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I need to place a smoke alarm on my first floor (no sleeping areas). There is a wall portal with a 15" lintel (see image) between the living room and the dining room.

I am unsure whether one alarm is adequate for both of these areas. My understanding is that smoke in either of these areas would tend to hug the ceiling and therefore, I would think that there would have to be a lot of smoke before it would begin to dip below the lintel into the other area. Assuming only one alarm in either area, my concern is that this could significantly delay the alarm. So, I wonder if the right solution is to install an alarm in each of these areas.

In the event of a fire, would enough smoke be in the air to trigger an alarm in either area or would the lintel tend to localize the smoke to one area and thus delay the alarm?

Portal between living/dining rooms

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    Install in both, absolutely, and thank you for asking this question. – Mast Jan 2 at 14:34
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    Something to consider here is false positives. I have a similar situation to the one you pose: One one side a kitchen, the other side a living room and a hallway to the sleeping areas. When I cook (see: set food on fire), it barely takes much smoke to set off the ionization smoke detector in the hallway. If you go with two, consider mixing and matching ionization smoke detectors and photoelectric as each responds better to different types of fires if you are going with two in close proximity. – statueuphemism Jan 3 at 16:05
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Yes and fantastic question, the lintel/header/apron will absolutely delay detection...by quite a lot. Therefore, I absolutely agree with Jack that you need to place the detector closer (the lintel side that's closer to the threat) to the known threat area or even just within the shortest path from that area. Which, may not involve this lintel nor these rooms.

An abundance of appliances is always your biggest culprit indicator, not that a TV or outlet's wiring could be faulty... though they would've typically revealed themselves with early symptoms.

I would suggest either a ceiling placement of the detector or a high wall placement that results in the detector being very close to the crown molding. The ceiling will fill with smoke long before it escapes beneath the lintel/header/apron.

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  • I mentioned in a comment to Jack that the dining room door connecting to the kitchen is closed at night, leaving the living/dining areas closed off from the kitchen-type risks. There's nothing but furniture in the dining room and just TV/entertainment electronics in the living room. We do sometimes have a candle in the living room. So the risk in these areas is low but not zero, and it seems I should address it. – Darryl Jan 2 at 5:57
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The Code (See ICC R314) requires a smoke alarm located:

  1. In each sleeping room.

  2. Outside each sleeping room area in the immediate vicinity of the bedrooms.

  3. On each additional story, including a basement, but not uninhabited attics and crawl spaces.

Also, when one alarm is activated, the others shall sound an alarm. However, in remodel and retrofit projects, this requirement is not required.

In general, the detector shall be located at the highest point in the room or within 12” of the highest point. If your lintel is 15” deep, you can see that an additional detector would certainly help. Remember, detectors are installed for “early detection”. Anything you can do to assist that early detection will help.

(How about carbon monoxide detector?)

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  • Thanks, @Lee Sam, early detection is what I was thinking. BTW I am using Nest Protects, so that covers both CO and interconnection. – Darryl Jan 2 at 5:20
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Where would a potential smoke source be coming from? The direction of the Dining Room or the Living Room? Both ceilings could have a smoke detector, but if a fire only has a possibility of starting by itself in one area, no need for 2 alarms

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  • There is no obvious (no fireplaces) source in either room, other than the unexpected (electrical, candle, accidents, etc). – Darryl Jan 1 at 22:58
  • Then if the kitchen is on the dining room side, I would put it in the dining room. As long as there a header between the kitchen and dining room, otherwise the alarm would be going off a lot. I believe the building code requires one there anyway as @Lee Sam has posted – Jack Jan 2 at 2:04
  • The kitchen/family room does connect to the dining room via a regular door (which is visible in the image). I left this info out to simplify the question, but the kitchen/family doors are closed at night (pets). Therefore, I have a smoke detector in the family room. This is what led me to figure I needed another in the living/dining areas since smoke in those areas would be prevented from triggering the family room alarm by the closed doors. – Darryl Jan 2 at 5:40
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Quoting https://www.nfpa.org/News-and-Research/Publications-and-media/NFPA-Journal/2017/January-February-2017/In-Compliance/NFPA-72

If the depth of wall section above the door is 24 inches or less, for example, the code requires one ceiling-mounted smoke detector on one side of the doorway only. If the designer specifies the use of wall-mounted detectors, then the code requires two detectors, one on each side of the doorway.

Though the above is referring to smoke-detector automatic closing fire doors.

My gut feeling is that two detectors is a good solution. I'd position them in the middle of each room, not on the wall above the door. "why not both?"

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