Engineered Wood floor over original suspended floor…. Can I insulate between the old and new floor?

[KHit]

We have original suspended wood flooring in the whole of downstairs in our house (Apart from the bathroom) , we have lived here for over 13 years and used to love our original boards …. However, the older we get the colder we get , and the cold , draughty floors aren’t as appealing as they used to be . We had them insulated from underneath but I can’t say it’s made much difference.

We are looking to lay new engineered wood flooring over it, can we add some layer of insulation between the old floorboards and new engineered flooring? Will it make any difference? Has anybody done this/have experience of ?

I wonder if we are delusional thinking this will make difference to how cold the floor will feel?

many thanks in advance for any responses and advice given

Yes I've done this. It does make a massive difference. It also covered the gap between the floorboards and the bottom of the skirting, which I think was the biggest draft.

And less spiders.

Thank you so much ! That’s very reassuring!
I take it you haven’t removed the skirting’s before you laid new floor? We would ideally like to avoid removing them.
what did you use between the old and new floor ? What insulation?

No I wasn't up for a replastering job, so left the skirting and used trim. The insulation is like a foam covered in foil.

Thank you!

We have stripped wooden floorboards. I've been a bit wary of covering them up as I think that although the drafts are a pain, leaving them uncovered does help prevent damp/condensation as they allow the air to circulate and the house to breathe. Interested to see the responses you get though OP!

The devil is in the detail OP...

1. You have currently insulated the void underneath your original floorboards

How?
a) Breathable membrane tacked into hammocks between the joists and filled with mineral or glass wool, then covered with a DPM sheet before the floorboards were re-laid?

or

b) PIR insulation boards with DPM silver sides that have been taped with that special tape (name escapes me, sorry) to prevent cold bridges?

1. If you have a or b, what you have had done means the combination of remaining void airflow and the DPM sheet’s position below the floorboards redirects the humidity to dissipate downwards through the breathable membrane and out of the air bricks

1. Therefore, I would have thought putting further insulation (given wood flooring underlay tends to come with a DPM barrier also) between the old floorboards and new engineered wood will lead to trapped humidity between the old DPM sheet and the new underlay - causing condensation that would surely lead to rotting of what is ‘trapped’ between both sheets of DPM - the original floorboards?

Can anyone else comment about whether my understanding of the physics of this setup - as outlined above - is correct please?

Thank you, that’s an interesting point you are raising.
we had mineral wool insulation under the floor boards but I am unsure if any damp proof membrane was used. Guys accessed the underfloor through couple of hatches and we haven’t actually seen the “final result”.

Usually, if there is a ventilated void below the floor (via air bricks) there is no requirement to use a vapour impermeable membrane in the floor as warm, moist air from within the building permeates through the breathable insulation and is evaporated away.

A vapour barrier or DPM can be installed but this must be to the warm side of the insulation. If it’s placed to the cold side, warm moist air will permeate through the insulation and condense out on the inside of the (cold) impermeable membrane.

Thank you for this. We do have air bricks in below the floor level . But unsure if anything apart from the wool insulation has been fitted.

with regards to ACG84 message , has anybody had experience with this ? Would thermal underlay potentially cause condensation to original floorboards, if damp proof membrane was installed with the underfloor wool insulation?

I find this topic a little confusing - but think Missherso and myself are saying the same thing in different ways.

I had the void under my ground floorboards insulated (it is about 600mm deep; but I had insulation fitted between 100 – 200mm deep – Rockwool batts, using the ‘hammock’ method I described and highly breathable Klober Permo Air membrane)

(I have attached stock photos from the internet showing what was done for me)

Missherso, I elected to have a DPM sheet installed between the insulation and floorboards (i.e. to the warm side of the insulation) because I wanted to prevent ‘downwards’ warm air loss from the building (re: ‘moist' air - I have a loft PIV and 2 humidity extractor fans in the kitchen and bathroom passively dealing with that)

OP, it doesn’t sound like anything other than mineral wool insulation has been laid at yours (although I wonder how it is being held up off the floor?) – which I guess implies no DPM

I am following this topic with interest; because my floorboards are in poor condition; and I’d rather have high a nice clean, easier-to-manage quality waterproof laminate floor (Quickstep Impressive Ultra)
I am in 2 minds about whether to use Quickstep underlay which I am aware has a vapour barrier element to it – for fear of causing the exact problem I have tried to describe above

So any further helpful insights from anyone would be useful for me

Hello, yes ACG84, your approach is correct where you have the VCL to the warm side. A semi permeable breather membrane is used to the cold side - this can help support the insulation.