Dry Deck Over Living Space
A multilayer cementitious coating provides a walkable waterproof surface with a Class A fire rating
In a past job managing condo associations, I spent a lot of time dealing with damage caused by leaks in decks over living spaces. The damage was often quite spectacular. In one case, a seemingly minor flashing error led to rotted framing below eight decks. It cost $114,000 to repair the decks and structural members. That episode convinced me there was a future for contractors who knew how to properly waterproof decks, so I went to work for a coating company. A few years later, I opened my own deck waterproofing business in Arroyo Grande, Calif.
There are about a dozen cementitious waterproofing systems that can be applied over wood framing. They are distributed primarily in the West, a region where there is significant demand for fire-rated waterproof decks. We use a product called Desert Crete (Hill Brothers Chemical Co., 800/994-8801, desertbrand.com), because its maker has been in business for 80 years and its products have a good track record.
Desert Crete is a multilayer cementitious system whose main components are polymer modified cement and a fiberglass-reinforced acrylic resin membrane. The waterproof membrane is sandwiched between layers of the cement, which provides a tough and durable Class A and one-hour fire-rated traffic surface when installed to the manufacturer’s specifications.
That three-layer sandwich is then covered with a suitable finish material. If the framing below is sufficiently stiff, Desert Crete can be used as waterproofing under tile or stamped concrete. More typically, though, we apply a colored textured coating. Although the project described here involved new construction, we frequently install the product on existing decks provided that the framing and sheathing are in good condition.
Get better performance from your deck covering by using ‘best practices’ framing and flashing details
My company specializes in repairing and waterproofing failed balconies, stairs, and roof decks, so I see on a near-daily basis the results of water intrusion into wood framing, especially in mass-produced housing. The costs can be astronomical: For example, recently a simple $3,800 deck repair turned into a $120,000 project, thanks to dry-rot damage to the framing, shear walls, and decks.
That’s unfortunate because building a reliable, long-lasting waterproof deck over living space is relatively straightforward when the best practices and materials are used.
There are a number of ICC-ES–listed manufacturers of Class A walking deck systems (see Class A Fire-Resistant Walking and Roof Deck Systems, sidebar). We’ve installed most of them, and while installation details vary slightly from product to product, none of them will last over the long term if the deck covering isn’t applied over a sturdy substrate.
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Ensuring Balcony Durability: Waterproofing details that stand the test of time
by David H. Nicastro, PE, and Marie Horan, PE
Wood-framed balconies experience a high rate of failure: leaks, visible damage on the finishes below, and, worst of all, concealed structural damage from continued water migration. By the time structural distress becomes evident, it may be too late to implement waterproofing remedies alone—countless wood-framed balconies have required replacement because of severe rot.
The durability of wood-framed balconies widely varies. There are subtle but important differences between the construction of balconies that function for the building’s design life and those that prematurely fail.
Balconies have many of the same details as other portions of the exterior building envelope, but there are also challenging details specific to this type of construction—topping slab edges, column penetrations, door sills, and handrail connections. They are vulnerable to decay because they catch rainfall and direct it to myriad intersecting planes.
Conventional balcony construction, consisting of a concrete topping slab over a waterproofing membrane over wood framing, is prevalent in multi-family residential construction, and it is also used in houses and some commercial properties. Wood rot of balcony framing is a well-known risk, but it is even more widespread than recognized. The authors made excavations into more than 200 balcony soffits in apartments built over a 10-year span, and found undetected water damage in more than 40 percent of them. Additionally, the visible detailing was reviewed on over a thousand balconies, and destructive evaluation and water testing were performed on selected ones.
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A kitchen bump-out provided the perfect opportunity for a small terrace off the master bedroom
“If you want to save cash . . . flash”
“Don’t be a dope . . . slope”
We are adding balconies to everything and people are forgetting that balconies are more than decoration but also have to function. And when we get it wrong it can be catastrophic2.
We are going to be dealing with wood balconies due to their popularity and because they tend to get done wrong more often than concrete and steel balconies.
Aside from the obvious structural engineering issues dealing with water is the number one issue.
With any balcony, getting the water off of it is a big deal. You need to drain the rain. Let me repeat, you need to drain the rain. Balconies need to slope to provide drainage. How much? One-quarter inch per foot works. When you slope the balcony deck the water goes over the balcony edge and the edge needs a drip function. And where the edge meets a wall it needs to terminate in a gutter or a “kick out”. If you do not provide a drip edgewater stains the surface of the balcony face. Not a very good aesthetic result. It can also allow the water to wick inward.
It gets interesting3 when the balcony “traffic surface” is a concrete toping or tile set in concrete. There are two fundamental approaches to “waterproofing” a balcony deck. The first is where the waterproofing layer is exposed and also is the traffic surface. The second is where the waterproofing layer is covered over by a traffic surface. Wherever the waterproofing layer is covered it is critical that a drainage layer or space is provided immediately above the waterproofing layer. I do not use the word “critical” lightly. How big/deep/thick this drainage layer of space should be is open to debate. I typically recommend 3/8-inch. Note that concrete toppings are not waterproofing layers. And coating them with sealers does not turn them into waterproofing layers. READ THE REST BY CLICKING HERE http://buildingscience.com/documents/building-science-insights/bsi-093-all-decked-out