Floorboards on Floorboards

[Jamesjf1]

Hello

My 1st time on here, so be gentle with me!

Re: two ground floor rooms in a 200 year old cottage, I'd like to lay 16mm floorboards over the existing floorboards and varnish them. One room has the original joists and 28mm floorboards with bare earth below. The other has been recently renewed with 20mm floorboards on brick/timber plinths over a DPM & concrete screed.

Why not just sand the existing floorboards? Aesthetics (some of the boards aren't great), but mainly because I want to add an extra layer of timber for insulation - this is Scotland after all! Surely this would be more effective than doing what I've already done elsewhere i.e. filling floorboard gaps with papier mache/flexible sealant.

I would like to enhance this by adding a thin layer of insulation/underlay sandwiched between the 2 layers of floorboards. But what (if anything?)
I assume it would need to be breathable (e.g. fibreboard?), but I am confused about the difference between laying floorboards above floorboards rather than, say, "natural wood laminate" for which all manner of underlays are recommended.

Any advice appreciated. Thanks.

 

[mointainwalker]

What you intend doing will give you no wothwhile additional insulation but will cost you a decent amount of money/time/disruption

From memory, softwood has only about 25% of the insulation value of polystyrene or fibre-wool, so 25% of 16 mm will not be noticeable.

In room 1 how deep are the joists and how much below the joists is the earth ?

In room 2 how deep are the timber/brick plinths ? They sit directly on the screed ?

 

[Jamesjf1]

What you intend doing will give you no wothwhile additional insulation but will cost you a decent amount of money/time/disruption
From memory, softwood has only about 25% of the insulation value of polystyrene or fibre-wool, so 25% of 16 mm will not be noticeable.
In room 1 how deep are the joists and how much below the joists is the earth ?
In room 2 how deep are the timber/brick plinths ? They sit directly on the screed ?

Thanks for replying Mountainwalker
I saw another layer of floorboards as a "rustic" alternative to installing a covering layer of 1). Carpet - Will soon get filthy; 2). Laminate - don't like the stuff; 3). "Real wood" flooring/laminate - not sure about it, and expensive too.
Usual stats given are 15% heat loss through the floor of house, plus there's the up-draught of cold air from below through floorboard gaps etc. So I thought another layer of floorboards would help eradicate that, plus cover up the ones below where they have been damaged through plumbing & electrical work access. (A Building Officer friend says wood is a good insulator - just to add to my confusion!)
There are other queries on this website about overlaying floorboards parallel or perpendicular to existing ones, and "WoodYouLike" recommends putting nothing between them unless the existing ones are uneven. To answer your questions:
In Room 1, the joists are 6.5" and are min. of 3" above the earth.
In Room 2, the brick plinths are 6" high, built directly on to of the screed.
I'm not keen on lifting the existing boards to install insulation below, especially in Room 2 where they are in good condition.
Thanks.

 

[mointainwalker]

Ok - I thought insulation was your main concern as you wrote :

but mainly because I want to add an extra layer of timber for insulation -

You are right about the draught blowing up through the floor but extra boards won't cure that : an: "uninterrupted " single covering such as either a carpet or hardboard/chipboard is much better

I'm not keen on lifting the existing boards to install insulation below, especially in Room 2 where they are in good condition.

Far and away the most effective thing you could do.

 

[JJay]

OK, considering you asked this question in March, this may not be of any use to you but here's my penno'worth.
I had similar issue on ground-floor of my old house - boards poor condition and really gappy/draughty

In hall, I laid wide boards down on top of existing suspended floorboards - parallel but in a way which covered the existing gaps. Didn't use T&G.
Nail fixed through (both boards) into the joists and the floor looked entirely authentic. No draghts!!! Only prob was that due to machining of some boards, there were some gaps which showed boards beneath - However, as floor was finished with dark stain, I just put a little stain between the gaps and without being on hands/knees and a magnifying glass, no-one would ever know.
In dining room/living room, did same thing but laid T&G - again no draughts and very warm house.

 

[JJay]

an: "uninterrupted " single covering such as either a carpet or hardboard/chipboard is much better

And just one other thing James, T&G would also serve as "uninterrupted" although personally, I don't feel it's absolutely necessary.