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STRUCTURAL WOOD ASSESSMENT
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Rot resistant deck & porch lumber choices: this article discusses choices of rot or decay and insect-resistant deck framing lumber as an alternative to using pressure-treated or preservative-treated wood. This article series discuss best porch & deck construction practices, including choice of framing materials, decking or flooring choices & installation, how to select and use deck and porch structural and flooring fasteners, actual deck & porch framing construction details & connections, deck joist & beam span tables, how to build leak-proof rooftop decks, construction of covered & screened porches, deck & porch railing construction & materials, choices of finishes and stains for decks & porches, and past & current deck lumber preservative treatments with related health & environmental concerns.
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As described in Best Practices Guide to Residential Construction, Chapter Four, Best Construction Guide for Building Decks and Porches:
For a price, redwood and cedar are available in structural grades. How rot-resistant the untreated wood is depends on the amount of extractives in the wood, which is greatest in the heartwood cut from dense, old-growth trees.
To purchase all-heart, structural-grade redwood or cedar, expect to spend two to three times more than for pressure treated lumber. It is also difficult to find away from the West Coast. Left untreated, even the heartwood of these species is not recommended for ground contact.
Guide to Plastic Alternatives for Deck & Porch Construction
Structural lumber products made of recycled plastics are starting to make their way into the marketplace and are turning up as railroad ties, dock components, and park walkways. Since there are few standards available for these products, designers and installers will need to rely on manufacturer data for structural characteristics.
One product, TriMax (TriMax of Long Island), is made of recycled plastic and fiberglass and has compression and horizontal-shear strength similar to treated yellow pine. Like most plastic products, however, the material is more flexible than wood due to a low modulus of elasticity. This means spans must be small and the structure may have a bouncy feel.
Choices of Deck & Porch Surface & Flooring Materials
Horizontal deck surfaces take a beating. Rain and snow, exacerbated by wet-dry and freeze-thaw cycles, open up widening cracks, and ultraviolet radiation breaks down wood surfaces. The more sun exposure and water a deck sees, the quicker it will deteriorate. In addition, foot traffic makes it hard to maintain protective finishes.
In choosing a decking material, look beyond its short lived original condition to its appearance and maintenance needs down the road (Table 4-3 just below). In all cases, use the best grade of material you can afford. With wood decking, select tight, straight grain, few if any knots, and low moisture content.
[Click any image or table to see an enlarged, detailed version.]
Since most wood decking materials are graded only for appearance, the grading is unregulated and grade names may be confusing. It is best to see a sample before committing to a purchase.
Choosing Pressure-Treated Wood for Decks
Our photo (left) of severe and dangerous structural rot at a New York deck explains why using rot-resistant lumber to build deck structures and floors is appetizing. The owner tried painting this deck as it began to rot. It didn't help much.
Pressure-treated decking is still the most common choice due to its low cost and ready availability. As with other pressure-treated lumber products, CCA has been phased out in favor of wood treated with copper quat (ACQ) and copper azole (see Preservative-Treated Framing Lumber).
Most builders in the eastern United States choose nominal 5/4 x 6 radius-edge decking (RED), which is dressed to 1 inch thick and can span 16 inches.
Western softwoods are typically sold as 2x4 or 2x6 stock and can span up to 24 inches. For fully exposed decks, particularly those with south-facing exposure, use the best grade available, generally called Premium in southern pine and Patio 1 or Dex in Western species. The radiused edges on RED stock make an attractive deck surface and help prevent splintering.
Many homeowners become disappointed with pressure treated decking when they discover that it must be treated regularly to prevent cupping, checking, and warping. Except where the decking is under a roof and well protected from sun and rain, it must be treated with a water-repellant sealer or a semitransparent penetrating stain to prevent problems.
It is important to finish the wood as soon as the surface is dry but before it has a chance to start cracking, allowing water to penetrate and do additional damage (see DECK FINISHES COATINGS PRESERVATIVES) A few premium products come factory pretreated with a sealer that has penetrated the wood surface and should outlast on-site sealing.
Decay-Resistant Species for Deck & Porch Floor Surfaces
Until the recent introduction of synthetic decking materials, the only viable alternatives to pressure-treated lumber were naturally decay-resistant wood species, such as redwood and cedar. A number of tropical hardwoods are now available to deck builders as well.
