On 6 Oct, 18:08, Jim K wrote:
On 6 Oct, 00:10, "js.b1" wrote:

You can insulate on the outside, but unless that is rendered it can
significantly change the character and may be prohibited if a Gr-II
listed building etc. If possible, however, you can the thermal mass of
the inside as long as you can stuff enough heat into it in the first
place. You would use polystyrene stuck to the wall with plastic pegs,
with an expanding mesh, and a render coat over the top - or something
along those lines.

do you have a link to anywhere that has been done and works?

IMHO talking of "thermal mass" in these situations is somewhat of a
red herring as these thick walls are not isolated/insulated from the
earth they are built on....

Jim K

I have done it to my house. (DIY project.)