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Topic # 151178 16-Aug-2014 16:08
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I've bought two smoke detectors to improve the coverage in our house.  Trouble is, I'm not sure where is the best place to mount them.  I've looked at the Fire.org.nz website, which is helpful, but I'm still not sure with our particular ceilings.



Which is safer/better - mounting the smoke detector on the exposed rafter, or on the plaster in between the rafters?  From what I could make out online, there is potential for dead air between rafters, though these beams are quite as deep as some of the ones that were used in other examples.

Alternatively, what about mounting it on the wall?  I've seen advice that suggests mounting it between 300mm and 500mm from the ceiling line, which would make it a little easier to silence in the event of a false alarm (especially for my wife, who is shorter than I am).

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  Reply # 1109538 16-Aug-2014 16:17
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At 30-50mm the wall should be OK, though since your getting them to improve coverage I'd say ON the beams myself, allowing more central placement overall ?



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  Reply # 1109539 16-Aug-2014 16:19
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Forgot to say, these smoke detectors are going in bedrooms.  We already have one in the hallway, and will be getting a couple more for the two lounges.

 
 
 
 


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  Reply # 1109602 16-Aug-2014 18:55
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I have worked with fire safety equipment for 12 years now. I would say avoid putting smoke detectors on the walls, and make sure they are always at least 50 cm out from any wall or beam. Middle of the roof is a good place to have them.

Another thing you might want to consider to be safe is to make sure your smoke detectors are photo electric and not ionization. The Photo electric smoke detectors are able to much quicker alarm you on smoldering fire smoke, but also work good on open fire smoke. While the ionization smoke detectors only are able to warn you about open fire smoke.

You can tell the difference by looking after the typical fan mark on the back (the warning for radiation sign). Only the ionization smoke detectors have that sign on them.






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  Reply # 1109608 16-Aug-2014 19:10
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Thanks for the reply. They are photoelectric long life (10 yr battery) alarms. Would you recommend installing the alarm on the beam, or on the plaster in between the beams?

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  Reply # 1109618 16-Aug-2014 19:23
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You may also want to check with the building inspectors at your local city office.
In hastings, for new house builds, you are required to have a smoke detector in the hallway no further than 2 metres from any bedroom door.
I know your putting them in bedrooms, but the local building regulations would be a good guide to start with when looking for suggestions.

Also the higher they are, the better they will respond in a home. So if your beams protrude more than ~1cm below the plaster then perhaps the plaster being higher would be better as it may give you a few extra seconds.




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  Reply # 1109619 16-Aug-2014 19:23
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If the ceiling is poorly insulated then put them at the top of the wall, as a cold smoke detector in a warm room is more likly to false alarm from humidity.




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  Reply # 1109714 16-Aug-2014 22:46
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richms: If the ceiling is poorly insulated then put them at the top of the wall, as a cold smoke detector in a warm room is more likly to false alarm from humidity.


Never on the top of the wall. Never close to a wall. The reason is that there is very little airflow close to walls/portrutions.

I get that you want to make sure the smoke detector does not cool down and thereby get condensation, because you do get false alarms from that. But having a smoke detector in a place with little airflow is about as bad as not having one at all.

If you are going to place it on the wall (Which, if its an outside wall or a wall to a cold room, also could be a possible condensation problem), you need to make sure that its down at least 30 cms from the top of the ceiling. See: http://www.nfpa.org/safety-information/for-consumers/fire-and-safety-equipment/smoke-alarms/installing-and-maintaining-smoke-alarms for more info.




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  Reply # 1109815 17-Aug-2014 10:22
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The DBH Building Code regulations are here.

"On or near" the ceiling is specified.
It also states that the alarms shall have a test facility "easily reached" by the building occupants.
"Near" and "easily reached" aren't further defined.  When I installed alarms in our house, I installed them on the walls about 150mm down from the celiings.  These were required for building consent, and were inspected/tested and approved.  While "on" the ceiling might give better detection performance, if they can't be easily reached (ie without getting a stepladder or chair), then the chance of them not being tested routinely as specified increases.  There are plenty of cases of house fire where detectors fail because they've been disabled due to false alarm / poor location, or because they're not easily accessible, they're never maintained.  Monthly testing and 6 monthly cleaning seems to be recommended - but I expect this seldom happens.

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  Reply # 1109816 17-Aug-2014 10:26
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jarledb: 
If you are going to place it on the wall (Which, if its an outside wall or a wall to a cold room, also could be a possible condensation problem), you need to make sure that its down at least 30 cms from the top of the ceiling. See: http://www.nfpa.org/safety-information/for-consumers/fire-and-safety-equipment/smoke-alarms/installing-and-maintaining-smoke-alarms for more info.


To quote from the article you linked to:
Wall-mounted alarms should be installed not more than 12 inches away from the ceiling (to the top of the alarm).



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  Reply # 1109825 17-Aug-2014 10:44
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jarledb: 

Never on the top of the wall. Never close to a wall. The reason is that there is very little airflow close to walls/portrutions.

I get that you want to make sure the smoke detector does not cool down and thereby get condensation, because you do get false alarms from that. But having a smoke detector in a place with little airflow is about as bad as not having one at all.

If you are going to place it on the wall (Which, if its an outside wall or a wall to a cold room, also could be a possible condensation problem), you need to make sure that its down at least 30 cms from the top of the ceiling. See: http://www.nfpa.org/safety-information/for-consumers/fire-and-safety-equipment/smoke-alarms/installing-and-maintaining-smoke-alarms for more info.


The wall isn't my first choice.  I think it would be better on the ceiling.  

But my principal concern is whether it's better to mount them on the wooden rafters or on the plaster (see photo in my original post above).  To give some scale to the picture, the central beam is about 160mm deep, while the cross beams are 90mm deep.  There is 560mm space between each cross beam.  

I think I'd prefer to mount it on the central beam, but I'm worried that it wouldn't detect smoke as effectively as if it was on the plaster, then I would mount it directly onto the plaster.  However, if I mount it in the centre of one of the plaster panels, then it would be about 280mm away from 90mm-deep beams on either side, which seems to be too close to a protusion (potential dead air).  So my main problem is whether the beam or the plaster is the better position.

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  Reply # 1109914 17-Aug-2014 13:45
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Lizard1977:  But my principal concern is whether it's better to mount them on the wooden rafters or on the plaster (see photo in my original post above).  To give some scale to the picture, the central beam is about 160mm deep, while the cross beams are 90mm deep.  There is 560mm space between each cross beam.


Then install 2.  Or borrow a fog machine and see where the most smoke goes.




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