Unusual Problems: Problem #03

Problem #03:
Hidden Persistent Leak in Fourth-story Walking Deck

The Hamlet Condominiums
4149 F El Camino Way
Palo Alto CA 94306-4035
August 1998

DECK COVERING FAILURE ANALYSIS
(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 fourth-story, texture-coat protected deck area has leaked persistently since being constructed.

Multiple attempts at repair have failed.

The structure was built ten years ago.

The fourth-level deck above the third-story family room of this condominium has experienced severe and continuous leaking since it was constructed ten years ago. This deck with adjoining roofs and corridors has been repaired over a dozen times by several different waterproofing repair firms since construction but the leaking continued. Litigation was occurring. No waterproofing company was able to stop the leaks.

The Simpson Company was called-in to examine the problem in 1998. Our preliminary inspection revealed that the flexible deck system on this leisure-deck was installed over an epoxy-sand mortar built-up to almost one-inch thick in a futile attempt to divert standing water into two small deck drains to stop the leaking. Large cracks up to one-eighth of an inch in diameter in this surfacing were obvious leaks, but we deduced that the volume of water entering these cracks was insufficient to cause the ceiling collapse that had proceeded our being engaged as consultants.

Furthermore, this deck surface itself was one of the unsuccessful attempts at repair of the leaks. Therefore it was possible that the previous deck surface, installed during construction, was not cracked before being replaced. If this was so, then the leaking was occurring even before the current deck surface cracked.

The Simpson Company decided to dismantle the roof tiles, roof felt, roof flashings, deck surfacing, corridor surfacing, corridor-wall stucco surface etc., peeling down until we felt that we discovered the culprit.

This deck has eight different areas of varying construction detail of interest to this inspection:

The overall field area of deck surface.
The field area of the two attached corridors.
The four-story, north-side, perimeter, 24-inch, parapet wall flashing.
The one-story (above landing), south side, decorative, four-inch, parapet wall flashing.
The 10/12-pitch, aggregate-tile, adjoining, roof bottom-eave flashing.
The deck to corridor flashing.
The corridor to wall flashing.
The corridor to exterior wood flush-door flashing.

Details of Inspection Results:

The overall field area, about 500 square feet, of deck surface has large random cracks, which appear to be caused by expansion and contraction of a deck coating installed over a ¾-inch non-reinforced epoxy-sand mortar system. This aggregate has developed cracks up to 1/8-inch wide, which penetrate to the plywood surface below allowing rainwater to contact this plywood.
The field area of the two attached corridors, replaced last year, is showing no visible damage at this time and was not opened for inspection.
The four-story north side perimeter 24-inch parapet wall flashing appears to suffer no visible damage and was not opened for inspection at this time.
The south side, four-inch parapet-wall flashing appears to suffer no visible damage at this time. This purely decorative toe-wall creates a needless water dam. This water dam caused major water pooling during the 1997/98 El Nino storms. The two small (shower drain) deck drains were inadequate to relieve the water backup. This small-volume drainage situation can be relieved with the simple addition of two four inch wide spillways into the two existing rain gutters which contact the underside of the straight toe-wall at each end.
The 10/12-pitched aggregate-tile adjoining roof bottom eave flashing was improperly installed. This lower eave roof-deck plywood ends at a level of 1.5-inches above the texture coated deck surface. The roof deck "L" flashing has a 2.5-inch vertical rise, much lower than the 4-inch parapet wall and yet higher than the adjoining 1.5-inch pitched roof-deck. This flashing should have been an exaggerated "Z" shape with a vertical rise of 1.5-inches and an additional angled run of 7.5-inches to create an effective total height of 6-inches. A bottom roof-tile flashing using a 1-inch leg perpendicular to the sloped roof deck supported the lowest roof tile course. This I-inch step was not provided with weep holes or other drainage, creating an effective water dam. There was no outlet from this water dam. The accumulating water from the tarpaper moisture barrier under the aggregate tiles was forced to seep through the rake end of the flashing at the adjoining corridor sidewall. This water formed a pool on the pitched plywood roof deck i.5-inches above the texture-coated deck in the corner where the corridor intersected the pitched tile roof. This triangular-shaped pool was created by the vertical component of the deck flashing, the vertical component of the corridor deck flashing where the rake of the pitched roof approached within 1.5-inches of the texture coated deck, and the sloped plywood roof deck itself. The more or less constant water pooling in this area engendered fungus damage to the plywood in addition to a constant leak into the inside lower room. Drawing 2-D shows some detail of this flashing.
The deck to corridor flashing was not opened for inspection at this time.
The corridor to wall flashing was not opened for inspection at this time.
The corridor to exterior wood flush-door flashing was inadequate. This door appears to have had some wood cut off from the bottom and not primed or painted. The corridor deck texture coated surface was raised to actually contact the lower edge of this wood flush door, which normally should have been I-inch or more above the deck surface. The more or less constant contact with a wet deck surface during the rainy season has caused the door to bloom and delaminate at the bottom. Wood fungus was engendered because of this. Termites were welcomed by this easy access and the door area is now infested with both fungus and termites.

Last updated on 28th May 2004.
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