Can someone point me at a reputable website that shows the amount (%) of
heat loss through a solid double brick wall? I can find lots of sites about
cavity walls but my house was built in 1923 and has solid walls.
I'm asking because we're about to do some work, part of which will be
insulating the roof (it's flat so no crawl space so insulation will be a
pain!). At the same time I'm trying to find out whether insulating the
walls will be worth the large amount of effort involved as it seems to
involve removing existing plaster (optional) and replacing with combined
insulation/plasterboard and then skimming.
a 215mm solid brick they give a thermal conductivity of 0.75, which
with a cavity they say drops to 0.54. I'm thinking of using their
ThermaLine Super to get my solid walls up to U-values of 0.35. They
give figures for leaving the plaster on, but I believe it is better to
remove to allow the bricks to breathe and thereby prevent moisture
buildup (obviously some venting of the created cavity is required, but
you don't want gales blowing through it).
as the double brick wall has a cavity
any moisture can dry out though the outside
so why cant we make the inside of the brick wall non-porous
and glue the insulation board straight onto it
without an airgap for draughts and gales?
Brick has an average k value of about 1, so a U value of about 5 for
solid 200mm brick.
Similar to a single glazed window or a solid wooden door.
To be honest, in a single brick house, the walls represent the greatest
heat loss of anything. People insulate rooves because its simple and
cheap, but there is no doubt that wall insulation has the greatest
potential benefit, but its also the greatest cost unless you dry line etc.
If you can be bothered, the difference will be remarkable. Even 3mm of
polystyrene, will knock about 30% off that heatloss.
Put in 2" of celotex, and you are knocking 90% off it. Up to the point
where its almost worth double glazing the windows..;-)
You don't HAVE to skim, if you are careful..just plasterboard up, fill
the cracks and use lining paper..
The 2" of dry lining is also a great place to re-lay cables and pipes..
If you do it a room at a time,. it doesn't seem so painful, either.
Basically get 2x2 timber, screw thriugh into the walls, lay cables and
pipes, and infill with celotex, covering over he joins with te foil
tape, so the whole wall is airtight and vapour proof, then line with
12mm or 15mm plasterboard,fill holes, lining paper and paint.
Electrical sockets can use steel boxes 2" deep screwed straight to the
Wrap pipes in insulation and run in slots in the celotex, notching
through studs as needed.
The actual difference will astound you. Walls ae no longer cold, and you
will feel warmer even if the room is cool, as there will be no cold air
draughts falling down the walls to freeze yer tootsies.
Done to a complete house, with roof a well, I would NOT be surprised to
see you halve the heating bills.
No reason at all.
There are two ways to look at damp, one is to let it get in and make
sure it can get out again.
I.e. no damp proof course and breathable walls..
The other way is to stop it getting in (DPM, vapour barriers), and what
little does, give it a path to outside, I.e. breathable bricks *outside*.
Modern insulation requires that massive internal ventilation via open
chimneys and fires cannot be used to dry out internal dampness, so the
latter way is the de facto standard under the regulations.
You almost always HAVE to use a vapour barrier inside insulation,
otherwise the far side of it will get condensation. Celeotex comes foil
Mind you, it can play merry hell with radios. Probably one of the
reasons wifi can be so unreliable.
Lay in plenty of CAT 5 when dry lining ;-)
Yes, but the dabs will have air voids between them, and this leaves the
opportunity to have a small circulating air flow between the back of the
sheet and the brick work. This allows an opportunity to remove any
moisture that has worked its way into the bricks. This flows needs to
be limited though, otherwise you compromise the insulating properties.
I'm thinking of a few small vents to the loft which is covered by a
sealed Tyvek Supro permeable membrane, which allows moisture out (like
Gortex) and thereby allows you to seal everything else up to prevent the
wind blowing through.
If you are using celotex and plasterboard combinations, that's how you
However consider using studs and sheet insulation, you can get more
depth, and its easier to arrange pipes and cables, and easier to mount
stuff onto the wall - there are wood pieces to screw things to. Its more
labour intensive, but if its DIY te better result may be worth the effort..
Also do look at windows and doors..yo MAY want to mount cills on top of
insulation to prevent losses there as well.
I assume you mean doesn't have a cavity? My house has internal and
external bricks, those on the outside have extra glazing to increase
their water proof properties, which of course is very desirable, you
want to keep the rain out. The glaze is water resistant in both
directions, so only allowing the house to breathe through the outside
bricks isn't going to work. Damp can get into the inner skin in all
sorts of ways, and although a vapour barrier will help to stop it, it
won't be 100% effective. The air gap itself also has insulating properties.