Redwood and Cedar Deck & Porch Flooring
The most decay-resistant materials are cut from the dense heartwood of old-growth trees, which is expensive and increasingly rare. In redwood, the lighter colored sapwood offers moderate resistance to decay.
Cedar sapwood is even less resistant. If possible, choose all-heart grades for exposed areas (see Figure 4-1 at left).
The two most commonly used cedar types are western red cedar and Alaska cedar, sometimes sold as Alaska cypress. Western red cedar is relatively soft and easily dented, but dimensionally stable. Yellow cedar is stronger and has a harder surface; but it is prone to shrinkage movement, so it is best purchased kiln-dried.
Other less common cedar species suitable for decking include Port Orford cedar, a strong, dense wood from southern Oregon, and northern white and Atlantic white cedar.
Redwood and cedar should, at a minimum, be treated regularly with water repellants to protect against cupping, checking, and cracking.
Even then, the wood will weather to a silver gray like nearly all wood decking products. For clients who want to preserve the original wood color, the best option is to use an oil-based semitransparent stain with pigments that resemble the desired color.
Our photo of decay at a cedar deck (above/left) shows the condition of a rot-resistant structure after 20 years in a shaded yard with no maintenance having been performed.
Tropical Hardwoods for Deck & Porch Flooring
A number of tropical hardwoods are becoming increasingly available as decking materials, typically sold as nominal 1x4 or 5/4 x6 stock, which can span 16 inches and 24 inches, respectively.
The most widely available hardwood decking now is LPE, a group of dense teak like woods sometimes marketed under the brand name Pau Lope and reported to have a life expectancy in outdoor use of up to 40 years.
Another option for rot-resistant deck construction, Cambara, is somewhat less dense and lighter in color than Ipe, but it also offers excellent resistance to decay and insects [and was recommended in Best Practices]. Both Pau Lope and Cambara are typically knot-free with a tight grain pattern that helps keep out water.
Brazilian wood species recommended for deck construction: Cumaru, IPE, Itauba, Tatajuba, Jarana, Muricatiara, Macaranduba
Thanks to a Brazilian reader who is a deck builder we are informed that there are better choices for rot resistant deck construction:
[Mr. Roda represents Rhodmann Hardwood Flooring, a Brazilian supplier whose contact information we provide below at References. - Ed. We note that the wood species recommended by Mr. Roda may not all be available in North America]
They are strong, dense, and highly resistant to decay and insects, making them ideal for deck surfaces. In general, these woods will outlast the redwood and cedar available today and should require only periodic treatment with a UV-blocking water repellant or a penetrating oil finish such as Penofin (Performance Coatings Inc.). Like most hardwoods, Ipe and cambara cut slowly and must be predrilled for screws.
A third tropical hardwood group, sometimes marketed as maranti, is more commonly known as lauan or Philippine mahogany. This wood offers moderate resistance to decay and insects and requires periodic treatment with a water repellant preservative.
With all tropical hardwoods, there are valid concerns about the wood’s origin and the impact of its harvesting on the world’s rainforests. Fortunately, there are established third-party certification organizations that track the “chain of custody” of hardwood products and certify that they were harvested using sustainable logging practices. Contact the Forest Stewardship Council or the Smartwood Program for more information (see Deck & Porch Products, Manufacturers).
-- Adapted with permission from Best Practices Guide to Residential Construction.
Also see Preservative-Treated Framing Lumber and see Deck Nails, Screws, Hidden Fasteners and see New Preservatives and Corrosion where we describe structural fasteners designed for use in pressure-treated lumber.
At Synthetic Deck Lumber: Composite, Plastic, Vinyl we discuss wooden deck board alternatives such as Trex®, TimberTech®, wood-plastic composites, and plastic or vinyl decking products. This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Also see ourreview of that book.
Green link shows where you are in this article series.
Deck & Porch Resources, Products, Manufacturers: Where to Buy
See Deck & Porch Products, Manufacturers for our complete/updated listings of manufacturers of porch & deck products, materials, coatings, fasteners, lumber, tools.
