Alot depends on the extent of the damp and whether all rooms are affected. We were qouted £1300 for a full damp course with 30 year guarantee for a 3 bed semi that was for every room when we looked at a house about 2 years ago.
When we sold our house damp came up on our survey and we had to have 2 rooms injected and that cost £200.
All I would say is do your research on companies that specialise in this sort of thing as I have seen the effects of cowboys and it is very expensive and messy

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