SOURCE: Chief Appraiser Knowledge Base — Carbon Monoxide Detector Requirements Near Attached Garages and Fuel-Burning Appliances Compiled from: 2024 International Residential Code Section R315 (model code); Nevada Revised Statutes Chapter 477 (State Fire Marshal authority); Nevada Administrative Code Chapter 477; local jurisdiction fire code amendments (e.g. Southern Nevada Amendments to the International Fire Code); UL 2034 (carbon monoxide alarm listing standard); HUD Single Family Housing Policy Handbook 4000.1 (appraiser verification standard) Last reviewed: August 2026 ===================================================================== Carbon Monoxide Detector Requirements Near Attached Garages Carbon monoxide poisoning is a genuine, recurring cause of injury and death in homes with an attached garage or a fuel-fired appliance, which is why carbon monoxide alarms are one of the more consistently enforced life-safety items in modern residential construction. Unlike smoke detectors, which have a single long-standing national model code history, carbon monoxide alarm requirements are newer and are primarily driven by model building codes that individual states and local jurisdictions choose to adopt, rather than by a single nationwide federal statute. The model code standard: International Residential Code Section R315. The 2024 International Residential Code, Section R315, is the model code provision most states and local jurisdictions use as the basis for their own carbon monoxide alarm requirements. Under this model code framework, a dwelling unit is required to have carbon monoxide alarms where either or both of two conditions exist: the dwelling unit contains a fuel-fired appliance, such as a gas furnace, gas water heater, gas range, gas fireplace, or wood stove, or the dwelling unit has an attached garage with an opening that communicates with the dwelling unit, meaning a door, duct, or other opening that connects the garage to the living space rather than a garage that is fully separated with no connecting opening at all. Where alterations, repairs, or additions requiring a permit occur to an existing dwelling, the model code framework generally requires the dwelling to be brought up to the same carbon monoxide alarm standard as new construction, not just the specific room or system being altered. Carbon monoxide alarms under this framework are typically required to be interconnected with the dwelling's smoke alarms, to receive their primary power from the building wiring, and to have battery backup so they continue to function during a power outage. The actual alarm devices themselves are expected to be listed to UL 2034, the Underwriters Laboratories standard for carbon monoxide alarms, which governs sensitivity, alarm threshold, and device reliability testing. Why this is a model code matter rather than a single nationwide law. The International Residential Code is published by the International Code Council, a private code-development organization, and by itself has no legal force anywhere. It only becomes enforceable law once a state legislature, state agency, or local jurisdiction formally adopts a particular edition, often with local amendments. This means the exact carbon monoxide alarm requirement that applies to a given property depends on which code edition that property's state or local jurisdiction has adopted, and what amendments that jurisdiction made to the model language, not on the model code text itself. Nevada's adoption pattern. Nevada does not have a single statewide statute that independently mandates carbon monoxide alarms in every residential occupancy category the way some states do. Instead, Nevada Revised Statutes Chapter 477 gives the State Fire Marshal general authority over fire prevention code adoption and enforcement, and the practical carbon monoxide alarm requirement that applies to a given Nevada property is most often supplied through that property's local jurisdiction adopting International Residential Code Section R315 language, sometimes with its own local amendments layered on top, such as the Southern Nevada Amendments adopted for the Las Vegas metropolitan area. This means a Nevada appraiser or real estate agent should confirm the governing code edition and any local amendments with the specific city or county authority having jurisdiction over the subject property, rather than assuming one statewide rule applies everywhere in the state. Why carbon monoxide specifically, and why attached garages matter. Carbon monoxide is colorless, odorless, and non-irritating, which is exactly why it is so much more dangerous than a fire or gas leak that a person can see, smell, or hear before it becomes deadly. A running vehicle left idling in an attached garage, a malfunctioning gas furnace or water heater, or a blocked flue can all produce carbon monoxide that migrates from the garage or the appliance closet directly into living space through any communicating opening, including a door, an unsealed duct penetration, or shared framing cavities that were not properly air-sealed during construction or a later remodel. This is the specific mechanism the model code's "attached garage with a communicating opening" trigger is written to address, separately from the more familiar fuel-fired-appliance trigger. A detached garage with no shared wall or connecting opening to the dwelling does not create the same exposure pathway and is treated differently under the model code framework than a garage that shares a wall, ceiling, or door with the living space. What this means for appraisers. FHA and VA appraisal guidance does not set its own independent carbon monoxide alarm standard separate from state and local code; rather, it generally directs the appraiser to confirm that life-safety items such as smoke alarms and carbon monoxide alarms required by the applicable local code are present and appear functional at the time of inspection, since these items fall within the general minimum property requirement that a property be safe, sound, and sanitary. An appraiser is not expected to be the authority on which specific code edition a given city or county has adopted, but should note the presence or clear absence of carbon monoxide alarms in an attached-garage or fuel-appliance dwelling as part of the overall condition observations, and flag it for further verification against local code where its absence appears to be a genuine safety deficiency rather than a cosmetic omission. Distinguishing carbon monoxide alarms from smoke alarms. Smoke alarms and carbon monoxide alarms are frequently required together and are often sold as a single combination unit, but they are not interchangeable and a smoke alarm alone does not satisfy a carbon monoxide alarm requirement, or the reverse. Smoke alarm placement and quantity requirements have a much longer, more uniform national history across model codes and are typically required in every bedroom, outside every sleeping area, and on every level of a dwelling regardless of whether the dwelling has an attached garage or fuel-fired appliance at all. Carbon monoxide alarm placement is narrower and condition-triggered: it depends specifically on the presence of a fuel-fired appliance or an attached garage with a communicating opening, and where required is typically placed outside each separate sleeping area rather than inside every individual bedroom. A property inspection or appraisal observation noting "smoke detectors present" should not be read as also confirming carbon monoxide alarms are present, since they are frequently checked and documented as two distinct line items even when combination units satisfy both requirements simultaneously. What this means for real estate agents preparing a listing. A seller with an attached garage, a gas furnace, a gas water heater, a gas range, or a gas fireplace should have working carbon monoxide alarms installed before a buyer's inspection or the appraiser's visit, both because it is very likely required by the local code that actually governs the property and because a missing carbon monoxide alarm is an easy, low-cost item to flag as a potential repair condition that can otherwise slow down or complicate a closing. Unlike some appraisal line items that require a licensed contractor to resolve, installing a listed carbon monoxide alarm is inexpensive and can typically be handled by the seller directly before the appraisal appointment, similar to the water heater strap and smoke detector items already covered in the Garage and Fire Safety section of this library. Practical checklist. Confirm whether the dwelling has a fuel-fired appliance or an attached garage with a communicating opening to the living space, since either condition typically triggers the carbon monoxide alarm requirement under the model code framework. Confirm carbon monoxide alarms are installed, listed to UL 2034, and appear to be interconnected with smoke alarms where the local code requires interconnection. Confirm the alarms have power, whether hardwired with battery backup or a sealed long-life battery unit, and are not past their manufacturer-specified replacement date, since carbon monoxide sensors have a limited useful life unlike a simple electrical device. Confirm the governing code edition and any local amendments with the city or county authority having jurisdiction, rather than assuming a single statewide Nevada rule, since Nevada's own requirement flows through local adoption rather than one standalone state statute, so always confirm with the local jurisdiction rather than assuming one statewide rule applies.