12mm or 18mm loft boards?

[Builder2011]

Good morning.

Are 12mm thickness chipboards adequate for a new loft floor? The 12mm boards add a weight of 7.17 kg psm.

18mm boards with tongue and groove (which do not have to join specifically on centres of the new joist) are much heavier at 12.8 kg psm.

Over a loft area of 32.2 sm, the 12mm boards would add a weight of 230kg. The 18mm boards would add a weight of 412kg.

The new joists are at 360mm centres.

Has anyone put in 12mm boards at these centres?

 

[Burnerman]

I'd go for the 18mm here. The 12 could be ok for a static load, but I reckon the bend would be significant when its walked on.
John

 

[PrenticeBoyofDerry]

Use 18mm, more riged.
12mm will flex and give more easier, if there is foot traffic.