improving floor insulation

I am thinking of improving the floor insulation of my house. Under the ground floor of my 1897 stone-built house in Edinburgh I have a space about 1.6m high under all the rooms so access for work is very good. My energy bills (gas+electricity) are about 2800 a year.
The floor is a standard Edinburgh floor: 11 inch joists with the space between filled with ash and covered in plaster, supported on riven wooden strips, themselves supported on battens along the joists. This deafening (as it is called here) is about 3-4" thick. The floor is standard 1 1/8 inch tongued and grooved boards. The space below the riven timber strips to the lower edge of the joists is about 6".
So there is space to add insulation below the deafening and access is easy.
First question: is it worth doing? With deafening in place that provides quite a thick layer - but then in more modern houses cavity walls do get insulated so maybe the deafening is not a good thermal insulator (although good for sound). Insulation is cheap enough and it is bound to reduce my costs - more importantly it might make the place warmer.
Second question: how to do it? I can put mineral wool rolls in the space and hold it in place with netting. Or should it be slabs of something? Do I need vapour barrier - I think not?
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This has been done to death on uk.d-i-y over the years and the advice given is still valid, can I suggest you have a search on google groups group:uk.d-i-y and come back with questions on anything not covered there.
With bills that high I assume draughts are a more likely source of your heat loss. Floor insulation can generally be assigned a lower priority but you usually end up fixing floor draughts at the same time. For info, a draughty 5mm gap between floor and skirting on a good sized Scottish lounge room is equivalent to having a window open 100mm. How draughty are your windows? Also, tenement or proper house, it makes a difference.
--
fred
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Actually, insulating an "Edinburgh" floor does not seem to be covered much elsewhere. English suspended floors seem to be joists and planks and nowt else so there is a lot on them. There are drawings like my house on on http://www.changeworks.org.uk/uploads/83096-EnergyHeritage_online1.pdf (page 39 et seq).
It is a mid terrace house, two storey, with virtually air-tight windows (brush strips etc), doors likewise, so the remaining obvious air entry points are though the floor (sanded bare boards with rugs). Skirtings have mouse-mouldings so they are sealed. Many of my neighbours have full basements which are semi-habitable rooms. The ground rises slightly under mine so the room shapes are there but not the height.
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Fair comment. If you have been braving the heritage sites for information[1] then you have my sympathy and are well deserving of help.
Here's my take:
The floor build isn't that different from that in the intermediate floors of Glasgow tenements but of course they do not require insulation due to thermal balance with properties above and below.
It's difficult to say why they put this in at the ground floor level except that it would provide a fire break if the basement was in use and that it would provide a basic level of insulation.
As you already have some insulation (the deadening) then adding more will put you at risk of interstitial condensation leading to rot. I think this is more of a risk when insulating loft spaces in heritage buildings and current advice there is to insulate with fibreglass or rockwool w/o a vapour barrier but to inspect the ceiling joists in the roof space at regular intervals to ensure that there is not a condensation problem. The problem is less pronounced in floors so I would still omit the vapour barrier as there is little guarantee that it can be done effectively and there is a risk of trapped (and hidden) moisture in the event of interstitial condensation or in the case of a large spill or flood from above.
The suggestion to avoid a vapour barrier unfortunately precludes the use of foil backed PIR insulation (Celotex et al) as the foil backing forms a vapour barrier.
That leaves fibreglass or rockwool applied in depth (8-10" suggested[2]). That is what I have used here ( Glasgow tenement floor) but don't expect it to be an easy fit as the concept of, "simply hold in place with netting" is a fallacy. The glass doesn't want to stay up where it is put and you get an inevitable sag when the netting becomes loaded. You can however make a temporary fix with string strung tightly between pre-placed clout nails in a diagonal, zig-zag arrangement. This then gives you time to staple in netting tightly. To get a tight fill I'd recommend an inch or so compression on the glass when the net is initially installed. Also to avoid an unintentional moisture trap I would avoid bagged fibreglass products such as spaceblanket.
By far the most important issue IMO is to avoid drafts circumventing your new insulation. This means sealing the edges of the deadening layer to make sure that not draughts can penetrate.

