How to add extra ceiling insulation?

[monkeybaby]

Hi, looking for some advise.

Currently, my kids bedroom are quite hot during summer and I was thinking of adding additional insulation batts in the ceiling for their bedroom.

Just wondering if

1) it is safe to add additional batts on top of existing ones. Currently we already have R4 batts installed from the builder.

2) How much extras can we add?

3) Is there a specific brand/type I should use?

Looking to DIY assuming it's safe to do so.  I've been in the roof space in the past due to roof leaks so I'm comfortable doing so.

Thanks in advance.

[monkeybaby]

Thanks Mitchell.  All makes sense.  I only supplied the photo in case there is an issue with space between the ceiling and the roof/roof tiles because I've read somewhere that there should also be sufficient spacing between the two to allow ventilation and to avoid moisture build up which could cause mould to grow.

If this isn't a known issue, I will proceed as discussed and appreciate all the assistance given.

[MitchellMc]

That's more of an issue in flat roofs than pitched @monkeybaby. Looks like you have plenty of space there.

Mitchell