All depends if you know what sort of carpet and underlay the client is having. For all you know they could be having a thick pile carpet and superduper underlay, or could be having a cheapo rubber backed polypropylene carpet mm's thin, with newspaper underneath.
I usually allow 1/2" (12mm) then offer to come back and trim the door further if necessary.
I think the OP means how much longer than the door do you make the lining?. You wouldn't hang a door and leave no gap under the door for carpets , would you?. (I'm assuming that anyone installing a door lining, knows it goes all the way down, unless someone has planned ahead and is having engineered oak flooring)
PS, I'd like to see the builder that can build a wall that doesn't start at finished floor level, but 1/2" above it.
you don't make the lining longer than the door, you make the door shorter than the lining.
It helps to put a hardwood threshold under the door, to reduce any change of height. I'd say 12.7mm is a good starting point if the room is going to be carpeted. Hanging the door on lift-off hinges makes it far easier and quicker to do any subsequent adjustment, which far outweighs any additional hinge cost.
you don't make the lining longer than the door, you make the door shorter than the lining.
It helps to put a hardwood threshold under the door, to reduce any change of height. I'd say 12.7mm is a good starting point if the room is going to be carpeted. Hanging the door on lift-off hinges makes it far easier and quicker to do any subsequent adjustment, which far outweighs any additional hinge cost.
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