Walls that rely solely on caulking to keep them watertight have trouble with heavy rain. These walls try to seal out the water, but the caulking always ages and requires maintenance. A wall system that works best has three lines of defense against water penetration. All together we call it a "rain screen" wall. The first line of defense is brick or other siding. This is not totally waterproof. In fact, if you look at brick-veneer walls they have holes at the bottom; vinyl or aluminum siding has holes under every row of siding. These holes serve as vent holes to let air in and out behind the siding to help keep it dry. They also let the air in so that the wind literally blows on both sides of the brick, which means there is little or no wind force to drive water through the brick. The second line of defense is an air space and then a membrane against the wall that sheds water, like building paper. Most of the water that does get past the siding will flow down the back side of the siding. The little that gets across the air space flows down the membrane. And the bottom of the wall is always flashed and drained to the outside. The third line of defense is an air barrier somewhere in the wall that stops the wind so it will not blow into the house. A properly built rain-screen wall is almost always a trouble-free wall.