pre-hung interior doors

i'm going to install new prehung doors. I have hardwood flooring. The doors come with a 1" gap from the bottom of jamb to bottom of door. do you normally leave that much gap or cut about a 1/2 inch off the jamb before installing?

 

If you're setting the door jambs on top of a floor that's already been laid, then you probably would want to cut some off the jamb. You'd want to check the opening where the door jambs will sit for level, and if one side is lower than the other, cut that jamb a little longer so that the head of the door will be level once the jamb is installed. Also make sure the floor is level where the door will swing. You wouldn't want to cut 3/4" off the jambs to create a 1/4" gap under the door and then find out the door drags on the floor when you open it due to the wall being out of plumb or the floor being out of level.

 

Thanks, the floors are level but I'll probably allow 1/2" to be safe. I guess thjey make them like that for carpet.

 

Sometimes the doors will be installed prior to the wood floors and the jambs are set directly on the subfloor. Floor installers have jambs saws that undercut the jambs and casing as needed so that the flooring can slip underneath. This would also reduce the gap under the door just like carpet would. I'm sure it makes life easier, though, for the floor installers if the door jambs are left out until they are done.