Expert: Bruce E. Johnson - 11/8/2008

Question
My existing entry door is a  double french door with side lites. It's a prehung unit and 8ft wide.  The house sits on a concrete slab and there is a tiled concrete step just below the threshold.  The door sits facing my neighbors fence (5 feet).  My house is two stories.  Most of my downstairs is one great room. I haven't been able to find anything on how to frame for a "bump in". I would like to move the door in about 2 feet and remove the side lites and mount them on the side of the bump in (as windows) so that it looks like this inside

         side lite ---->\________/ <---- side lite
                          french
                           doors
The I guess framing is doable as I don't have to worry about a load bearing wall but my main concern is water leakage around the threshold ( a problem I'm experiencing now).  Any help would be appreciated.

Answer
Hi Bobbye, leaks under doors is normally caused by the following situations or a combination:
The first being that there is not enough positive drainage away from the door.  To alleviate this you would need to slope the inset slab away from the new door location somehow.  This may involve chipping enough of the slab away that will allow you to float (using a cement topping mix) the entry away from the building.  
An alternative method to this is to build up the slab where your new walls and doors are going to sit if you can deal with a 1/2" of extra threshold height inside and then slope a topping out with positive drainage. This is done by determining where the inside of your walls are going to be located and marking them on the floor.  Put a 1/2" strip of plywood or other material around this line to use as a dam or formwork to float your topping mix to.  Use this as the high point and the outside of the existing slab as the low point and use a straight edge for a screed to shape the topping mix so that your slab slopes to the outside.
Secondly you need to seal under the new framed walls and the threshold when they are erected.  This is done with some good heavy beads of caulking.  I like to use a urethane caulk for this.  I put two continuous beads down before standing up the walls and before setting your door threshold.  One bead close to the outside of the wall and one bead close to the inside of the wall.  Try to be as continuous as possible because even a small gap will allow water to get through.   Then before putting the finishing touches (trim, siding, etc.) on the exterior walls put another bead of caulking along the joint between the wall and the floor on the outside for one more layer of protection.
Then when it is all said and done and the exterior trim is installed and the threshold is in place put another bead of caulking all around the exterior at the base of the walls and in front of the threshold.  Being sure to caulk the wall trim etc. around your windows to prevent wind blown rain from getting inside.
I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com