List of Unusual Problems

Problem #02:
Four-story Tower with Water Leak in Ground Level Baseboard

Magnolia Plaza Apartments
630 Baden Ave
South San Francisco CA USA
April, 1998

(All jobsite directions such as left or right, are with the viewer facing the property from the street or in front of the front entrance.)

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The Simpson Company made a thorough inspection of the outside and inside of the roof and walls of the top floor and the outside of all other floors.

We have discovered several problems, one or more of which are probably causing the leak in question.

(A)  The construction technique used for this building eliminated the wood sheathing and waterproof vapor barrier usually used in building construction.

A-1)  In most stucco and wood frame buildings, plywood sheathing is fastened onto the wall studs, then tarpaper or other moisture barrier is applied over the wood sheathing.  Metal lathe or wire mesh is applied over the tarpaper.  Next a base coat of stucco is applied over the wire mesh and tarpaper, whereupon a final coat of stucco completes the construction.

A-2)  On this building, economy was obtained by eliminating the wood sheathing and tarpaper.  The stucco is applied directly to stucco panels fastened to the wall studs with only a layer of one-eighth inch foam, sandwiched between two layers of Kraft-paper, inserted between the stucco surface and the wood framing.   (On the East & West walls, plywood sheathing was installed on the inside of the studs, perhaps as an attempt at earthquake proofing, although the nailing pattern is sparse for that purpose.)

A-3)  The stucco material is absorbing moisture from the exterior surface and becoming wet throughout.  The inside surface of the stucco material is passing the moisture to the outside facing layer of Kraft paper on the foam sheet via molecular attraction.  The foam liner sheet is stopping the horizontal movement of most of the moisture.  Water stains show this moisture to be coagulating into droplets.   Gravity is drawing the moisture downward three-stories, accumulating more moisture along the way, until the moisture forms rivulets which pool on the sole plate inside of the walls of Unit 11.

These small pools of water seep out under the baseboard to saturate the edges of the carpeting.  Molecular attraction draws the water several feet into the room carpeting.


B)  This moisture problem is inherent in the architectural design of this building.

There are two immediate steps that can be taken to attempt to eliminate the water leak in Unit 11, although these steps will not alleviate the moisture problem inherent in the building design.

B-1)  Step 1 would be to seal up the horizontal expansion joints in the stucco exterior. Normally these joints would not be leaking but the lack of weatherproofing obvious in this structure implies that there could easily be a deficiency in these joints.  This is an inexpensive repair and may help to substantially reduce the moisture reaching the inside of the stucco wall.

B-2)  Step 2 would be to extirpate two horizontal openings in the stucco wall; of three inches or so height and five feet or so width adjacent to the exterior corner in question.  These openings would be about one inch above the sole plate of the exterior walls.  We can examine these openings during the next rain to detail the severity of the leaks.

B-3)  Step 3 would be to manufacture a custom designed splash pan or water diverter to insert into the new openings to catch the water and funnel the water to the outside where it will drop harmlessly to the ground.


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