In article , Geoff Pearson
writes
"fred" wrote in message ...
In article , Geoff Pearson
writes
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 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
it's a ba-na-na . . . .
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/upload...ge_online1.pdf (page
39 et seq).
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.
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.
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
it's a ba-na-na . . . .