Re-laying floorboards over Ply Sub floor?

[lovelyjob]

I am just about to start fitting new joists to a suspended ground floor in a very, very drafty Victorian terrace. I've spent some time clearing out the under floor of debris earth and crap and am improving the front to back ventilation of the ground floor...so it's going to get even draftier! 2 rooms about 3.6m sq each. I have enough original square edge floorboards for 1 full room, with probably new ones to match in the other room. I like the original floorboards, It's such good timber I can't bring myself to get rid. Especially having found out that there worth a few bob. (I've seen prices for 6.5" wide original floor boards ranging from £36 to £54m2!)

I will be celotex insulating between joists (75mm in 100mm deep joists. Central sleeper wall, so they only span 1.8m max) and then was going to screw fix 18mm ply to the joists, finishing with the original boards screwed down to the ply. I am also thinking of a paint and then protective laquer finish to the floor boards through the 2 rooms.

I can't seem to find much on fitting floorboards OVER ply, it always seems to be the other way round. Is what I'm proposing a flawed idea, or am I missing something.

Also, re the ply...what is the spec for this situation. I see WBP mentioned all the time, but also read this spec changed years ago and is no longer an applicable term. The new codes seem to relate to the timber make up..EN-636...and the glue spec...EN-314. Confused...I am!
What is the spec for the plywood I should use in this situation. Under floor will be well vented, but the floor will be suspended 8" above damp earth.

So can any of you guys and gals give me your thoughts on the above concept please. If I'm on the right track, can you also advise on the laquer finish to the boards. I remember many years ago using a 2 pack cat laquer on some stained OSB flooring I spec'd as a designer...but I've long since forgotten the details. All I remember is that the floor we layed (8' x 2' T&G OSB to concrete 1st floor btw) still looked superb after 5 years office use.

Look forward to your replies as usual.

 

[noseall]

Whenever we build an extension we either board out in ply (bathrooms etc) or pine t&g floor boards.

If the customer then wants say a decor oak floor board fitting we then hire a porta-nailer and fix them down with this. The nailer fires a hidden nail through the tongue whereby you hit the striker with a rubber hammer. Easy. The most recent one we fitted, the customer wanted all the planks fitting at 45 degrees to the room!

Because of pipe-work beneath we used a set length nail so that there would be zero penetration through the pine floor boards.

Look here.

 

[lovelyjob]

Thanks for reply Noseall. Unfortunately not planning to use T&G floorboards at the moment, as I have 1 room of square edge boards available...and T&G would be difficult to get up if nailed or screwed down on the plywood base. I'm still considering using T&G ply for the sub floor tho..the most readily available seems to be the WISA Spruce floor, which comes in T&G 8' x 2'. This is handy for me, as a small bloke working on my own. The 8' x 4' squares edge sheets are cheaper, but I would have to get them cut in half for ease of handling. There's no way I could manouvere full sheets around heating pipes, hearth etc. So not decided on the ply yet.

As I mentioned, I'm slightly confused by the plywood ratings knocking around on the web. WBP is mentioned continually, but as far as I've read, qualities vary considerably and WBP is not actually a relevant spec anymore. So a bit more research is required there.

Any more thoughts most welcome.