Insulating Timber Frame Building

[Gef]

I am updating a 1970s prefabricated timberframe house. The Kit was made in Canada and is very good but the walls have only 20mm of insulation (there is space for 100mm) I have taken some plasterboards and filled the wall added a vapour barrier and re boarded the wall but I don't want to do this over the whole building Any ideas on how to get insulation in (We tried injecting Rockwool from the inside but it stuck to the existing wool and didn't fill the space.

Any advice welcome

 

[Deluks]

Hire a machine and get it blown in, you can get recycled newspaper type stuff, treated with a fire retardant which can fill any small void.