Deck & Porch Wood Treatment Companies
Arch Wood Protection www.wolmanizedwood.com Copper-azole and borate-treated wood products with optional water repellent
Osmose www.osmose.com ACQ- and borate-treated wood products with water repellent
Chemical Specialties www.treatedwood.com ACQ-treated wood products with optional water repellent
Suppliers of Composite Structural Lumber for Decks & Porches
U.S. Plastic Lumber, Boca Raton, FL www.usplasticlumber.com Trimax and Durawood structural plastic lumber
Composite Decking System Suppliers
Certainteed Corp. www.certainteed.com Boardwalk solid composite decking with hidden fasteners and optional railing system
Composite Building Products International www.xtendex.com Xtendex hollow composite decking system with optional railing
Correct Building Products www.correctdeck.com Solid composite decking with hidden fasteners and optional railing system
Fiber Composites www.fibercomposites.com Fiberon solid composite decking and optional railing system
Kadant Composites www.geodeck.com Geodeck hollow composite decking and railing system
Kroy Building Products www.kroybp.com Timberlast solid composite decking with optional hidden fastening system
Louisiana-Pacific Corp www.weatherbest.lpcorp.com. WeatherBest solid composite decking, railings, and accessories
Nexwood Industries Limited www.nexwood.com Hollow composite decking and railing systems
Tendura www.tendura.com TenduraPlank solid tongue-and-groove composite flooring for porches; natural finish or primed for painting
Thermal Industries www.thermalindustries.com Dream Composite solid tongue-and-groove composite decking system with optional vinyl railings
TimberTech Limited www.timbertech.com Floorizon hollow composite decking system, solid composite decking planks, and optional railing system
Trex Company www.trex.com Solid composite decking
Weyerhaeuser Building Products www.choicedek.com ChoiceDeck solid composite lumber and optional railings
Hidden Deck Fastener Suppliers
BEN Manufacturing www.premier1.net/~ben69 Dec-Klips fit between deck planks with prongs into edges; nailed into top of joists; electrogalvanized steel
Blue Heron Enterprises www.ebty.com Eb-Ty UV-resistant polypropylene biscuit fits into slots in edge of decking, screws into top of joist Grabber Construction Products www.deckmaster.com Deckmaster angle bracket screws to side of joist and up into decking; available in galvanized or stainless steel
Simpson Strong-Tie www.strongtie.com DBTC deck ties screw down to top of joist with prongs into edges of decking planks; triple-zinc-coated or stainless steel by special order; disposable plastic driving tool
Spotnails www.spotnails.com Tebo stainless-steel fasteners fit between decking boards with prongs into edges of decking; installed with mallet and proprietary tool
TY-LAN Enterprises Inc. www.shadoetrack.com Shadoe Track angle bracket nailed along top of joist and screws up into bottom of deck boards; available in galvanized, powder-coated, and stainless steel
USP Lumber Connectors www.uspconnectors.com Deck Clip screws into edge of one decking board and locks to next board; requires toenailing one edge of each board
Sources of Deck Finishes, Stains, Preservative Coatings
Amteco www.mfgsealants.com/amteco.htm Sealers, preservatives, and deck stains
Cabot www.cabotstain.com Clear sealers and deck stains
Cuprinol, a division of Sherwin Williams www.cuprinol.com Sealers, preservatives, and deck stains
The Flood Company www.floodco.com Clear sealers and deck stains
Penofin www.penofin.com Lightly tinted oil-based sealers and stains
Olympic, PPG Architectural Finishes www.olympic.com Clear sealers and deck stains
Wolman Wood Care Products, division of Zinsser Co. www.wolman.com Wolman sealers and deck stains and DAP Woodlife clear sealers
Deck & Porch Industry Associations
American Wood Preservers Association (AWPI) www.awpa.com
California Redwood Association www.calredwood.org
Deck Industry Association www.deckindustry.org
Forest Stewardship Council www.fscus.org Information on certified tropical hardwoods
Rainforest Alliance, Smartwood Program www.rainforest-alliance.org Information on certified tropical hardwoods
Southern Forest Products Association www.sfpa.org
Southern Pine Council www.southernpine.com
Western Wood Products Association www.wwpa.org
Western Wood Preservers Institute www.wwpinstitute.org
-- Adapted with permission from Best Practices Guide to Residential Construction.
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