Downlighters, fire, holes and celotex

Discussion in 'Electricians' Talk' started by acm718, Oct 28, 2006.

  1. acm718

    acm718 New Member

    Good evening! Is there a definite diameter for clearance holes cut in rigid insulation when fitting downlighters to correct building regs standard? We will have 9.5mm of plasterboard and 100mm of insulation on a sloping ceiling (with additional 50mm of airgap between the insulation and roofing felt). I'm fitting the insulation today and tomorrow (I get all the nice jobs, my eyes are stinging with the kingspan dust!) so need to cut holes to poke the wires through where the lights will be. Electrician said at first fix that the holes need to obviously go right through the insulation but didn't say what size - does the hole size depend on wattage, whether there's a fire hood (which all seem to be 150mm high, which means a hood won't fit between finished ceiling level and the roofing felt) or on the type of bulb ie 'aluminium reflector type'. A twelve inch diameter hole has been mentioned on another thread, but that seems A Bit Big? As of today, we'd (well, the management, hello dear) like to use 12977 screwfix sunken/swivel wallwasher lights, but without buying one and reading the instructions, what size insulation holes do I need, and is size dependant on whether fire hood is present? Bulbs for the wallwashers are listed as MR16 12V 50watt, but could be replaced with 35watt if it means smaller holes! Thankyou in advance, I'm off for a shower and some eyewash.
     
  2. 2 wheeled ant

    2 wheeled ant New Member

    You have to have 100mm insulation gap around hole/fitting & 75mm air gap above fitting. Dont need hoods if this is loft as not a fire compatment.
    Ant
     
  3. I had a heated argument with a LABC inspector yesterday on exactly the same senario. Sloping roof no fire containment needed but thermal loss. He also has made the builder fit a further 35mm of kingspan above the plasterboard as 150mm of insulation is needed. In a normal loft job we have made a plasterboard box around the lights with the insulation over the top but not possible here. The inspector left site saying the lights can not go in, end of story unless a further dropped ceiling is fitted to house them. The client has said just fit a pendant for now, but wire for the downlights and to come back after compleation and cut out ceiling and insulation and fit the lights they want.
     
  4. sinewave

    sinewave Screwfix Select

    ;)


    You just finished watchin X Factor too! :O
     
  5. 2 wheeled ant

    2 wheeled ant New Member

    I'm fitting the insulation today and tomorrow (I get
    all the nice jobs, my eyes are stinging with the
    kingspan dust!) so need to cut holes to poke the
    wires through where the lights will be. Electrician
    said at first fix that the holes need to obviously go
    right through the insulation but didn't say what size

    If you cut 300mm circle of insulation out drill & push cable through centre, leave if for Electrician to cut correct size hole.
    Ant
     
  6. ;)


    You just finished watchin X Factor too! :O

    I have never watched that drivel, and have no intention to either, However i never got my chicken tikka balti madras last night and am ordering one right now.
     
  7. I'm fitting the insulation today and tomorrow (I
    get
    all the nice jobs, my eyes are stinging with the
    kingspan dust!) so need to cut holes to poke the
    wires through where the lights will be.
    Electrician
    said at first fix that the holes need to obviously
    go
    right through the insulation but didn't say what
    size

    If you cut 300mm circle of insulation out drill &
    push cable through centre, leave if for Electrician
    to cut correct size hole.
    Ant


    This would not meet part L of the building regs ( according to the LABC)
     
  8. 2 wheeled ant

    2 wheeled ant New Member

  9. Thermal loss. Not me but the so-called expert inspector (who looked abot 18)
     
  10. 2 wheeled ant

    2 wheeled ant New Member

    To comply with "L" Green guidance book page 127 Table 10.6
    For the average house you only need to install 3 Energy Efficient lights to comply.
    For B you must give 100mm gap from light to insulation see IEE website.
    Ant
     
  11. As you said in another thread, these guidance books all offer different info. What the inspector wants is what he gets. You don't want to upset him as he can cause numerous other problems
     
