Cant find a common agreement on insulation & down lights....

[Rodders66]

For clarity..

It's a mono pitch roof and the vents are over facia strips along the full ength.

Cheers
All

 

[john4703]

How big a problem is it to cover LED lights with insulation? Don't all shout at me but I was wondering if simply pushing the insulation up would really be a problem as LEDs are such low power that they don't produce much heat.
A problem might be if someone replaced LED lamps with another type that did produce a lot of heat.
I wonder if the regulations have not caught up with low powered LED lamps.

 

[StephenStephen]

You might have thought of this already, but just in case... I put in LED strips in a new room last year and have been amazed at the huge amount of light they produce, and the even spread of light as well - I rarely switch them on unless I have some heavy duty interrogation to do, and warn people before doing so. I'm just thinking that this would would be quicker, simpler, easier to maintain and prevents all the complexities and problems of making holes in your ceiling.

 

[ban-all-sheds]

How big a problem is it to cover LED lights with insulation? Don't all shout at me but I was wondering if simply pushing the insulation up would really be a problem as LEDs are such low power that they don't produce much heat.

They don't.

But they are extremely intolerant of what little they do create as they have a negative temperature coefficient of resistance, and can very easily go into thermal runaway.

 

[SimonH2]

The roof is vented, so in principle there's a void above the insulation and moisture shouldn't be an issue I believe...but maybe that's not correct?
Or are you suggesting that the moisture would be inside the pockets I make within the insulation?

The problem is that you'll have cold spots on your ceiling, there will be condensation on these cold spots, and so the surface (paint first, then plaster, etc) will get damp. If the house is VERY dry then it might not be a problem, but at the other extreme you find yourself with mouldy patches round the light

But they are extremely intolerant of what little they do create as they have a negative temperature coefficient of resistance, and can very easily go into thermal runaway.

While that is true, even half decent assemblies will have some form of current control - and most will have constant current drivers. However, they are quite sensitive to temperature - both the LED chip itself, and the driver electronics. As you say, while they generate little heat - they depend on that heat being able to get away.
I've seen (on the gogglebox) a demonstration of making an oven from insulation with nothing but a light bulb in it - and then cooking a chicken to prove it actually works. Burying an LED fitting in insulation would achieve the same effect - the heat builds up because it can't get away, and something fails when it gets too hot.
And with a work hat on, I've had people ask why they can't put the noisy computers in <typically some small unventilated cupboard>. They then think I'm stringing them some bull manure as I try to explain that the nice cool cupboard won't stay nice and cool once they put what is effectively a fan heater into it

 

[Rodders66]

Thanks Simon.

Do you think that the minimum 50mm Celotex, I'd have 'above' the fitting (but approx 25mm away from it) would still make it 'cold'?...I was thinking it would be partly insulated and the fact that the entire roof being open to atmosphere and with airflow would result in no moisture / condensation?

I understand the point with a chamber being made with a nice warm fitting in it, but don't they sell and allow (LBC) the use of fire rated 'caps' to be used on down-lighters especially in combination with fibre insulation?

 

[SimonH2]

Just because someone sells something, doesn't mean it's allowed/sensible to use it in a specific situation.
A common use for hoods is to simply hold the fibre insulation up off the fitting - so you look in the loft and there's a "hump" in the insulation, but the insulation is the same thickness. Where fire rated ones are needed, it's likely to be between floors where the insulation needed is not as thick as the depth of the joists - so there a good chance that the insulation can still fit between top of cap and the top of the space.

The open to atmosphere part of your roof is the cold side - and this isn't where you are concerned about the condensation (at least in this context). The condensation you are concerned about is in one (or both) of :

• The ceiling itself, where it's colder than the rest and so gets damp.
• The void behind where if you aren't careful with choice of fitting and correct installation (don't underestimate the general ignorance level amongst trades here) you can get moist air getting past the vapour barrier. This can then condense, wet the insulation which then has less insulating properties and makes the cold problem worse.

You are correct that 50mm of Celotex is going to give you significant insulation. Looking back you will have 150mm total - so for these 12 locations you will have just one third of the insulation, roughly 3 times the heat loss.

Finally, yes the lights will warm this space - when they are switched on. For the rest of the time, it will be cold.