I'm planning to install recessed lighting (GU - 50W, 8 of them) in the
ceiling of a flat roof extension (the ceiling is 12'x18' approx,
200mm joists). The ceiling is to be insulated with Celotex (140mm),
but I'm told by Celotex that you should not install recessed lights in
a ceiling insulated with Celotex ! The main reasons they give are that
it compromises the U value of the roof, since you have to cut holes in
the celotex to accomodate the recessed fitting.
I looked at fire-caps to sit over the recessed lights - they help with
heat loss and noise, and of course stop potential fires getting into
the ceiling too quickly - but again the fire-cap people suggest not to
put recessed lights into a Celotex insulated ceiling.
Help ! I see plenty of programs/articles where people have recessed
lights in flat roof ceilings - how do they do it ? Do they use Celotex
? How big are the holes they cut in the Celotex ? Do they use
something else to insulate the ceiling ? Do you use fire-caps ?
Any ideas much appreciated.
Well, it's rather a strange thing you seem to be doing. On one hand,
trying to insulate your house to conserve energy, and on the other
hand using such inefficient lighting you've got loads of waste energy
to dump through your house insulation ;-).
Some of them burn down their houses -- seriously. Celotex may not
burn well itself, but in a fire I suspect it will give off loads of
cyanide, pretty much guaranteeing you won't get out. I would want
a good fireproof/heatproof barrier between any cellotex and possible
ignition sources. I wouldn't dream of putting recessed 50W spotlamps
anywhere near the stuff. If you do, at least make sure you use GU10's,
(aluminised) and not GZ10's (dichroic -- cool beam -- which will dump
even more heat into the ceiling). I would have suggested low voltage,
but I don't think aluminised LV reflector lamps are available any more;
I only see dichroic ones. Personally, I wouldn't dream of using large
numbers of downlights for general lighting. They are more appropriate
to task and accent lighting.
Well, I have done similar.
here are some real world facts.
Celotex DOES burn, but does not sustain the reaction. I.e. its not
exothermic. It DOES produce a lot of nasty fumes. Cyanide is not one of
them tho. I know cuase I have whoffed cyanide in teh chem lab. However I
would not care to fill my lungsd with the smoke that coes of celotex
when you stick it in a fire. It needs to be almost red hot to do it mind.
I have loads of 50W LV's for general lighting in my ceilings. Some are
near celotex. The rest are near rockwool. Proividd you leave a few
inches around the,m and make sure they are not near combustble material
(right alonsgide joists) and ensure that no combustile materail *thatch,
birds nets etc) can drop onto them, they are fine. The best solution I
heard here was put an inverted flowerpot over the top Lets face it they
have PVC covered wire feeding them, and that burns well...so its no big
I jave mine manly in rockwool, with the insulation pushed back, and the
joists covered with chipboard. The chip is warm but not hot above them
-0 6" from ceiling.
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