With all this talk of insulation, is it workable to cavity insulate
stone walls with random cavity? I would have thought so, though expect
a lot of filing holes would be needed. But I know its advised not to
cavity insulate some wall types.
A housing estate was insulated in Scotland (new build) and was later found
to have undressed stone on the cavity side....after six months or so all the
houses got damp, and I mean seriously damp, fungus growing outof walls,
timbers rotting everywhere, the rsidents had to move out while the houses
were ripped apart and the insulation removed.
The *minimum* cavity size to be filled must be at least 50mm, with undressed
stone this is impossible to gauge, some places it might be 75mm and others
only 35mm...it just doesn't fill and water ingress is the result.
So what you are saying is that all cavity fills are likely to cause
problems but that with a wide enough span, most homes get away with it?
Whilst it explains the uselessness of modern cill board sizes, it
doesn't alleviate fears of TB resurgence. I get the impression some of
us are living in time bombs.
Is it really so?
Check your brickwork with an hose pipe. If some of the bricks are
upside down it will show. Most face bricks are designed to shed water.
I doubt it is crucial but in a frost....
(Just thought I'd frighten you while we are telling horror stories. And
now children: Good night!)
Most homes have a cavity of 50mm or more, CWI isn't garuanteed under this
thickness so no (registered) installer would do it, and certainly not
undressed stone....it's possible to get it done as a foreigner, cash only,
no garuantee etc, and then twelve months later pay about 5K to have it all
Almost all CWI installers have insurance backed 25 year garuantees issued by
Who are independant of the CWI industry, meaning that even work completed by
companies who have long since gone out of buisness is still covered.
Any jobs done during the 'cowboy' period during the late seventies will
either have been repaired or demolished before now, and it's a requirement
during house purchases to provide the garuantee, so it's unlikely many
houses are 'timebombs', given that problems will show themselves within
weeks or months of CWI installation.
I realise it would only partially fill, leaving voids, but this is
still of value insulationwise. The voids would see less air movement as
a result of the cwi, so even there the heat loss would go down.
Doing the job would not be hard, just a case of drilling many holes and
using an old fashioned double ended hoover with a box in the tubeway
to allow fibres to be put in the airstream. Certainly not as easy as
standard cwi, slow but doable. I wouldnt expect contractors to do it.
Damp is the question. First I dont understand how whats in the cavity
could in any way cause water ingress. Ingress I would have thought
would be determined by the outer faces of the wall. Second, how does
the presence of a patch of fibreglass cause water to move across from
outer to inner leaf? Polystyrene would, as it soaks up water, but
surely not fibreglass, which afaik doesnt.
Puzzled of Tunbridge Wells.
It wouldn't even be noticable, sort of putting small squares of loft
insulation down haphazzardly in the loft instead of covering the whole area.
An easier method would be to stud the wall and insulate behind the studding,
and no possibility of damp penetration.
Polystyrene? it doesn't soak up water at all, fibreglass does, but only the
stuff you would see in your loft, not the treated stuff used for CWI.
Water runs down the inside of your exterior brick/stonework during heavy
rain...if you could take down the inner leaf and look at the stonework
during a rainstorm you would see a mini waterfall! - this is normal and the
cavity stops anything getting to the inner leaf, this is why brick ties have
a twist or a bump in the centre, to allow water to drain down the cavity.
I've done a diagram and put it up on tinypic:
Whether it should or it shouldn't is irrelevant, and on some walls it will
while on other walls...you get the picture, it all depends which way the
wind blows, how many cracks are in the mortar (quite a lot in most houses,
even new ones) and a hundred other factors, none of this is a serious
problem though, until something blocks the water's natural course and it
gets where it shouldn't.
I thinkthat refers to filling the width of the cavity rather than the
height, IE putting a 35mm insulation board inside a 70mm cavity, keeping it
away from outer leaf for this very reason.
Filling the cavity after construction (the method discussed in this thread)
is covered on poage 34:
c) Other insulating materials inserted into
the cavity after the wall has been constructed
should have certification from an appropriate
body and be installed in accordance with the
appropriate installations code. The suitability of
the wall for filling is to be assessed before the
work is carried out and the person undertaking
the work should operate under an Approved
Installer Scheme that includes an assessment
No accredited or approved company will fill a house built with undressed
stone in the cavity, nor would it be garuanteed if they did.
Polystyrene is impermeable.Even foam. Thats why they make buoys out of it.
Glass fibre is like any fibre, capillary action causes it to transfer
However, I don't see how the cavity would get wet either unless the rain
is pissing down the outside and its full of soft permeable mortar - or
made of soft permeable rock, like clunch.
Perhaps the issue is that some stone hoses have no DPC and need to let
internal moisture get out...
There are differing build techniques with stone depending on the type
of stone - compare for instance the small slab stones on the
Northumberland moors with the great chunks of granite in Aberdeen.
In my own cottage - sand stone and whin - the walls are approaching 3
ft thick and consist of outer and inner skins of large stones with lime
mortar, and all the rubbish - and that is what it was called - goes
into the middle without any mortar. It's a real pain when you are
making a hole right through for pipes,etc as the small stones just keep
on falling down.
Now to insulation - the original stone floors were replaced in the 20's
with fully vented wooden floors and the walls were lath and plastered.
Unfortunately they hadn't heard of insulation then and all the
underfloor ventilation went up to the roof space behind the L & P;
result freezing cold rooms permanently. So off with the L & P -
restrap, rockwool, membrane, plasterboard; result warm house. That's
the way to go but it is possible that may not work for you.
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