  12. 2 wheeled ant

    2 wheeled ant New Member

    Thermal loss. Not me but the so-called expert
    inspector (who looked abot 18)
    Well you have been unlucky its not written anywhere so has no right to insist on it. Should have asked for a reg no so you could look it up.
    Ant
     
  13. 2 wheeled ant

    2 wheeled ant New Member

    What the inspector wants is
    what he gets. You don't want to upset him as he can
    cause numerous other problems

    True if its alot of houses but for the average minor works etc i would just do it & give a cert.
    There will probably be another set of books out in a few years time & change it all again anyway!! you can only allow what you believe to be right at the time.
    Ant
     
  14. 2 wheeled ant

    2 wheeled ant New Member

    This would not meet part L of the building regs (
    according to the LABC)

    So what did you do box them out? What a waste!
    Ant
     
  15. acm718

    acm718 New Member

    Many thanks for the replies...
    I will be ordering some fittings tonight, along with a couple of bayonet lampholders!
    "fit a pendant for now, but wire for the downlights and to come back after compleation and cut out ceiling and insulation and fit the lights they want"
    That'll do me - there's no way I'm losing even more roomspace to even more extra insulation. We already have 25mm between the rafters and a further 75mm underneath in the sloping areas, with 120mm between rafters in the main flat roof and then 25mm underneath - compared to what was there before - early 70's bungalow = zero insulation, not even any rockwool - there's no comparison.
    I can cut out the insulation, coil the cables inside the '100mm x 2 + diameter of light fittings' sized-holes, then plasterboard (another job for me!) straight over the top - as long as I measure and draw out a 'map' for where to cut the plasterboard after building control have been, everyone will be happy.
    I appreciate under Part L, heat loss will be compromised, but there really doesn't seem to be any other way round this other than fit a pendant lampholder.
    I could still fit some form of cut down firehood over the top of the cutout (would be 110mm from ceiling to topside of insulation, so well over the 75mm height suggested) to reduce heat loss, but then that would allow heat build-up - back to square one?
    Advice much appreciated - [to the building control officer - 'you ain't seen me, right?']
     
  16. dingbat

    dingbat New Member

    ***, you just can't fit downlighters in the structure as you have described it and comply with any of the relevant regulations.

    The sooner this particular fad dies the better.
     
  17. Rabbit Rabbit

    Rabbit Rabbit New Member

    Agree with Dingbat 100% on this subject (honest Ding!).

    I was asked to go and quote for downlighters to be put in a slopping ceiling Thursday yet to be stuffed with Celotex. The not-to-be-client told me that the LABC inspector told him that there would be no problem fitting GU10's and no need for hoods!! I declined to quote adding that I like to sleep at night mind
     
  18. oscar21

    oscar21 New Member

    Whats the problem with downlights in sloping ceilings, cut a hole out 100mm in the kingspan and fit 12 volt lamp and transformer, done loads of these in extensions no problem, dosn't need to be fire rated (fire rated ceiling-fire rated downlight). Most regulations are a load of toss. Guy just tested apartment block for acoustics Im working on, he had a machine a bit like a crankshaft with hammers on it that hit the floor, he then measures the sound in other apartments. The test cost the builder £1100 but there is an ambulance station 100 yards down the road, about 10 times a day they fly past with the sirens going.
     
  19. acm718

    acm718 New Member

    Just to add to this - we are now NOT fitting downlighters ANYWHERE in the insulated ceiling areas of our extension works...

    For Fire protection - you need a big 10 to 12" hole round the lights 'cos they get hot, as has been said above.

    For heat loss - you need insulation to a certain u value, so can't cut holes unless you can offset the losses from any holes by increasing the insulation elsewhere ie the rest of the ceiling as has been said above - £££/loss of headroom.

    For condensation/coldspots you can't have cold areas dotted about, particularly above moist bathrooms, as condensation will form and cause isolated mould spots eventually - this is what has put me off downlighters.

    We're now having wall lights and a 6 to 8" lowered ceiling in parts of the bathroom for downlighters which then don't breach the ceiling structure - much easier! Thanks again for the replies.
     

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