18mm ply flooring… structural softwood?

[mwebber]

Before I can instal my overlay UFH, I either need to lay 6mm ply on top of my Victorian floorboards, or replace the floorboards with plywood (or chipboard, but I’m reluctant to do that!)

I think I’m leaning towards going with 18mm structural ply throughout - it frees up the planks to go elsewhere in the house where the planks are a mess and might want to keep the good ones exposed, plus it reduces the overall buildup height of the floor (planks + 6mm ply + 20mm overlay UFH + final floor covering feels like it’s getting a bit much!)

I’ve found a good price on softwood structural ply (seems a good bit cheaper than hardwood structural ply).

Am I likely to regret going with softwood rather than hardwood?! Are there significant differences in this application?

Thoughts welcome…

 

[Deluks]

The best ply for the job will be 2400x600 tongue and groove flooring ply, which is designed for the job.
Makes no odds whether it's hard or soft so spend your money elsewhere.

 

[mwebber]

Prices for T&G are higher than square edge 18mm structural ply. There’s obviously a reason for that, but I’m trying to bring it in on a tight budget.

I can’t install noggins because there is insulation slung between joists, so I’m planning to lay 18mm structural ply across the joists (ie perpendicular), cut so the joins meet on joists. Is 18mm thick enough given that I’m proposing using structural grade rather than non-structural?

It does seem considerably stiffer than non-structural when I gave it a wobble in the timber yard!

The alternative is to leave the existing floorboards in place and just overboard with 6mm ply