Ceiling material?

Morning all,
In the very near future I am going to install an insulated ceiling in a sunroom area, The roofing is corrugated iron / Alsinite, flat roof and as the roof is quite low I am opting for exposed beams, see image.
I have a pretty good idea as to how I will do the job, the question is what to use for the ceiling material, am wondering about Hardieflex or similar cut to fit between the beams and held in place with quad.
Any idea's or alternatives would be appreciated. __________________
Jon.

If you can pick up some cheap thick polystyrene foam it will insulate and can be painted with a waterbased paint. eg acrylic. I've seen this done and it looks pretty good and will self support between your joists, whereas some form of sheet may need intermediate support.

Nothing to do with your post but I note what I believe are rendered stone walls .... would like to see a pic of the front of the home as I love South Australian residential stone Architecture.

I feel foam panel inserts would be an excellent solution as well.

Thanks for the interest Steve, dont know if this is what you expected, miners cottage in the Moonta area, built around 1880.

Thanks! Lovely little palace! Not sure if you realise, but Melbourne has few stone homes and even fewer sandstone ones....... always nice ot see alternatives to the timber and brick offerings

Have fun