You may have family, friends and neighbors who may be concerned about their own balconies or decks. … Reassure them that the building codes used to design their balconies and decks are adequate.
Few engineers held the code requirements or structural design of the Library Gardens balcony in suspicion, even before seeing photos of severely decayed wood structural members. Design requirements and methods for cantilevered balconies are relatively simple; unfortunately, flashing and water-proofing details are not.
My engineering practice has focused on wood-framed construction for 25 years. Prior to that I built or remodeled wood-framed buildings between college episodes. I have roofed or re-roofed six houses, and replaced or installed new windows and exterior doors. I have repaired faulty construction installed by others. One thing I can say with certainty: The only water-proofing system I would trust to work is one that I installed myself. I do not claim to be a water-proofing specialist, nor do I claim to be the only person who can effectively install flashing—just that I do not find the odds favorable for a good installation by average trades workers. (Whether the lack of skill or caring in the general workforce is due to inadequate training or unwillingness of developers to pay for trained workers is beyond my influence.)
Over the years I have observed or encountered the following:
- Roofing installers relying on black goop (rather than good flashing practices) to waterproof around roof penetrations.
- A 65-year-old contractor who told a client “you don’t want to add a skylight to your house—they always leak.” (I have personally installed eight skylights in my own or relatives’ homes, and none of them have leaked.)
- Sheet-metal roofing installed with a “reverse-lap” (where water running down the roof would flow directly under the down-slope piece of roofing); this was on a public works job, and the general contractor refused to admit that the installation was improper.
- Rotting wood members supporting untold numbers of porches, decks, and stairs.
- Specialty building material suppliers who did not know the common uses of water-proofing products they sold.
- A local contractor who resisted replacing a rotted joist because most of the cross-section remained, even though the decayed wood could be clawed apart with one’s fingernails.
Independent home inspectors see faulty waterproofing over balconies with disturbing frequency—perhaps the majority of the time—rather than as isolated incidents. A local independent home inspector recently reported that a patio over a garage was not properly water-proofed. His claim was met with belligerent opposition from the contractor who had just completed the installation. The contractor provided photos taken during construction, expecting to justify his position; the photos showed blatantly incorrect installation of the water-proofing system.
In many cases inspectors cannot see structural members because they are fully enclosed (often with no venting that would allow wood to dry out in the case of faulty water-proofing, as was the case with the balcony that collapsed in Berkeley). Independent home inspectors pointing out possible leaks based on subtle signs are frequently ignored. Sometimes they are told to keep their suspicions to themselves, as hidden damage is “only speculation.” Perhaps their concerns will be brushed aside less easily now—but the general public has an amazingly short collective memory regarding structural failures or disasters.
The Berkeley balcony collapse had little to do with the structural requirements in the building code. When our designs rely on water-proofing systems that are designed by others, and installed by people who admit not being able to install leak-proof skylights, using materials from suppliers who do not know what they are selling—and these are some of the better circumstances—then we need to change our designs so they will more likely survive water infiltration.
Wood decay is extremely insidious. By the time a trained specialist can detect decay under a microscope, the wood has lost as much as half of its strength. Decayed wood fails in a sudden, brittle manner. If any sign of mold (white or brown fungal growth streaks or “blisters”, etc.) are visible on a member it should be replaced. A simple but effective test for fungal decay is the “pick test”. (Demonstration video showing the pick test.).) To perform the pick test, force a pointed tool into the face of the wood member at about 30 to 45 degrees from the member’s surface. Pry up a sliver of wood. If you can pry up a long sliver that breaks free an inch or so away from the tool and makes a distinct splintering noise, the wood is sound at that location. If the wood breaks quietly and easily right over the tool, this indicates decay is present and the member should be replaced.
