downlight advice

[GT1]

Hi guys.

Im looking for any hints or tips to help me with a job coming up some time soon.
Its nothing particularly challenging technicaly, its kitchen downlighters..!

But ive been fairly fortunate so far and not had any griefy downlight jobs other than bathroom replacements. This job has grief written all over it though.!
Im happy with the wiring side of things its just the physical process of working through the holes in the ceiling and crossing joists.

Im concerned that my first hole will be under a joist for a start..!
and then the prospect of getting cable through joists inside the void..?

Anyone suggest any tricky tools to help out.
Sorry this makes me sound a bit green, but frankly I could do with help on this one. Been avoiding it up to yet, but cant turn this one down.
Cheers.

 

[rocker]

Ha yea I love those sorts. I like to give it to them blunt: 'Yea, well, I CAN do it and i will do it, but it'll all be in minitrunking. Have you seen minitrunking or shall I get some off the van, so you can have a look at what it looks like? Now, do you want me to put it 'real' vertical, or in line with your wonky walls?..... No, it will look out-of-place whichever way I do it'.....

Normally offering their services as floorboard lifters after that.

 

[martysparky]

Reminds me when my Mrs had her council house rewired and they wanted to trunk everything.

I simply said " look guys I am not going fishing so i suggest you get phishing

A few laughs and days later her house was the only one with no trunks and didn't look like an rampaging elephant had visited.

 

[pennywise]

The best tool I've found for doing downlights with no access to the ceiling from above, is a 400mm flat wood bit, you cut the holes for your lights and then drill through the joist through the holes you've made, in a new build there should be a clear run with no noggins. Another tip for finding the first joists to accertain the spacings is to use your super rod magnet attactment or just a strong magnet run it over the ceiling slowly until you get a bite from
a drywall screw or clowt nail head, then work logically left and right until you find another joist.

 

[rocker]

The best tool I've found for doing downlights with no access to the ceiling from above, is a 400mm flat wood bit, you cut the holes for your lights and then drill through the joist through the holes you've made, in a new build there should be a clear run with no noggins. Another tip for finding the first joists to accertain the spacings is to use your super rod magnet attactment or just a strong magnet run it over the ceiling slowly until you get a bite from
a drywall screw or clowt nail head, then work logically left and right until you find another joist.

400mm?

 

[pennywise]

Sorry 20mm but 400mm long. I would love to see the downlight that would have covered a 400mm diameter hole

 

[Sintra]

I would have loved to see the bit. It would be like a rotating shovel.

 

[martysparky]

Maybe missing something here....pennywise

I figure you only drill joists with that method locally to the fitting and the middle ones cut out to reveal the joist.

Joists are usually about 400mm apart so if the fitting had to be 150mm from the joist that would mean two joists to pass and the 400mm bit could reach from the whole for both joists.

If the fittings were more than 1200mm apart cable would need pass 3 joists and the fittings would be 1400mm apart. Two of which are accessible to drill.

That would mean only the middle ones need cutting out

Doing it like that I would always be in fear of crashing the drill into an invisible pipe or a cable.

 

[Smugley]

Before going for it with the hole cutter, drill a 7 or 8mm hole and 'feel around' with a bent wire. You can learn a lot by feeling how far the joists are away from the hole, and whether there are other obstructions in the way such as pipes or cables. If you bend the wire about 150mm from the end and you can spin it around freely, lifting it up and down, you'e right in the centre. Bend it at about 200mm and you should be able to tap the joist on either side. Never had any success with my joist detector. Waste of money I reckon.

 

[Bright Sparks]

Downlights are a constant pain, as manufacturers instructions require 50mm air gap between them and joists. I have seen before them up tight against a joist, even in one instance the joist part drilled to accomodate the fitting. This is a big no no, halogen lamps 50w get up above 200 deg C. Expect a call from the fire brigade and a court summons. If the lighting plan don't fit the joist pattern, change it.

As a previous memeber wrote, the only real way is to lift the boards above or post box the ceiling to check the joists then repair afterwards.

Hope that helps in your decision making.

 

[Bright Sparks]

Oh sorry forgot to mention, standard 30 minute fire rated ceilings in most houses are a single layer of plaster board (Skimmed) with joists 600mm apart. There should be plenty of space to add downlighters! (90 minute ceilings by contrast are 2 layers of plaster board with 450mm spacing).

 

[martysparky]

Before going for it with the hole cutter, drill a 7 or 8mm hole and 'feel around' with a bent wire. You can learn a lot by feeling how far the joists are away from the hole, and whether there are other obstructions in the way such as pipes or cables. If you bend the wire about 150mm from the end and you can spin it around freely, lifting it up and down, you'e right in the centre. Bend it at about 200mm and you should be able to tap the joist on either side. Never had any success with my joist detector. Waste of money I reckon.

Have you tried one of these
Bosch DMF10ZOOM Metal Detector / Wall Scanner - Measuring & Detecting, Detectors, Metal & Studs etc

or

Bosch D-Tect 150 Professional Laser Wall Scanner Metal / Wood / AC / Plastic Detector : Tooled-Up.com

 

[Smugley]

Have you tried one of these
http://www.tool-net.co.uk/p-329104/bosch-dmf10zoom-metal-detector---wall-scanner.html

(Yep, the DMF10 Zoom is the one I have. Never felt confident in the readings it gives. Maybe just need to spend more time practising.)

 

[martysparky]

Me too. I do find it a use but it does make you wonder a lot.

 

[volt-dropping]

Oh sorry forgot to mention, standard 30 minute fire rated ceilings in most houses are a single layer of plaster board (Skimmed) with joists 600mm apart. There should be plenty of space to add downlighters! (90 minute ceilings by contrast are 2 layers of plaster board with 450mm spacing).

Good reference above.
In rare cases if the joists are long enough they may brace them with "soldiers" mostly in the centre of the ceiling . If these braces are the same depth as the joists you will have no wiring gap so the run in length with the joists is effectively halved.

Rare but worth keeping in mind.

 

[jeremy]

Is it still acceptable, rather than drilling a hole through a joist, to notch it and then protect the cable with a safe plate (metal plate with spikes to stick into joist, top or bottom0 . TLC direct sell them. An alternative also to a flexicam thingy is holesaw a hole big enough for your phone to fit into, and then, uh, take a photo. I was amazed at the simplicity of it! Refilling the holes is easy too. 2"x1" batten about 2" longer than the width of the hole, ( 2" is about 50mm for you youngsters!) Drywall screw the wood across the hole and then screw the plasterboard plug that came out of your holesaw to the wood. Fill with tetrion and Bob's the relative of your choice.Hope I'm not repeating too much of what has already been posted.