Down Lights in Celotex

[Midwest]

Know this has been debated before, but I'm getting a bit peeved.

Talking of downlights installed in vaulted ceilings, insulated with Celotex or Kingspan. Without ceiling being designed to have a false void to install said down lights, as far as I'm aware there's no way of pyhsically installing downlights without cutting holes into Celotex, which reduce u-value and can create damp in ceiling void.

Last time I checked with my LBC, this was a big no no for them, and they wouldn't pass off building work with such an installation. Celotex & Kingspan say the same. So that's what I've always said when customers have asked for such.

I've just been to quote a job in a property, with a recently finished extension, with a vaulted ceiling full of downlights. Am I missing some recent developments, or are people just going ahead regardless?

 

[danzor]

I do not miss the days of cutting down lights into celotex, its like the modern version of asbestos

 

[markc123]

Would love to be proven wrong, but don't think you're missing anything mate.

Has said extension had normal lights installed to pass building then paper trail-less down lights installed separately at a later date?

 

[Richard Burns]

People are just going ahead regardless, as usual.
How they get past BC I do not know.
Though there are some very flat LED down lights out there now that do not need much space at all above them.

 

[Midwest]

Nope in this instance some cheapo tilt fittings , I won't fit them, but obviously some sparks are, downlights in insulation that is.

 

[Midwest]

Would love to be proven wrong, but don't think you're missing anything mate.

Has said extension had normal lights installed to pass building then paper trail-less down lights installed separately at a later date?

No house owner had downlights installed at time of building work, very pleased with them too. Didn't say anything, didn't want to rain on his parade.

 

[sparksburnout]

Interesting this. I have been involved in 3 instances where (LED) down-lights have been required in vaulted and flat roof extensions. One was for a local builder, I asked him to clarify the situation with building control before agreeing to get involved, BCO turned up on site and the 3 of us had a meeting, upshot was that because the roof had a vented space above the Celotex (as most if not all do) he was not concerned about condensation running back, and he considered that the U value of the extension as a whole would not be compromised to an extent where it would cause him a problem. He pointed out (probably wisely) that the 4 Velux windows would lower the value to an extent where the lights were not considered worrying about. On the other one I rang the BCO myself and he said the same thing and crack on. Both these were for two different areas. I also got partially involved in another job where the customer himself had fitted approx 40 (!) lights in a largish vaulted extension, and again BCO did not raise any objection. All 3 of these have been signed off by BC. Now, I know that the manufacturers state that down-lights should not be installed in Celotex, but I think this is for cold bridging in sealed applications, not in vented ones. Not sure if anything has changed recently, next time I get asked to do any more I will just contact BC again and see what they say. Maybe different areas have different rules??

 

[Midwest]

I've emailed my LBC, and have asked the question. I did ring and speak with them once before, when I was asked to install some and was categorically told NO. See what reply I get this time. I installed some DL in my own property in a vaulted ceiling some years ago. I asked my LBC if I could install them and as told no (my ceiling doesn't have a vented space, as far as I'm aware?), so I had a false void made to mount them in.

 

[sparksburnout]

I think their objection would be due to the non-vented roof. You would get condensation possibly building up, specially if they were those horrible nasty halogen ones, and possibly also heat considerations. There is no doubt fitting them will lower the overall U value of the roof, but is it worth worrying about? I am amazed at the (big) new houses that are being built round my way, with the seemingly fashionable massive windows running from floor to roof so you can see the entire hall/stairs/landing. Be a bloody shock for my neighbours if I lived in one I can tell you, never mind the U value.

 

[sam400]

Funny this should come up I am just having the same problem in a kitchen extension. The drawings spec a 35mm layer of celotex under the joists taped and sealed to provide a vapour membrane.
I said to the builder that it wasn't a good idea to drill big holes in for down lights, and he said he's done hundreds like it and its no problem.
Anyway I gave the local building control officer a ring and he recommended closing up the ceiling then building a false one underneath to house the down lights.
That went down like a lead balloon with the builder! Lol

i don't think we're friends anymore but at least the job will be done right!

