should, may, must - what's the difference?

[YellowLawn]

i.e. which is the strongest?

background: the awful fire and the buildin regs guidance regarding the material used.

must

May is weakest (you can if you want to). Should is in the middle (it's good to do it but you don't have to). Must is strongest.

thanks

to me they all 'read' the same, that is quite strong but I rarely need to get into that level of detail.

Should - something is preferable

May - something is optional

Must - something is imperative

Must is the strongest, definitely.

12.5 The external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health and safety. The use of combustible materials in the cladding system and extensive cavities may present such a risk in tall buildings

so this is basically saying: take it or leave it?

I agree with the posts above.

The paragraph you've posted says to me that it should not happen - in this context, must not happen, because of the risk it may (is likely to) pose.

I don't read your paragraph as take it or leave it at all and it would be someone within a very cold heart who tried to argue that what they had done was okay if this relates to Grenfell.

You would rarely find "must" in legal documents in any case. Too definite and not open to interpretation

'Should' in a legal context generally means 'must'. I.e. it denotes requirements, not best practice.