How does one engineer a breathable brick that doesn't let the rain water
in from the other direction? I haven't come across the Tyvek of the
brick world, could you point me to a link please. Were they available
and used in 1890?
No. See the diy wiki for why not. Basic explanation: Inside a warm
house there is a high temperature, and quite a lot of water vapour
(measured in g/m3, not relative humidity). Outside there is a low
temperature, and less water vapour. With the insulation but no vapour
barrier, the temperature falls steeply, but the water vapour falls
gradually. The net result is that the temperature can fall below the
dew-point and you get condensaton.
With the vapour barrier INSIDE the insulation, the vapour level falls
very steeply at the barrier, so the temperature never gets below the
The the vapour barrier OUTSIDE the insulation, things are much worse,
and you are positively guaranteed condensation, with no way for it to
Snip good discussion of why to dry line.
Although putting in new, well made, windows does allow you to
eliminate draughts which are an even bigger source of heatloss than
If you are putting in new windows, you might as well get them double-
glazed unless you need thin glazing bars for visual reasons. We were
originally disappointed with our new double glazing, but we have got
used to the glazing bars (and it certainly looks better than UPVC).
It is against the spec but I have sucessfully used TP10 (its all the
same regardless of name) 2" p-urethane ins on walls using
a) gypsum plasterboard adhesive AND external stainless steel fixings
b) followed by plasterboard and skim also fixed with adhesive and
fixings (spaced differntly to those under)
If you want to minimise space loss it is the best way forward
If you want to you can use drywall topcoat vapour check on the inside
It worked a treat for me
The purpose of the vapour barrier is to keep your steamyy interior, full
of steamy dogs, and cups of coffee, from getting PAST the insulation to
the cold part of the wall, where it will condense and form a nice
habitat for fungus. Which will rot the studowork in time.
Water ingress from outside is what the brick wall is there to stop, and
the theory is that if it gets in that way, it can get out that way.
You COULD shove a DPM in between te stids and teh brick, but hat runs
the risk that if water DOES get in by e.g. dripping down from the eaves,
it cant get OUT again via the brick..and then you might get rot at the
Wll AFAIK its quite simple. All bricks are pourous. If siake on te
outsie, they will in time get damp n te inside.
However bricks are built into walls, and water runss off walls, so teh
damp never penetrates that far. It tends to cling to teh brick a well
when its arrived via the rain, so the inside wont drip. It will just be
damp, and once teh brick is full of water, it is in fact waterprof..in
te snsen that to actialyy force water through it takes pressure. Maybe
on really DRIVING rain a bit gets through, but no big deal.
When the rain stops, the water evaporates, and the water migrates
through the brick back to the outside.
Think 'sponge' ...if you play a hose on a sheet of sponge, mostly the
water soaks in, then runs down the outsdie. Not a lot drips down the far
If there is a DPM at the bottom,its traditional to NOT bridge the inner
and outer leaves, and in fact the inner DPC is usually higher than the
outer..so any water in the cavity ends up below inner DPC level, but
abive the outer, and goes out via the brickwork.
On a single brick te wall is much thicker per leaf, and you relyy on
interior ventilation to deal with the odd heavy shower..
If dry lining it there is PROBABLY an argument to put DPM between the
lower part of it and the studs, to make sure than any water collecting
at the area above the DPC doesn't get into the studs, and instead soaks
outwards, but its going to do that anyway in all probability. A little
humidity after rain is not a huge problem: Rot happens when water
collects and cannot escape. I.e. when you tank the outside of a brick
wall becaue you think you have a penetrating damp problem at low level,
when its leaking guttering getting into the wall at high level, and
soaking BEHIND your new tanking, and now, having nowhere else to go, is
blowing the plaster inside the house at skirting level..
It is, but it has the downside of having nowhere to route wires and
pipes other than by carving it about.
Its a very simple and effective quick fix, bit I reckon proper studs and
2" of celotex, is the better way by far
so is the steamy breath in this room
seaping through the porous plaster ceiling
into the glass fibre insulation
and condensing there?
or is that that the plaster cieling is a good enough vapour barrier?
or should i go up in the attic and put plastic under the fibreglass...
or even better paint the ceiling with a waterproof paint?
and then fit a fan for controlled ventilation?
Hmm... Compare the cut edge of a brick to the outside surface and you'll
see the difference between a glazed and an unglazed surface, and the
purpose of the glaze is to stop water, in the same way it does on plates
for example. Concrete blocks are porous, hence the reason why you have
to render them, despite the fact they are built into walls, to stop the
water penetrating them.