I have a house that I swear was designed and built by an idiot.
It is now 22 years old and literally falling apart at the seams
The house is build on a cement slab, the slab extends out from the
foundation on two sides (side and back of house) and is level with the
foundation. This means that the sill of the house is sitting at the
same level as the "outside" slab so when it rains the water runs down
the house, hits the slab and rolls under the sill and rots out the
sill, the siding, and the trim that have all been installed down to
the slab. I hope this is understandable I have added pictures below.
Now I have removed the rotting trim, siding, etc and can see rot of
the sill board happening. What can I do BEFORE I replace the siding
and trim to keep water from running under the siding and trim and
rotting it AGAIN and further rotting out the sill board, etc?

Wow, that is a dumb design... I'm surprised it has lasted this long.

My in-laws house had a similar problem, where the basement extended out
under the front and rear porches. As you would expect, water leaked in on
the porches and rotted the sills, joists, and beams supporting the house.
We solved it by doing away with the porches and extending the house out
to the edge of the foundation.

http://www.mountainsoftware.com/proj...009porches.htm

You could probably do something similar by extending your house out to
the edge of the slab.

If you don't want to add square footage, you might be able to cut the
slab back an inch or two from the wall (as close as you can get with a
concrete saw). Then you could add strapping to the outside of the walls
so your siding could overlap the new edge of the slab. I would remove
remaining part of the slab outside and regrade the yard away from the
house. Or pour a new patio at a lower level, sloping away from the house.

The only other option I can think of would be to cut a trough around the
perimeter of the house and install continuous drains. These are often
installed in front of garage doors to keep water from running into a
garage when the drive slopes toward the garage. It wouldn't stop
splashback off the slab, and some water could still find it's way in
under the sill, but it would reduce the volume.

Tricky problem. Good luck!

Anthony Watson
www.mountainsoftware.com/anthony.htm