 

[vxwestie]

I've done numberous installs where the BC haven't been too worried either.
Totally agree with the venting of the ceiling though, and LeD lights will create little or no heat.
Crack on, keep the builders and customers happy.
We're got enough to to worry about let alone U values when everything is so over specced these days too

 

[Midwest]

Interesting this. I have been involved in 3 instances where (LED) down-lights have been required in vaulted and flat roof extensions. One was for a local builder, I asked him to clarify the situation with building control before agreeing to get involved, BCO turned up on site and the 3 of us had a meeting, upshot was that because the roof had a vented space above the Celotex (as most if not all do) he was not concerned about condensation running back, and he considered that the U value of the extension as a whole would not be compromised to an extent where it would cause him a problem. He pointed out (probably wisely) that the 4 Velux windows would lower the value to an extent where the lights were not considered worrying about. On the other one I rang the BCO myself and he said the same thing and crack on. Both these were for two different areas. I also got partially involved in another job where the customer himself had fitted approx 40 (!) lights in a largish vaulted extension, and again BCO did not raise any objection. All 3 of these have been signed off by BC. Now, I know that the manufacturers state that down-lights should not be installed in Celotex, but I think this is for cold bridging in sealed applications, not in vented ones. Not sure if anything has changed recently, next time I get asked to do any more I will just contact BC again and see what they say. Maybe different areas have different rules??

Have my reply from my lbc, pretty much identical to yours;

You are quite right that fitting down-lighters in ceiling where the insulation is cut away does reduce the insulation in this element and I appreciate that for the fitting to have sufficient clearance around it this can mean removing an area considerably larger than the fitting. Ideally down-lighters would be anticipated early on in the project and the rafters would be deepened or battened to allow all the insulation and this void. However it is often a decision that comes later after the rafters have gone in.

To cater for this void one manufacturer fabricated metal boxes so the insulation can be cut around these but I have only seen them used once. What should happen in this isolated position where a down-light is proposed is that some insulation should be placed between rafters above the void required for the insulation. Again I know that this will reduce the insulation but if you consider a whole roof with roof windows the roof windows lessen the amount of insulation. For instance a typical roof may get a thermal value (U-value) of 0.18 (the lower the figure the better) a roof window may only have U-value 1.6. 25mm Celotex placed over a void for a down light U-value 0.7. As you can see it is far better than for a window. So it would be considered acceptable.

Where mineral wool is placed over a flat ceiling a box forming a void can be placed and all the insulation placed over.

I always advise there is some insulation over the down-light and that there is a void sized as required by the lighting manufacturer but I accept that I don’t get to see all works and if they are fitted retrospectively then there may be no control.


I've asked about the sealed void aspect, but haven't had a response on that. I've a customer who wants downlights in such a ceiling, he's going to ask advice of the BI, when he inspects the rafters etc.

 

[Midwest]

Have my reply from my lbc, pretty much identical to yours;

You are quite right that fitting down-lighters in ceiling where the insulation is cut away does reduce the insulation in this element and I appreciate that for the fitting to have sufficient clearance around it this can mean removing an area considerably larger than the fitting. Ideally down-lighters would be anticipated early on in the project and the rafters would be deepened or battened to allow all the insulation and this void. However it is often a decision that comes later after the rafters have gone in.

To cater for this void one manufacturer fabricated metal boxes so the insulation can be cut around these but I have only seen them used once. What should happen in this isolated position where a down-light is proposed is that some insulation should be placed between rafters above the void required for the insulation. Again I know that this will reduce the insulation but if you consider a whole roof with roof windows the roof windows lessen the amount of insulation. For instance a typical roof may get a thermal value (U-value) of 0.18 (the lower the figure the better) a roof window may only have U-value 1.6. 25mm Celotex placed over a void for a down light U-value 0.7. As you can see it is far better than for a window. So it would be considered acceptable.

Where mineral wool is placed over a flat ceiling a box forming a void can be placed and all the insulation placed over.

I always advise there is some insulation over the down-light and that there is a void sized as required by the lighting manufacturer but I accept that I don’t get to see all works and if they are fitted retrospectively then there may be no control.


I've asked about the sealed void aspect, but haven't had a response on that. I've a customer who wants downlights in such a ceiling, he's going to ask advice of the BI, when he inspects the rafters etc.

Give me strength, have a customer who wants downlights in his vaulted ceiling. Building Inspector (from same BC) said 'No'.

 

[sam400]

The kitchen extension I mentioned has had the insulation signed off by BC now,
I just got the builder to double batten over the celotex and then fix the plasterboard to the battens, I installed inceptor micros (49mm deep) into the void.
The celotex and vapour membrane remained intact, which is particularly important in this case as the ceiling void was un-vented, any breach in the vapour membrane would allow warm moist air into the ceiling void which would then condense on the cold roof, the condensation would have no where to go - surely not good?

sam

 

[telectrix]

you only get these condensation problems when all this bloody insulation goes in. same with blocking airbricks. houses need fresh air, not smothering in crap to save a few quid in gas bills.