Hardboard ceiling sagging

[Gordopolis]

Hi,

I wanted to cover over the fibre-glass stuffed joists on my garage with a basic ceiling, so i decided on hardboard.
I have pinned and screwed the hardboard sheets (1980mm x 780mm) onto the joists, which are about 550 mm apart, so each sheet is atatched to 3 or 4 joists.
After a few days though, it looks like the fist few sheets i put up have sagged slightly.

Is this normal with the approach i am taking and can anyone recommend a fix for this or a better way/material?

Thanks in advance

 

[big-all]

heeelllooo Gordopolis and welcome

you measure the centres for this job yours are either 600 or 2ft

i would go for 6mm exterior ply in 8x4ft sheets if you want sag free
or 12mm ply if you intend to hang things from it

you could also use 12 mm osb/strand board if you want a cheaper but not so smooth alternative

do not use chipboard or mdf