Water damage to the floor framing under a door without proper flashing.

I’ve have been looking at a lot of houses lately that have no flashing or poorly done flashing around the doors and windows.  At the least it can rot out the sub-floor inside the door.  One house I looked at had so much damage from a leak at the edges of the door that the floor joists are rotting and the middle of the house is sinking.  This is why it’s so important to get the flashing details right in these areas.  Simply caulking around the trim on a door isn’t enough if there is no roof over it to stop water from hitting it.  In fact, caulking at the bottom of the door without flashing under it will ensure that any water getting in above can’t get back out, forcing it into the framing.  Water running down from above can get inside the door jambs and go straight to the framing.  Splashing water can rot out the lower portion of the jambs and find it’s way under the door sill.  It can then run back under the flooring inside the house and cause rot that goes unnoticed until it’s too late.

A properly flashed door or window will have a plastic or metal “pan” flashing under it with self adhesive flashing tape or other water proof membrane layered over this.  At the top will be a drip cap or other type of flashing to direct water out over the trim and not behind it.  All of this will work together to make sure water doesn’t get into the structure.  Any water that gets past the flashing at the top will be directed out of the building at the bottom by the pan flashing.

Door installation prices vary in large part because of how they are installed.  As always it will cost more to do the job right the first time but for about a hundred to two hundred dollars or so depending on the door size you can avoid much bigger problems in the future.