Valiant
As regards the cost, half-hour rated fire doorsets can be purchased for about €250-€350 per unit (bear in mind its not just the door that needs replacing in most cases, but the frames as well). Your existing timber stud or blockwork walls might well be half hour fire proof as they are.
It is impossible to accurately price a job without seeing it, and your agent should have a good grasp on the works required and be able to spec it up for you.
You are also basically asking how often do people not comply with the law, which is probably not going to be answered here. My advice is obviously to comply with the law, as it is there for a reason.
What are the real consequences if you dont comply? Well, if you have a house fire, someone sleeping on the second floor may not be able to safety escape from the house. On top of that an insurance inspection afterwards might well spot that you did not comply with the building regulations, site clause xxy of your insurance policy, and refuse to pay out on your claim.
I have not personally heard of the insuance problem happening in practice, but the possibility is cetainly there.
The most important fact however, its that its a fair jump from a second floor window.
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