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?
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
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.
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
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.
Fair comment. If you have been braving the heritage sites for
information 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). 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.
 IME, on insulation, they tell you to be very careful, give you all
the options but stop short of actually making any real recommendations.
 Cross batten and add another layer if you don't have that much joist
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
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.
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.
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)
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!)
Windmill, snipped-for-privacy@Nonetel.com Use t m i l l
J.R.R. Tolkien:- @ O n e t e l . c o m
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 Â£500k).
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
J.R.R. Tolkien:- @ O n e t e l . c o m
On Sunday, December 9, 2012 2:42:18 PM UTC, Geoff Pearson wrote:
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".
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