Down lights correct procedure

[heating12numpty12]

I am looking to have 6 down lights installed in a first floor hall way ceiling. The necessitates drilling 80mm holes where the joists are to facilitate the running of cables. Two different contractors have different ideas as to how the cables should be run through the joists:
(i) would notch out a small grove in the joists and fit the cable in this, so the cable would be sitting on top of the plaster ceiling.
(ii) would drill small holes for the cable to go through the joist, some 25 mm above the height of the ceiling.

Is there a right or wrong way give the above examples?

 

[ericmark]

Drill a hole using 1/3 rule. i.e. hole should be in middle 1/3 of beam. I am sure that is building regs and there is no option?

 

[EFLImpudence]

It is not allowed to notch the underside of joists.

 

[heating12numpty12]

Thanks. Thought through the joist was the right way, but good to know the 1/3rd rule.

 

[winston1]

I assume you don't really mean 80mm holes?

 

[ban-all-sheds]

Is there a right or wrong way give the above examples?

Both wrong.

The right way is not to cut holes for downlights at all.

 

[securespark]

Yes, 80mm.

It could be bigger.

 

[Taylortwocities]

I assume you don't really mean 80mm holes?

If you think about it, I suggest he does mean 80mm holes. These holes would be made in the ceiling at the joist position so that the hole will span the width of the joist.
If so, its a cr@p way to do it. And I wish him luck fishing the cables from joist to joist.

 

[ban-all-sheds]

Two different contractors have different ideas as to how the cables should be run through the joists:
(i) would notch out a small grove in the joists and fit the cable in this, so the cable would be sitting on top of the plaster ceiling.

Joists may not be notched at the bottom.

(ii) would drill small holes for the cable to go through the joist, some 25 mm above the height of the ceiling.

Somehow I doubt your joists are only 50mm deep.

Seriously - neither of those contractors have a clue, and if you go with either of them you will be volunteering to be fleeced by rogue traders. Do not allow either of them to come in and start doing structural damage to your house.

 

[sparkwright]

I am looking to have 6 down lights installed in a first floor hall way ceiling. The necessitates drilling 80mm holes where the joists are to facilitate the running of cables. Two different contractors have different ideas as to how the cables should be run through the joists:
(i) would notch out a small grove in the joists and fit the cable in this, so the cable would be sitting on top of the plaster ceiling.
(ii) would drill small holes for the cable to go through the joist, some 25 mm above the height of the ceiling.

Is there a right or wrong way give the above examples?

I think this needs going over again, as I think you and some others have got hold of the wrong end of the stick.

(i) I think you have made a mistake here - the notch or groove gets cut into the plaster or plasterboard - not the joist. Perfectly acceptable as there are no safe zones on a ceiling. Common way of doing it when it's difficult to remove the flooring above. Bit rough perhaps, cables could get screwed into later in the future, but there you go.

(ii) Though a tidy way of doing it, very unlikely to comply with the rules on drilling joists. I take it these joists are structural? I only ask in the unlikely event they simply supports for a false ceiling.

 

[oldbutnotdead]

I'm hoping you're going to drill 80mm holes (for the downlights) where the joists AREN'T!

You mustn't notch the underside of the joists- so there's one of your contractors binned. Any holes going through the joist should be on the centreline of the joist (ie halfway between ceiling and floor), should be between 0.25 and 0.4 times the span and should be no bigger than an eighth of the joist depth- there's the other one also binned. Unlikely you'll be able to do that without ripping the ceiling down so put a channel in the plasterboard (or lath and plaster) to run your cable in and take pics and measurements of where the channels are (for your own future reference)

 

[sparkwright]

I think this needs going over again, as I think you and some others have got hold of the wrong end of the stick.

(i) I think you have made a mistake here - the notch or groove gets cut into the plaster or plasterboard - not the joist. Perfectly acceptable as there are no safe zones on a ceiling. Common way of doing it when it's difficult to remove the flooring above. Bit rough perhaps, cables could get screwed into later in the future, but there you go.