Smoking in a workplace

Though they are doing work in the apartment, the apartment is not a work establishment but a residence, and I doubt that there is any legal obligation not to smoke. If they are leaving the door open, you can ask them to close it. If not, it is not different from having neighbors who smoke heavily.

You could also argue that a truck is a truck and not a workplace, but smoking at work regulations apply to that workplace. That's ignored as well. But that's smokers for you, the habit comes first and stuff anybody else.

Gardner working in your garden?

@Mimi
The rules only apply to enclosed spaces so your gardener is a red herring.
However, when the first steps were taken here to control smoking at work, bar staff who smoked protested that they were barred from smoking behind the bar whilst their customers were allowed to smoke.
My truck-driving, smoking, step-son is not allowed to smoke in the cab of his truck and the same applies to cab drivers.

@Alan
The builders are almost certainly breaking the law though it is hard to see what can be done to stop it - would the commune be interested?
In any case, what would happen if they came out of the apartment and smoked in the hallway which is not their workplace? And what if the eventual new tenants are smokers?
I sympathise with you as I hate smoking but I cannot see what you can do about it.