All too often we hear the view that if the owner has "done the works, then he has crystallised his claim". Whatever has been paid, is the amount you will have to pay to settle the dilapidations. So that there is virtually no point in defending yourself. It is therefore suggested that a section 18 valuation will be futile.
But we are
pleased to advise that our experience is most usually the reverse.
With some irony, judicial support for what we experience in practice is found in one of the key cases cited by those who might be defeatist.
Quoting from the CA judgement in Crewe Services & Investment Corporation – v – Silk 
"At the end of the lease the cost of repairs, or that cost only slightly discounted, may be the best evidence of the diminution of the value if the tenant fails to lead evidence that the diminution is much less".
The words in bold are as clear an instruction as one could be gifted!
The all but universally mistaken approach to applying section 18 is that "costs" and "value" are [about] the same. As a rather crass, but stark, analogy, imagine adding a £50,000 Amdega oak conservatory to a 3-bed semi-detached 1930’s council house. Do you think you add anything like that amount to value?!?
Put in context, some examples of relatively expensive costs that, on the balance of probabilities, have little or no impact on value in our experience include:-
Dented cladding on [especially older] industrial properties;
Painting of concrete floors and/or steel columns in industrial properties;
Pointing to Victorian fronted High Street shops;
"White boxing" stock areas/upper floors to High Street shops, especially when such upper floor areas are now generally surplus to the requirements of most modern retailers. In other words, they have little or no value in any event.
Patching suspended ceiling tiles to older offices, which house outmoded lighting in any event.
This is far from an exhaustive list.
The pdf involving the former Blacks shop in Canterbury included in our CASE STUDIES is a good example of what we commonly achieve in practice.
From the owner’s perspective, there are items in respect of which the cost of rectifying them will almost always have a commensurate impact upon value. Flat roof repairs in particular.