Fixing a 3.5kg light to ceiling

[Dp36]

hi all
I'm looking to fix a 3.5kg light fixture/ small chandelier to a plaster board ceiling in a modern U.K. house built in 2007.
Do I need to fix to a joist or will plaster board fixings hold?
If I can locate a joist I plan to use two 100mm m6 wood screws with out any rawl plug, is this too long as how thick are modern joists?
I have 80mm m6 screws also

Cheers in advance

 

[foxhole]

Existing light fitting would be fitted next to joist.

 

[endecotp]

Do I need to fix to a joist or will plaster board fixings hold?

Carefully-chosen plasterboard fixings would work, preferably more than one.
But much better to screw into the joist.

If I can locate a joist I plan to use two 100mm m6 wood screws with out any rawl plug, is this too long as how thick are modern joists?

That's not too long for the joist. It is probably longer (and thicker) than necessary for the weight though.

 

[bernardgreen]

Do I need to fix to a joist or will plaster board fixings hold?

Plaster board fixings will probably support the weight but the plaster board might not.
3.5kg is the dead weight ( static ) you need to consider the dynamic load if activity in the room above causes the ceiling to move up and down.

Fix to a joist