I'm having a moan. Celotex and downlights.

[electromonkey]

I've been called up to start my second fix for a re wire I started a few weeks ago. The customer is project managing the re firb of his house and has opted to insulate every possible inch of space throughout his 3 story house. He ordered a load of Celotex as per building regs for his loft conversion and was given a surplus amount so has used it throughout the house. In stud walls and under floor boards etc. He is having downlights throughout the property and much to my horror, absolutely no space has been left for me to pop the DL's up. The only way I can see getting around this is by putting my hand in through the hole cut for the DL's and clawing at the celotex to rip it out. I have 37 to do. :-(

Anyone had a similar problem before? If so, any tips?

Cheers

 

[Paul.M]

I had the same problem last year, insurance job. The apartment above had a leak whilst away on holiday and the ceiling had to be ripped down and replaced. Told the home owner not to let the plasterer to put insulation where the lights are going. Did he take any notice? Not a chance. Customer not happy about all the dust I was making pulling the stuff out but what else can you do? I only had 8 to do not 37!!! Itchy stuff, wear long sleeves, goggles, mask and gloves, saves you itching and scratching all day long.

 

[MarkieSparkie]

I've not had this problem yet. However, be aware you will need to assure yourself that all installed cables that have PVC insulation are not in contact with the Celotex, because Celotex causes the PVC to leach its plasticiser. This makes the cable migrate/melt into the Celotex causing yet more plasticiser to leach as well as reducing the current carrying capacity due to being now surrounded by thermal insulation. The leaching of plasticiser also cause the cable to rapidly age harden and become brittle.:32:

 

[Sparky Ninja]

Padsaw in at an angle?
I'd ask if Mr plasterer would like to come and give you a hand.

I'd be looking at charging extra with that quantity of bulls ups.

 

[electromonkey]

Cheers guys,

£30 an hour for cutting celotex it is then. It'll take him a while to earn that back on his reduced heating bills!

That'll learn him!

 

[electromonkey]

I've not had this problem yet. However, be aware you will need to assure yourself that all installed cables that have PVC insulation are not in contact with the Celotex, because Celotex causes the PVC to leach its plasticiser. This makes the cable migrate/melt into the Celotex causing yet more plasticiser to leach as well as reducing the current carrying capacity due to being now surrounded by thermal insulation. The leaching of plasticiser also cause the cable to rapidly age harden and become brittle.:32:

It's the foil backed stuff so is that likely to have an impact too?

 

[robsparky1975]

amazing how stupid people can be to fill things where they know lights are going,donkeys,and i wont tell you about the 200+ downlights that the cables were left above double thick plasterboard,some people were not happy when i had to make loads of 4" holes to pop my arm up and find cables,why do these people want to irritate us,it costs them in the long run.

 

[sythai]

I've been stitched like this before.... about 30 of them.... celotex, plastered and painted - urgggh!

Padsaw in at an angle?

.... or hack saw blade (out of the saw)

 

[telectrix]

or borrow the plumber's blowlamp.

 

[chris@expert]

I've checked this with Celotex (the manufacturer) and they told me that you're not supposed to cut into it. Celotex has got to remain vapor proof.

This poses an obvious problem when installing recessed downlights, they recommend installing wooden battens at the side of the downlights to raise the Celotex over it. Here is a diagram below...


Or you could install surface mounted downlights instead?

 

[Deleted member 26818]

Do they give a minimum size to allow for an air gap for heat disapation, or is that something you have to determine from the light fitting manufacturer's?

 

[telectrix]

think a rule of thumb is 50mm all round and 100mm above. suppose you could reduce that for LEDs, but what's to stop halogens being retro fitted? the insulate everything brigade should all be shot.

 

[shagbite]

i think the house has probably burned down by now.

 

[chris@expert]

The lighting manufacturers don't usually have an answer to this. The downlight in my diagram is an integrated LED downlight, the LED is built into the downlight so no chance it could be replaced with a hot halogen.

The only other issue is ventilation for the LED. Will it get enough air circulation from within the ceiling void? If not if could reduce the life expectancy. The ZEP1 downlight in the diagram is a very cool running one with a good quality heat sink.

 

[telectrix]

i think the house has probably burned down by now.

well at least the insulation should keep the heat in over xmas.