Insulation suspended wood floor

[dai_t75]

Hello all,

Been lurking here for a few months, but was hoping someone wouldn't mind giving me some specific advice/point me in the right direction!

We are currently 'doing-up' a ~1895 mid terrace house. The lounge has a suspended floor which we are planning to replace with engineered oak flooring.

Currently there is no insulation under the floor boards.

A concern I have is potential damp build up under the new floor if we do insulate it. I don't know why, but the dining room is a concrete floor so at the moment. We have air bricks at the front of the house, so the only way for the air to flow anywhere at the moment is up through the un-insulated floor boards. So would insulating cause a problem in this regard in that there would be less draughts/air flow from the subfloor?

I have also had a quick search for materials and like the idea of using wool to insulate - any big concerns with this?

Leading on from this I have touched upon 'vapour permeable membranes' and 'vapour control layer' and to be honest I am a bit confused as to what I would need to install along with the wool, if anything. Any help on this would be greatly appreciated!

 

[JohnD]

you do need a throughflow of air. Insulation is laid between the joists and will not reduce air as long as you keep the airbricks clear.

If the back room has a concrete floor, this may well have been added when the original wooden floor rotted or was damaged in some other way. This is not unusual in old houses. If you were doing it yourself you could lay ducts before filling in. As you are mid-terrace there is no way to ventilate sideways unless you have abnormally helpful neighbours.

If you still have a chimney in the front room, it is sometimes possible to make a vent into it under the floorboards.

A house of that age probably has bare earth under the ground floor. If this is damp a lot of water vapour will come off it. Sometimes you can reduce it by laying thick polythene sheet and weighing it down with gravel.

Does the hall still have a wooden floor? Can you break through the interior wall under the floor to get a throughflow of air?

Mineral wool does not support moths and cannot rot, even if damp. I prefer the brown stuff treated with Ecose which does not shed irritant dust and fibres.

 

[dai_t75]

Thanks for the reply John.

I did think about retro fitting some sort of air duct into the concrete, but in the end I decided against it as it seemed like a very big job which I would not have been comfortable doing.

We are having a wood burner installed in the front room, so I could put a vent in the floorboards just in front of the hearth?

The hall has the original tiles which I think are laid straight onto the earth!

So if I were to use mineral wool I wouldn't need to worry about adding additional membranes/sheets? From what I have read the simplest way seems to be to staple some sort of netting/mesh between the joists and lay the wool in between - is this what you would do?

Thanks again.

 

[JohnD]

netting is needed to stop it falling out. You can stuff it into the gap quite tightly without cutting to a precise fit. Pay extra attention round the edges of the room where draughts will carry dirt and dust under the skirtings and leave black marks.

A vent in front of the fire will provide air to the fire without making the room draughty, posh old houses sometimes have a brass grille. There is a way of calculating the size, the fitter or someone on here will know how.

I suppose if the solid floor ever needs work, e.g. it is damp, cracked, or there is a buried pipe, you could dig it out for ducts.

 

[dai_t75]

Is 'earthwool' the stuff you mean?

I am planning to put some T&G chipboard down before the engineered oak boards. Just wondering do I need to put something between the earthwool and the chipboard? Or given that they both appear to be moisture resistant they will be fine next to each other?

Thanks.

 

[JohnD]

this stuff
http://www.knaufinsulation.com/sites/corporate.knaufinsulation.net/files/Mineral wool with ECOSE Techn.pdf

It is made by Knauf but is also sold by big chains as an own-brand, but the name Ecose will be on the packing. Note it is brown not yellow. I think I have seen it own-branded in Wickes and B&Q. I will never use the yellow fibreglass again as I find the irritant dust and fibres very troubling. One of my builder chums tells me he had a friend who had a disabling asthma attack and died in a loft (he was fairly old) so you should use a dust mask as well.

The mineral wool is porous so will "breathe" and does not need a barrier layer in floors. It does however muffle draughts if it is well stuffed into gaps, especially round the edges of the room.

BTW chipboard is an awful material and will not hold nails. Save up for ply.

Edit:
Yes, Earthwool has Ecose
http://earthwool.co.uk/

 

[dai_t75]

Thanks for all the advice so far John - really appreciate it.

The original plan was to have the engineered board running through both rooms with no threshold etc. Just been doing a bit of reading and having concrete in the back room and suspended in the front might mean this is quite tricky?

Now I'm thinking treat them as 2 separate rooms - float the floor on the concrete on underlay and nail down in the front room with a threshold between the rooms (there is a double door there). Does this sound like the most sensible option?

Other option is float it in both rooms if I can get the front sub floor level with the concrete?

Cheers.