i've been toying with fitting external insulation to the original part of our house - 1930s ish semi with 9" solid brick walls.  the rear of the house is a 1990s built extension, 4" block outer skin, 6" celcon internal skin and insulation filled cavity so i'm guessing the effect of more insulation on the outside would be minimal, particularly compared to the expense of fitting it.

the main wall i'm interested in doing is the side wall of the house.  southwest facing, and only 2 small windows, it is a vast expanse of rendered brick, and is always cold inside.

my concern about fiting it is that, as the wall is built with lime mortar, putting a moisture proof covering over the whole wall would stop it "breathing" correctly and lead to more damp problems.

the other question i've got is more logistical.  where there are pipes/cables on the outside of the wall, do they need to be removed and then replaced on top of the insulation, or is it acceptable to bury them?  there is the main gas supply pipe (28mm copper) that runs along the bottom of the wall for about half the length of the house, 1.5" waste pipes coming from the upstairs shower and downstairs utility room, and power cable running inside trunking going to an outside light.  there is also the main electric supply cable that comes from the pole to the wall of the house, then runs down the wall before going through it at ground floor ceiling height, then another cable running up the same route, that feeds the house next door.

i'd guess that the main supply cable would be sensible to be on top of the insulation.  is this something that the installer is allowed to do (just wants unclipping then clipping back on after) or do i have to get the leccy board out to do it?

pipes and small cables i'm not so sure about.  i'd guess that it's not a problem having the pipes covered, apart from the access problems should they ever need repair or modification.

any input greatly recieved.


while i've been typing this, the other half has found a large wet patch on the wall i've been talking about above, behind the coats that have been on the coat rack.  the wall was actually wet, and looks like it has been for a while.  there are marks where you can see the water has run down the wall.  removing the coats and turning on the radiator that is there (very rarely have the rads on, as we have a wood burning stove) and it has dried off quite quickly.

i don't know of this is condensation or rain water coming through the wall.  "rising damp" isn't likely, as the wall is dry underneath.

have had a look outside, and there is no visible sign of damage to the render, apart from a few screw holes where there used to be trunking screwed to the wall many years ago, but these have long since been filled with frame seal.

all the windows through the house have ventilators at the top that are always open, the letterbox currently doesn't have a flap, and the floor in the room in question is a draughty wooden floor with a ventilated void beneath.  i have cleaned away accumulated stuff from in front of the vent bricks to the floor void earlier this year.  combined with the fire, which is going to encourage lots of airflow through the house, i would be surprised if this is just condensation.  

either way round, condensation or penetrating damp, would external insulation help or hinder?  i can see a positive arguement in both cases - a warmer wall should help stop condensation, and a waterproof skin will stop rain even hitting the bricks let alone soaking through them.

cheers guys

without meaning to seem overly cynical, loathed to ask advise from someone who sells it.

That wet patch is probably condensation. If the wall is cold and covered with something like coats or a wardrobe you can get a situation where there isn't enough air circulation to keep the wall warm, but is enough to transport humid air in there where it condenses.

I've no direct experience with external insulation but saw a few brick houses in Belgium that had EWI and render (or brick slips) on the outside. They looked like new houses.