Foam backed board or loose insulation for ceiling?

[R D S]

We're replacing the kitchen extension ceiling, i'm happy to lose a few inches of height.

Would you fit normal board with insulation above, or foam backed board?

[tabbypurr]

Separate insulation is cheaper.

[Andrew Gabriel]

I cut slabs to fit flush against the bottom of the ceiling joists, and used foil tape to seal the joints to prevent moisture passing through the ceiling into the roof space. (Foil backed board would be another option.)

In an otherwise well insulated house, I would have put the insulation under the joists, but that marginal thermal gain was pointless on a house with 9" external brick walls.

There needs to be a ventilated (to the outside) air gap above the insulation. If there's sufficient height inside the ceiling (including for the ventilation above), you could use rockwool type insulation on the plasterboard. I'm not sure what the required thickness is now - maybe 12". This needs to be put up with the plasterboard, and I would suggest using foil backed board in a kitchen or bathroom in this case.

[Jim K..]

Some links might not go amiss...

What's above it?