Help please with flat roof Marine or WPB and what thickness

[misterhyde]

Firstly an introduction. I have recently purchased a Victorian terrace, where at some time in it's life, the outhouse was turned into a tiny kitchen. I'm interested in DIY, however won't attempt to do large jobs myself, I just like to know and understand what and why my contractors decide to use certain products
I've got my head around exactly how the floor needs to be prepared; WPB will be glued and screwed appropriately, and joists secured and leveled if necessary, my question is regarding the roof.
Can I use WPB instead of Marine ply?
Do I once again need to use 18mm thickness, as I will with the floor, or can I go down a scale, maybe to a 9mm or even 6mm?
Maybe they can use OSB instead, and if so, at what thickness?
This is a great website and forum, I look forward to receiving advice from fellow members.

 

[cotswoldbuilders]

We use 18mm osb3 8x2 t&g boards.

If your doing a warm roof construction, consider insulated ply boards.

 

[misterhyde]

Thank you for the swift reply. I will certainly look into a warm roof construction, however I am on a ridiculously small budget. As mentioned, the kitchen is tiny, therefore the difference in price may not be massive. I've no idea about insulated ply boards so excuse me if I'm writing rubbish. I'm just assuming that your suggestion will be more expensive.

 

[ners]

Another vote for 18mm osb 8x2

 

[misterhyde]

Thank you.and finally, OSB grade 3?

 

[cotswoldbuilders]

osb3 is roofing grade.