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Topic Title: Downlights in pitched ceilings
Topic Summary: Dealing with kingspan
Created On: 05 January 2009 04:28 PM
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 05 January 2009 04:28 PM
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JZN

Posts: 559
Joined: 16 November 2006

Customer is having a single storey extension with a pitched roof. Internally, the ceiling will also be pitched with no flat surface (ie parallel to the floor) to fix lights to.

They want downlighters. Given that there will be celotex/kingspan type insulation beneath the plasterboard I'm thinking that there will be heat issues due to lack of space for heat to escape.

Has anyone else fitted recessed downlighters in this sort of ceiling? If so how did you go about it?

I've thought about LED downlighters but not sure if they will be light enough. Downlights with CFLs still seem to get pretty hot, although not as bad as halogens.

Thanks
John
 05 January 2009 05:47 PM
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gpaul2

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i had the same in december , what i did was to use fire rated downlighters and cut back all the celotex all the way back to the roofing felt and sraped away the sides of the celotex to allow for the heat to move around , i'll be just as worried about the loading on the cable passing through all that insulation , you'll have to de-rate the cable
 05 January 2009 05:58 PM
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JZN

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I'm beginning to think that it's going to be a monumental pain in the bum to get these installed. Must have taken you ages gpaul2 to cut back that celotex.

I guess i could get the builders to cut it out first, but downlights need pretty accurate placement otherwise they look a mess. There's also the issue of cutting the holes and finding the cables. Most plasterers don't like to bring them through the plasterboard and then have to skim around them....and I don't blame them either.

John
 05 January 2009 06:01 PM
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drzero

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You shouldn't have to derate the cable. Reg 523.7

I have installed many in insulated ceilings - always ok - always pass LABC inspection.
 05 January 2009 06:04 PM
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JZN

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Another point is that to pass the final LABC inspection, 30% of the lghting points will need to be of a dedicated low energy type.

12V or mains halogen won't help us to meet this given that the only other lighting will be in a shower room off the kitchen and this has the same style of ceiling.

John
 05 January 2009 06:07 PM
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peteTLM

Posts: 3150
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jzn, i have never and would never trust a builder to place anything for me. My (and most electricians accuracy) is spot on, builders= to the nearest foot will do.....
Just use a sharp (re:bahco) jabsaw to do the cut out once the insulation is in on a seperate (charge accordingly) visit.

watch out for the celotex dust--cutting this with saws has been banned on some sites ive been on.

P

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 05 January 2009 06:07 PM
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drzero

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When you install your cables and decide on your positions and after the customer has changed their minds several hundred times! Then mark the joists, both sides, about 75mm from centre of where your light is going so you get a 150mm gap. Make a plan of you layout and Bobs you mothers brother! Drill the correct size hole after plastering and according to your plan and you'll be laughing. Just remember - everyone makes mistakes - now and again.
 05 January 2009 06:19 PM
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drzero

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JZN

You could comply with Part L by changing some of the existing fittings, like bedroom, hall or landing pendants to dedicated low energy. A bathroom or utility room light can be changed to a 2D fitting. There are ways round things. Shoot me down if I'm wrong but I think its only 25% of fittings to be energy savers.
 05 January 2009 06:25 PM
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JZN

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Yes I think you are right on the 25%. I'll suggest the changes to the existing lighting in the rest of the house to the customer. I'll look into CFL downlights though as well.
 05 January 2009 06:37 PM
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perspicacious

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"Customer is having a single storey extension with a pitched roof."

I would suggest that whoever drew the plans for BReg approval ought to be the one from whom the client seeks advice as to whether destruction of the specified design is OK and if so, how it should be carried out to pass final BReg inspection.

It is so much easier if someone else gives the client the bad news

Regards

BOD
 05 January 2009 07:20 PM
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MrAmps

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Always a tricky one this. We do alot of barn conversions and come across this all the time. Are the beams going to be exposed? if so this poses even more of a problem. the only way we could overcome the problem last time was to build out plasterboard boxes in the skeiling flush with the beams where the lights were going. dont forget you usually require a 25mm clearance behind most recessed light fittings.

If the skeiling is totally flat then there should be enough room (depending on spec) by cutting out insulation as mentioned before.

Our BC have never questioned this, but I would check with yours

Dont forget you can use outside lights in your 25% part L allowance.

Regards
 05 January 2009 07:30 PM
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OMS

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Our BC have never questioned this, but I would check with yours


Probably because they have a SAP calc that shows a nice continuous and unbroken insulation layer in the roof deck - as opposed to the swiss cheese left after construction

OMS

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 05 January 2009 08:46 PM
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gpaul2

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too many pessimistic warnings about what might happen and not enough advice/ solutions to overcome this scenario
its ok to pont out problems that may occur but what do you do when you get to the job and roof is already on and joist are 6" deep and stuffed with celotex
tell them to remove the tiles so you can fit hoods/hats on them then you are are left with only 1" of insulation above it

Edited: 05 January 2009 at 08:54 PM by gpaul2
 06 January 2009 09:40 AM
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perspicacious

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"not enough advice/ solutions to overcome this scenario"

From my post above:

I would suggest that whoever drew the plans for BReg approval ought to be the one from whom the client seeks advice as to whether destruction of the specified design is OK and if so, how it should be carried out to pass final BReg inspection.

Straightforward enough to solve.

Regards

BOD
 06 January 2009 10:07 AM
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WalkersWiring

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Sorry for more pessimism -

I did as Bod suggests recently - cutting a long story short, ceiling mounted fittings were installed. Client not happy, but at least they had no gripes with me... Looked bl**dy awful.

Regards - Jerry.

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 06 January 2009 10:28 AM
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aligarjon

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i had a similar one a while back,with the customers consent they fitted a flat piece of ceiling about 18" wide in the apex, just wide enough for some tilt downlights.

Whats the point in fitting energy efficient lights then cutting a bloody great hole through the insulation and wasting all the energy you are so say saving with a bit of interest to boot. Gary

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