Wider Decking Boards

[glatts]

Hi fellow renovator's
First time poster here.
I am planning a decking area under my new verandah approx 70m2 and have spent hours trauling this forum seeking advice, ideas and answers. I have most of the info I need but have a few remaining questions I would love some answers too if you have the time.
My wife has fallen in love with 140mm wide Northern Box boards and I have to admit they do look great.
My questions are regarding mainly cupping prevention.
The only 140mm boards I can find (i'm in SA) are 25mm thick and I have read a few people recommend 32mm for wider boards, is it possible to get 32mm Northern Box or is it suitable as it is a very hard timber to go with the 25mm? also it has been suggested that I use 3 screws (I plan on using the spax flat countersunk screws) to prevent cupping is this really neccesary or will 2 be sufficient and does staggering the screws make a long term difference?

Thanks in advance for any replies and a big thanks to the info and effort people go too with there posts!!

Cheers
Glatts

[stevoh741]

1. A screw in the middle will make no difference to cupping and is a waste of a screw and is eye pollution
2. Staggering the screw is to help prevent creating a fault line on the joist
3. Good choice in screw using the spax.

[glatts]

Hi Stevoh741, thx for your response, I thought as much about the 3rd screw but the guy at the timber yard suggested it so thought I better ask for another opinion. Just wondering your thought re the 140x25mm board vs the 32mm do your reckon they would be ok and/or do you know if northern box comes in 32mm?

Cheers
Glatts :)

[stevoh741]

Hi Stevoh741, thx for your response, I thought as much about the 3rd screw but the guy at the timber yard suggested it so thought I better ask for another opinion. Just wondering your thought re the 140x25mm board vs the 32mm do your reckon they would be ok and/or do you know if northern box comes in 32mm?

Cheers
Glatts :)

I only use 140x32 (spotty/ironbark) and even then you can get a small amount of cupping. For it to be dimensionally stable it would need to be 40mm or so which isn't financially practical. Haven't been game to use 140x25 or 19 for fear of callback wanting replacement when it cups. have seen it down looking ok and if it is all under cover would prob be alright. I definately wouldnt use it if it was fully exposed. If you have time on your hands throw a couple of lengths in the weather (unfixed) and see how they hold up. I'm sure a few weeks of rain and sun (and hose?) will give you an indication.