There are a lot of questions swirling around regarding the City of Berkeley’s handling of its investigation into the Library Gardens balcony collapse.

The recent new safety regulations passed by the City Council and believed by Berkeley Mayor Bates to be the toughest in the state, while welcomed, add much fuel to the controversy.

Two conspiracy theories have emerged to explain the City’s haste to demolish the second balcony and turn the evidence over to the owner. The first theory is that the city officials are simply trying to put the tragedy behind them as fast as possible because it calls into question its ability to manage the current building boom. The second theory is that it is to protect the developer by destroying evidence, with the contractor being the fall guy.

That the developer has very strong ties to Berkeley and Bates is very chummy with the developers is well documented. These facts alone do not justify the conspiracy theories.

People interested in construction are also talking. They do not pretend to know what caused the balconies to rot but want to understand the possibilities. One possibility is that the waterproofing flashing was done wrong, or failed, and allowed water to enter the cavity between the top of the deck and its underside feeding the rot. While the planning department has stated that it does not know what led to the rotting of the balcony joists, its recommendation that the building code be changed to require venting, and the ability to inspect the joist cavity, is an important change should the problem be faulty flashing. The City Council is to be commended for its quick action in passing the Planning and Development Department’s recommendation.

Another possibility, that the rot was caused by condensation of water vapor from inside the building, is not as easy to understand. Most of us are familiar with double-pane windows, the kind that after a few years start fogging up between the layers of glass. The fogging is caused by the seal around the two layers of glass beginning to leak air. When the window heats up, with the normal warming during the day, air between the glass expands pushing air out of the failed seal. At night, when things cool off, the air between the glass contracts pulling air in from outside the window. If the air it pulls in has water vapor in it, condensation can happen when the temperature of the window falls. Over time, the condensation can build up inside the double pane window. The technical term for the pulling in and pushing out of the air is thermal pumping.

Think of the balcony as a kind of double-pane window jetting out from the building, sealed all around so rain water can’t get in but with a thin area between the top and bottom of the deck unsealed where the deck attaches to the building. Water can’t intrude from the outside, but air can come into the deck cavity from the inside of the building where the deck is attached to the building. With the changes in temperature between day and night there is thermal pumping. If there is enough water vapor in the air inside the building, on cold nights condensation could occur when the warm moist air in the building is pulled into the balcony joist cavity. The condensation could build up and promote the growth of fungus, rotting the joists and leading to a failure. Remember, this is only a possibility, we don’t know why the Library Gardens balcony joists rotted.

At this point, talk of the condensation possibility usually turns to a whole systems discussion. The questions become how much water vapor is in these buildings. How are the stove, dishwasher, bathroom, and rest of the apartment vented? How is the building’s thermal-envelope designed and what does it look like where the deck attaches to the building? Is there a vapor barrier and insulation where the building and deck join?

People exhale a pound or more of water every night: should we set an occupancy limit so as to keep in check humidity levels in apartments? There is thermal pumping not only outside the thermal-envelope in decks but also in the exterior walls. The wrong conditions can lead to mold. That many recent building have had problems with their thermal-envelop is well documented — is the deck joist decay somehow related? It is the responsibility of the contractors to build according to the plans, and it is the developers responsibility to get the plans right. Are these buildings suitable as designed for the kind of intense occupancy they are being put to?

We can now understand the conspiracy theories. The City says it doesn’t know what caused the rot, but its discussion doesn’t consider condensation of water vapor from inside the building. That Bates thinks the new balcony requirements are tough does not mean they are adequate.

Berkeley should revisit its balcony code changes and look at the possibility of requiring that the thermal-envelope not be interrupted where the deck attaches to the building. Venting of apartments also needs to be studied and probably greatly improved. This is too important not to get right.

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Tim Hansen works as a project manager restoring buildings and has over 35 years experience in construction. He is a former member of Berkeley’s Landmarks Commission and its Energy Commission, and was on the board of the Berkeley Architectural Heritage Association and the Hillside Club.

Tim Hansen works as a project manager restoring buildings and has over 35 years experience in construction. He is a former member of Berkeley’s Landmarks Commission and its Energy Commission, and was on the board of the Berkeley Architectural Heritage Association and the Hillside Club.