solid wood flooring help

[oldhatatlaminategreenatso]

Hi -same old story as previous questions but need clarification for my own piece of mind and project. Done loads of laminate so pretty handy at flooring (for a sparky).
I want to lay a solid wood floor onto original pine floorboards. I assume that I lay it at "90 degrees" to original floor boards.
Also the floor is level so from what I have read I should "float" it on an underlay, glue the tongues/grooves (pva?) and leave a 15mm gap around outside for expansion. What type of underlay should I use (not DPC I know to avoid sweating)?. It is downstairs so is an accousic underlay (green fibre boards) really needed?. Dont really want to have to step over it if it gets too high.
Experienced replies most welcome.

 

[Symptoms]

old - always for me it's a question of levels ... can you live with a height change of say at least 20mm (+) at any intersections with other flooring; if the answer is yes, and the existing floorboards are stable, then either float or nail into it.

However, we will always lift the originals and then secret nail to the joists. IMO there are a few good reasons for doing it this way: keeping the levels; retaining the skirtings (by removing the old floorboards you create a gap for the new stuff to slip under, so not having to whip the s/boards off or having to add beading of some description); guaranteed fix into the joists and not relying on the stability of the old floorboards (or the danger of nailing into pipes/cables). Yes, I know the old stuff has to come up but I think it's worth doing.

Others here may have differing views and generally there is no wrong way to do this, providing the appropriate good practice is followed for what ever method you use.

 

[WoodYouLike]

If your new floorboards are load bearing (18mm thick at least) and long enough so they connect with at least 3 joints you could indeed ripp out the old and in with the new.
But not if you go for the 'cheap solid offers' that are around: many short lengths.

 

[oldhatatlaminategreenatso]

Thanks for replies but think I may have been misunderstood.
The existing floorboards will not be ripped up, they are staying put.
Just wanted to know if it was advisable to float the new floor on it as its pretty level or should it be secret nailed. Presumably laid at 90 degrees to original floorboards. And if so what would be the best underlay to use. Its downstairs so do I really need to worry about accoustic issues???

 

[WoodYouLike]

You, you've not been misunderstood, just given more options

How wide and long are your new floorboards?

 

[oldhatatlaminategreenatso]

Haven't purchased yet but would prefer long lengths-don't want different lengths.

 

[WoodYouLike]

Ok and if the width of the boards are 100mm or wider there is no problem installing them floating on regular 3mm foam underlayment

 

[oldhatatlaminategreenatso]

WoodYouLike- thanks for advise, so just to summarise:
Lay foam underlay (same type as per laminate)
Lay at 90 degrees to existing boards.
PVA tongue and groove.
No need to secret nail.
Is this correct?.

 

[WoodYouLike]

1 slight correction: use better quality than the normal 2mm white foam laminate underlayment.

And leave sufficient wide expansion gaps around the perimeter of the floor