Checking into Decking

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by Planning Technician Carol Borck

Yin-Yang deck

There are a lot of decks in Portola Valley, and for good reasons. Decks get us outside to relax in the fresh air, to barbeque and entertain, or to just listen to the birds; Portola Valley is perfect for this. Permits seem to come in daily for new decks, deck repairs and rebuilds, and deck expansions. How are these decks primarily constructed? Out of wood...but there are other options.

Certainly, most people would agree that natural wood with its rich colors and grain variations is the most aesthetically appealing decking surface. Wood is beautiful and versatile, it effectively disperses heat, and can last for years when maintained properly. However, wood does indeed require periodic maintenance and treatments with sealants and preservatives which can be costly and time-consuming, and while wood is a renewable resource, it would have to be harvested from a sustainable forest to be considered a good green product. With these factors in mind, many homeowners are choosing to build their decks with alternative materials.

Since the early 1990's, the synthetic decking market has rapidly expanded (and improved) with viable alternatives to traditional wood. The most common alternative decking materials are 100% vinyl and plastic/wood composites. Generally, these products are low-maintenance and durable, but there are points to consider when choosing materials for your next deck project.


Vinyl decking systems usually consist of 100% virgin plastic (PVC). These decks are perhaps the best option in terms of the least maintenance and they are recyclable when replaced. They are durable, UV protection treated, and retain their color year after year; they will look the same 10-15 years after installation. Vinyl decks require no sealant treatments, they are embossed for slip resistance, and hosing them down will easily clean the stain resistant surface. However, vinyl is highly reflective, retains heat, and the lighter colors show dirt and dust much easier than other decking. Additionally, colors are limited and typically include white, tan, and gray which do not meet the reflectivity requirements for the Town of Portola Valley.


The market of deck components manufactured from plastic and wood is rapidly growing. These products contain a mixture of plastic and wood/cellulose in varying amounts with varying percentages of recycled content. Many have up to 50% cellulose content, and some claim as much as 70% cellulose. Some are 100% recycled content, others are a mix of virgin and reclaimed materials. One popular brand states that it is made of recycled plastic grocery bags, reclaimed pallet wrap, and waste wood, both post-consumer and post-industrial. It is formed in content of about 50-50 plastic and wood.

Composite decking materials are manufactured by a compression molding process; the plastic and cellulose are combined and extruded under high pressure and temperature to form planks and components. Because they contain wood, they are prone to rot if they are not treated with a preservative. Wood fibers in some composite products are not completely surrounded and sealed within the plastic - the fibers can be seen at the surface and cut edges, and they are connected to each other throughout the material. Water can soak into the material and cause rot in those products not containing a preservative. The most common preservative used is zinc borate which lasts up to 20 years and fights rot-producing fungi and inhibits mold growth.

GrainContaining wood, composites are designed to mimic the look and feel of natural wood. Manufacturers offer multiple grain patterns, and color selections include "redwood," "Pacific cedar," "weathered wood," and multitudes of brown and gray hues. The color runs through the depth of the plank, helping hide scratches and wear; however, composites are prone to fading over time. Some manufacturers state that "minimal" fading can be expected - similar to the aging process of natural wood.

The predominant attractions of choosing a composite deck are that they are very durable and low maintenance when compared to natural wood. These decks are more dense than wood, resistant to warping and splintering, and designed to withstand all weather and climate conditions. They do not need sealants or stains for protection against the elements. Upfront costs for a composite deck are generally higher than for wood; however, payback comes through over the deck's lifetime from not having to continually treat it. Although these decks are somewhat stain resistant, oil, grease, berries, rust, etc., do need to be treated as soon as possible, and while these stains may lighten with treatment, they may leave permanent discolorations. Product warranties are generally 10 to 25 years depending on the manufacturer, and the decks themselves can last as long or longer than a traditional wood deck.

view of cut boardComposite decking materials can be worked with as similarly as wood using standard tools. Following exact installation instructions is crucial as daily temperature fluctuations cause slight expansion/contraction of the material, and therefore, board gapping is required. Support joist placement is also very important. Basically, following the manufacturer's guidelines will ensure the deck is constructed properly; your contractor should be knowledgeable of these decks and installation procedures.

All of this in mind, a durable, recycled content deck is a great green choice. If your twenty-year old wood deck is due to be replaced, consider an alternative - it may be right for you!

Disclaimer: The products pictured in this article do not constitute an endorsement, approval, or recommendation of the product by the Town of Portola Valley. These product images are provided only for informational purposes and as visual examples.

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