External insulation Vs cavity?

Sigma Force

Hope this is in the right section.

A lot of houses are getting external insulation at the mo and some the injectable type. Have seen three different ways so far on various house, the latest was what looked like foamy blocks attached to the outside of the wall then plastered over, the finish looked really nice.

Do they all do the same job? Or is one better than the other?

The old section of the house has no insulation in the walls, stupidly didn't put any insulation in between the old wall inside and new plaster board. Don't want to go through the mess and expense of ripping down all the walls do insulated them now. So with that type of wall what would be better, insulating the outside or injecting insulation into the walls?

The old part of the house on the outside has old kind of pebbly dash on the gable ends which looks awful and it a b***h to paint so thinking external insulation would help with the look but practically not sure if that's the best?

Any opinions?

BryanF

stigma,
this should be in the construction section, maybe one of Mods will be kind enough to move it. but here goes anyway:
we need more info here, but from what you've said there is no cavity, so forget 'injecting'. I'm going to presume your 'old wall' is a rubble stone wall held together with lime, so I would suggest you consider an appropriate solution that complements the wall structure. imho the best option is a hemplime insulation mix with a lime render finish, with the second best being a rigid suitable mineral wool product for external use with a breathable render finish.
whatever you do, do not apply a standard EPS/ PIR solution.
you should note its best to look at the overall 'holistic' approach when considering wall insulation and employ a professional that understands conservation and retro-fitting best practice.