The City of Berkeley is considering proposed code revisions for balconies in response to the collapse; most of these affect “architectural” features of balconies . Suggested changes relate to venting, inspection, decay-resistant materials, and maintenance. One revision would require “naturally durable or preservative-treated lumber” for exterior balconies. Preservative-treated lumber presents its own serious problems with fastener corrosion, which, even though currently not widely known to the design and construction professions, could lead to sudden failures on their own.
If we are talking about code changes, I suggest that balconies in dangerous locations (for example: greater than a particular height, or above building exits, assembly areas, or other decks or balconies) be required to have exposed structural framing that can be easily inspected and maintained. This would introduce some slight complications when fire-resistive construction is required. Another option might be requiring steel framing, with the hope that even compromised steel members would fail in a ductile manner. Let’s not wait for code changes before improving our design practices. Consider the following when designing an exterior deck or balcony:
- Longevity of your structural components depends on water-proofing that is commonly designed and installed by others.
- Flashing details become extremely complex—almost to the point of being impossible to show on two-dimensional drawings—when more than two planes meet (such as at door openings, deck extensions, or inset corners).
- Metal flashings often must be soldered together. This is best done in a shop, and requires planning that an unsophisticated contractor may not provide, or scheduling that a fast-track commercial project may not accommodate.
- Architects often show simple, typical flashing details, but do not always detail how to waterproof around door openings, railing connections, etc. Flashing for the failed balcony likely could not have been shown adequately with fewer than eight or ten details.
- Sometimes no flashing details are provided at all, but a general reference to “The SMACNA* Manual” or similar appears in the project specifications. When construction progresses to sheet-metal installation but no SMACNA Manual is on site, will this specification lead to a proper installation? You should inquire whether the architect will include all flashing and water-proofing details on the plans, rather than only referencing a third-party manual. *Sheet Metal and Air Conditioning Contractors’ National Association.
- Properly fabricated sheet-metal flashings for a custom home cost in the range of $30,000. This explains why “flashing-in-a-tube” (in other words, caulking that will probably fail within a few months) is often substituted for real flashing.
- Wood preservative treatments currently used to prevent decay contain high copper concentrations that cause accelerated corrosion of steel fasteners under moist conditions.
- Flashing, water-proofing membranes, counter-flashing, siding, and roofing must often interweave to provide a proper installation. The coordination between trades to accomplish this is not trivial.
- Coefficients of thermal expansion for sheet metal, wood, and water-proofing materials may differ by an order of magnitude or more. This can result in daily stress-reversals where membranes adhere to metal components, leading to eventual loss of seal.
- Gravity is more reliable than sealants.
- “Hot-mopped” tar is a 17th century technology that does not belong in any modern water-proofing system.
- Developers may not be accustomed to paying for materials and skilled labor to properly waterproof exterior balconies, and may be tempted to skimp on water-proofing installation.
- Manufacturers of water-proofing membranes almost always require the substrate to slope a minimum of ¼ inch per foot to drain.
- A complete water-proofing system should include at least the following (working upward from the decking, which the engineer often views as the last part of his or her responsibility): Water-proofing membrane and required primer or adhesive; drainage mat to provide a capillary break and promote movement of water toward a drain or balcony edge; protective surface that may include pavers, mortar bed and tile, poured concrete, etc.
- Contractors and suppliers may substitute specified water-proofing products and provide incompatible materials.
- Workers installing the water-proofing system probably do not understand capillary action.
- Municipal inspectors rarely observe all components of the water-proofing system as they are installed, and likely observe only representative locations rather than each and every location in a project.
- The completed construction may be entirely concealed and impossible to inspect during the life of the building.
- Even if construction is exposed for occasional inspection it may only be inspected at time of sale—and independent inspectors’ possible concerns about damage may be downplayed or ignored.
- Before any building is completed, Mother Nature is already trying to destroy it; she will always win, it’s just a question of when.
Finally—we should not reassure anyone that their balcony or deck is “safe.” We might say that a balcony or deck was probably safe at the time it was constructed. More importantly, we should advise anyone with an exterior deck or balcony that they should have it inspected.
Thor Matteson, SE