Expert: Dan Griffin - 12/30/2009

Question
QUESTION: Dan, I live in the Houston area.  My home was built in 1973.  The back porch and master bath (at back of house) sits lower than the rest of the slab (about 6").  There was not a disclosure by the seller and it's debatable but it's possible the Master bath was added on.  In the 3 years I've lived in this home, water has come in under the master bath wall opposite the porch on two occasions (both storms).  It also recedes on it's own.  After Ike, I decided to demo the bathroom - make necessary repairs and update it.  In doing this I discovered that moisture has seeped in at the floor opposite other outside walls.  I read a question sent to Bruce in 2008 (from Sergio) about a similar problem.  Bruce recommends painting the concrete with mastic and building up the floor or pouring additional concrete over a vapor barrier.  How would I address moisture that seeps under a wall and not necessarily from below.  Several contractors looked at this wall (before I tore it out) and they seem stumped as to how it could happen because you can see what looks like a concrete slab rising above the concrete on the porch.  I need help because my insurance company isn't covering it and I really don't have the money to pay someone to isolate and fix the problem.  I appreciate your time.  Thank you.

ANSWER: Ann, without seeing it I can't help much.  What is the ground level outside this room?  Is it at least 6" lower than the room.  Is there positive drainage away from the area?  It sounds like an exterior grade problem to me.  There should be a footing around the room, not a slab capped on top of a patio.  A bit of digging around the outside sounds like the first order of inspection.  I wish I could be of more help.

---------- FOLLOW-UP ----------

QUESTION: I understand.  I was just looking for any insight you might have.  There is a drainage system built into the back yard - obviously the previous owners knew about this problem and tried to address it.  Around the exterior of this room (not including the porch), the ground level is actually a little higher than the floor of the room.  But while there is evidence of some moisture in certain places, the only place water has actually come in is from opposite the porch - and it looks like it's impossible for it to come in there.  I knew you couldn't really diagnose my problem - I guess what I'm asking is what should I look for? What should the framework and the interior of this wall look like?  I know you're flying blind here - but any insight or suggestion would be appreciated.  I have some moderate "fix it" skills - but this is outside of my experience.

Answer
Ann, it is possible to have nice dry rooms below grade.  Think about a good basement, though many of them have problems.  If the walls are well damp proofed and there is a French drain lower than the basement floor that goes to daylight or to a sump, it should keep the water below the floor level.  Most basement moisture problems are caused by bad exterior grade, flower beds too close the building, downspouts not getting water far enough away from the building, or other reasons that invite water to lay against the building walls.  The first solution is always to correct exterior drainage trouble.  Code requires exterior grade to be at least 6" below any type of siding or exterior finish and requires that the ground fall another 5" in the first 10' away from the building.  This item is often not done well.  If you have a concrete "stem" wall cast on top of the porch slab, but the finish floor is even with or lower than the porch slab, water can come right on in.  Concrete is not waterproof under any circumstance, but if there is a "cold" joint between the stem wall and the porch slab, water can literally pour through the joint.  A cold joint is anywhere that new concerete is poured against old concrete - they do not bond and there is a definite open joint that may not be visible.  If you have the wall opened up, you should be able to make it leak by pouring water on the outside.  Realize that this may take some time and that storms dump much more water than you can ever create with a garden hose.  Start the water testing down low.  If you do not get any kind of leak, move the water up gradually to test siding, inside corner, and even roof and gutter.  The leak has to come from somewhere and you should be able to isolate the cause.