Where smoke alarms are required (IRC R314)
- In every sleeping room.
- Outside each separate sleeping area, in the immediate vicinity of the bedrooms (usually the hallway).
- On every story, including basements and habitable attics — not crawl spaces or uninhabitable attics.
- In split-levels, rules allow one alarm to cover an adjacent lower level less than a full story below in some cases.
Where CO alarms are required (IRC R315)
Carbon monoxide alarms are required when the house has a fuel-fired appliance (gas furnace, water heater, range, fireplace) or an attached garage with an opening into the house.
- Outside each separate sleeping area, in the immediate vicinity of the bedrooms.
- Inside a bedroom if a fuel-burning appliance is in the bedroom or its attached bathroom.
Combination smoke/CO alarms are allowed and are the easiest way to satisfy both rules in the hallway. Some states require CO alarms more broadly — check local amendments.
Power and interconnection
| Requirement | New construction (typical) |
|---|---|
| Power | Hardwired to the building wiring with battery backup |
| Interconnection | All smoke alarms interconnected so one sounds them all (wired or listed wireless) |
| Listing | Listed to the applicable UL standards |
Plan checkers frequently ask for a note stating that alarms are “hardwired with battery backup and interconnected.”
Placement mistakes to avoid
- Too close to bathrooms — code keeps smoke alarms a set distance (commonly 3 feet) from the door of a bathroom with a tub or shower to avoid steam false alarms.
- Too close to cooking appliances — minimum distances apply, and photoelectric alarms are allowed closer than ionization types.
- Dead air spaces — near the peak of vaulted ceilings or at wall/ceiling corners, per manufacturer instructions.
- Forgetting the basement or bonus room — every habitable level needs one.
Net clear opening, sill height and window well rules — the other life-safety comment plan checkers send most.
Read the guideHow to show alarms on permit drawings
- Place symbols on the floor plan or electrical plan: SD (smoke), CO, or SD/CO (combination).
- Include a legend defining each symbol.
- Add the general note: hardwired, battery backup, interconnected, listed.
- Show every level, including basements.
If your correction letter says “Show smoke and CO alarm locations,” this is usually a quick drafting fix. Our Permit Correction Service handles it along with every other drafting comment for $499 flat.
Additions and remodels
When you add bedrooms or do work that requires a permit, many jurisdictions require the whole house to be brought up to current smoke and CO alarm rules — not just the new space. Exceptions often apply where walls and ceilings aren't opened (e.g. battery or wireless interconnected alarms allowed). Adding a bedroom? See how to add a bedroom to a house plan.
Frequently asked questions
Where are smoke detectors required in a new house?
In every bedroom, outside each separate sleeping area, and on every story including basements and habitable attics, per IRC R314 as adopted locally.
Are CO detectors required if my house is all-electric?
Under the IRC, CO alarms are required when there are fuel-fired appliances or an attached garage with an opening into the house. An all-electric house with a detached garage may not need them, but some states require them anyway.
Do smoke alarms need to be hardwired?
In new construction they are typically hardwired with battery backup and interconnected so all alarms sound together.
Can I use combination smoke/CO alarms?
Yes. Listed combination alarms are commonly allowed and simplify hallway placement.
Can you add alarm locations to my permit drawings?
Yes. We add smoke and CO locations, legend and notes as part of our $499 Permit Correction Service.