installation, door clear width and swing, lavatory height and knee clearance, and the required signage. A 1960s toilet room will almost never pass without reconstruction.
• Employee facilities must also be addressed; they cannot be waived by sending staff to a public restroom that does not exist.

Action: require a revised plumbing plan with a sized, accessible grease interceptor, the fixture count calculation by sex, and accessible toilet room details.