I am going to lower the ceiling in the boiler room located in the outhouse. The boiler room is 4m x 4.5m.
What dimensions should I use for the framing timber? I was thinking 45x120...?
What ceiling panels should I use? I was thinking of ceiling gypsum 12.5x600x1200 mm...?
The only thing that will be on top of this ceiling is insulation (fiberglass).
What do you think? Should I use thicker framing timber and ceiling panels?
It should be added that I only use electric heating, so gypsum is not necessary for fire protection.
What dimensions should I use for the framing timber? I was thinking 45x120...?
What ceiling panels should I use? I was thinking of ceiling gypsum 12.5x600x1200 mm...?
The only thing that will be on top of this ceiling is insulation (fiberglass).
What do you think? Should I use thicker framing timber and ceiling panels?
It should be added that I only use electric heating, so gypsum is not necessary for fire protection.
Oh my god. cc60 is more than enough. That way you avoid cutting the insulation too 
Thicker framing lumber? What is on top? Unless you're also building an upper floor on the outhouse, 2x4" might be quite overkill. I don't see any reason for thicker roof panels either. A boiler room... it's almost like masonite and a bit of white paint could be enough (but I wasn't quite serious). 13mm gypsum will probably be good if you’re planning to have a lamp there, otherwise, even thinner gypsum would work, but it's not cheaper as one might assume.
Thicker framing lumber? What is on top? Unless you're also building an upper floor on the outhouse, 2x4" might be quite overkill. I don't see any reason for thicker roof panels either. A boiler room... it's almost like masonite and a bit of white paint could be enough (but I wasn't quite serious). 13mm gypsum will probably be good if you’re planning to have a lamp there, otherwise, even thinner gypsum would work, but it's not cheaper as one might assume.
If you look at the Gyproc and Norgips websites, there are quite detailed instructions about dimensions for supporting plasterboard ceilings. The two companies come to slightly different dimensioning conclusions, so it is probably not critical.
But the summary is that one should have battens (sparse panel) at cc40 or similar under the main beams. Then there are dimensioning tables for the battens regarding different cc distances for the beams above.
They also recommend that if you have one layer of plasterboard, it should be installed across the beams/battens, which makes cc60 seem a bit sparse, as this means the screws on the edge of the boards are also at cc60.
But the summary is that one should have battens (sparse panel) at cc40 or similar under the main beams. Then there are dimensioning tables for the battens regarding different cc distances for the beams above.
They also recommend that if you have one layer of plasterboard, it should be installed across the beams/battens, which makes cc60 seem a bit sparse, as this means the screws on the edge of the boards are also at cc60.