Ours are not quite as thick, but around 600mm. Drilling them to inject a DPC was straightforward enough, but obviously not as simple as a brick wall, and inevitably there will be gaps in the chemical DPC. Still, it did seem to at least reduce levels if dampness, which is about as much as you can expect.
Ventilation is the key thing in damp old houses. When you start modernising them by putting in woodburners instead of open fires you lose the essential secondary function of the flue as a form of ventilation. Coupled with draughtproof doors and windows, the moisture has nowhere to go and that’s when the problems start.
A lot of older properties have also been pointed or rendered with modern cement instead of breathable lime mortar, or painted, so that the walls no longer breathe and large quantities of water build up inside the walls.
Why do they do this? Surely it’s common knowledge that you should use the correct lime mortar and plaster (and paint)? We’re seeing it again and again… older and listed properties with cement mortar and the wrong plaster 
tbh the 700mm is a guess by the surveyor. I’m thinking he probably doesn’t really know and it will probably vary around the building.
600 or 700… suffice it to say they’re bl**dy thick! Going to need a long drill bit to get through 
Trying to drill 100mm diameter holes through the walls to install extractor and circulation fans is going to be fun!
We have a local guy who has a decent core drill and will do you a hole in any wall for £100. Boiler installers will be used to it too. I once had one instal a gas boiler in a converted chapel where the wall was about 1metre thick and he didn’t bat an eyelid.
I guess once they finished the channel tunnel they needed to keep using it somewhere😉
Little job in Hatton Garden next bank holiday weekend.
Sadly, it’s not common knowledge (i.e. rendering up as you outline), and it’s just not (say) the pre-WWI properties which are affected by this, noting many inter-war properties were simply knocked-up with very shabby brickwork and rendered for an aesthetic finish and weather protection, especially in suburban locations…and this was often carried back to earlier stock. The damp proof industry vis the use of chemicals is still relatively young and the barriers to entry to this sector are minimal IME.
Yes, the older stock requires lime mortar etc, (and nothing gypsum based) but the words ‘knowledge’ and ‘builder’ don’t always go together…and the issues can take several years to reappear.
Whenever I hear the words about barrier-ing damp/moisture my heart sinks, as unless this is executed properly, it’s often just setting up a ticking time bomb – and if you have soot contamination in a chimney breast, that can work its way back very quickly.
And who nowadays wants to live with lime-washed walls?
The below is lifted from a recent article in the Torygraph and, based on this, it seems up to 50% of housing stock may have issues with gypsum based and other modern-day products.
‘According to ONS data, 20.6 per cent of the housing was built before 1919, 15 per cent between 1919 and 1944, 19.2 per cent between 1945 and 1964, 20 per cent between 1965 and 1980, 8 per cent between 1981 and 1990 and 17.3 per cent post 1990.’
@solwisesteve – just done a late edit!
Saturday… up the top of the ladder with a cordless drill with the aforementioned 100mm core bit. Took an hour… drill a little, stop and rest arm, repeat. Then, when the cut gets to the depth of the bit, chip/drill off the top of the cut to allow another half inch of drilling.
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