Well done on the windows and I assume the loft is already done? Despite my best efforts at draught proofing, I felt that bare boards were asking for it so I went for fitted carpets laid over tape sealed hardboard.
An IR thermometer is invaluable in spotting heat loss, just look cold surfaces. Also, there's nothing better for detecting draughts than crawling about on the floor with your sensitive facial skin near potential sources, they should show up easily on a windy day.
There is one final alternative and that is to rip down the deadening and replace it with close fitted and foam sealed Celotex but that would be a lot of work and very messy although it would pretty much guarantee the absence of draughts coming through gaps in the floor.
Good luck and hope that helps.
[1] IME, on insulation, they tell you to be very careful, give you all the options but stop short of actually making any real recommendations. [2] Cross batten and add another layer if you don't have that much joist depth.
--
fred
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fred
thank you so much for this comprehensive reply. Excellent advice.
I now also see that the Energy Savings Trust may do this for free (only in some areas including Edinburgh - so I will ask them to do a survey - that is free too.
Geoff
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You're welcome and I hope it goes well.
The only thing I forgot to mention was to go very carefully if there is any hint of dampness in the underfloor or if any efflorescence is present but I'm guessing you would have mentioned that if there was any.

Great, well worth a try if you can get it but they may insist on a complete package including ugly plastic self adhesive brush carriers on internal and external doors, not nice. I have seen a recent grant aided job done by British Gas subbies in a Glasgow tenement loft and it was very well done. As usual, jobsworth survey/management looking to penny pinch but the guys on the job were keen to do a good job when they met a knowledgeable householder, top lads.
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fred
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What there is in the under floor area is a non-stop blow through the house. Really well ventilated - which is good but I want to keep that out of the inhabited zone.
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On 09/12/12 17:42, fred wrote:

<pedant>
No, it really is called deafening, as he wrote. Perhaps it's an Edinburgh thing.
</pedant>
Ian
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On Sun, 9 Dec 2012 15:33:41 -0000, "Geoff Pearson"

There are no graphics on that doc, just text and boxes. Is it opening ok on yours? I'm using Foxit, which is fine with everything else.
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wrote:

Yes - even on IE9! It is a pdf which I open in Acrobat Reader and they printed.
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Grimly Curmudgeon wrote:

Fine here with SumatraPDF and Evince ...
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Just to finish the story: The Energy Savings Trust arranged for Carillion to do the work, paid for by Edinburgh Council/Scottish Government, for no cost to me in April. All complete in two hours - now I have to work out if it makes a difference.
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"Geoff Pearson" wrote in message

When we did our house re-furb we insulated the suspended ground floor by loosely stretching nylon mesh (*) across the joists, and placing cavity wall insulation batts between the joists supported by the mesh. Mesh was stapled to stop it moving, then we laid the flooring on top. Worked very well and kept a ventilated space below.
(* the sort used for fruit cages)
AWEM
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That is pretty much what I have as a result of this free work: 150mm of fibreglass suspended between the joists. I had a void of 1.5 metres below the ground floor so it was easy.
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On 22/05/2013 10:39, Andrew Mawson wrote:

Could you have supported the batts with nails? I think I'd find that easier, but I've never actually tried it
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What exactly did they do about things like wiring strung across joists?
I've asked about insulation in the past but was told that no grants were available, though the house in question sounds similar to yours: two story terraced (but split into an upper and lower flat), with a 1.5m crawl space underneath the ground floor ventilated to the outside, flat cold as all hell in winter.
I think it could be made tolerable in its uninsulated condition with 10KW of storage heating, but that would cost ~200 per month.
Luckily I grew up at a time when there was no heat in any house until a fire had been lit, remember times when water in a flower vase beside the window froze overnight, and although I've become a bit soft as the years go by am willing to add extra clothing by day and use an electric blanket by night . (Better still, though, is not to be there at all!)
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Windmill, snipped-for-privacy@Nonetel.com Use t m i l l
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I wired the house 25 years ago - I didn't have much in the way of cross-joist wiring - I mainly took it to the wall and traversed from there. I didn't have a grant - they just did it - no conditions, no personal details, no means test (the house is worth towards £500k).
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[...............]

In mine, half the size so maybe worth half that, there's a lot of cross-joist wiring (not done by me I will add) which I imagine could be a problem when adding insulation between the joists.
I'll be interested to hear of your experiences next winter.
--
Windmill, snipped-for-privacy@Nonetel.com Use t m i l l
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Where there is cross-joist stuff they seem to have torn the fibreglass and reconnected by overlapping it behind the pipe or wire - which is fine.
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On Sunday, December 9, 2012 2:42:18 PM UTC, Geoff Pearson wrote:

ut



Forgive me for repeating this story if you read it before.
The architect Hope Bagnell once described the sound insulation of Glasgow t enements (with sand/ash filling between joists) and compared it to that in (1960s) buildings. He said "in Victorian times it was boasted that you cou ld not hear a baby being born in the room above. These days you can hear i t being conceived".
Robert
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