How to Specify Tropical Hardwood Decking for Commercial Project Documents

What a Tropical Hardwood Decking Specification Has to Accomplish

A tropical hardwood decking specification works only when a contractor who never spoke to the design team can buy the right material, install it correctly, and pass inspection without filing a single RFI. That is the whole test. Everything else is commentary. Most decking sections in commercial project manuals fail that test for the same reason, which is that they were written as a shopping list instead of a set of enforceable requirements.

Tropical hardwood decking behaves unlike anything else in Division 06. It is dense enough to blunt carbide. It moves seasonally in ways a softwood spec never anticipates. It arrives from South America under legality documentation that a purchasing agent has to read and file. And it sells in a market where one trade name can cover several botanical species with meaningfully different performance. A spec that says "Ipe decking, 5/4x6, clear" leaves the door open to four different outcomes on the jobsite, three of which produce a punch list.

Write the section in standard three-part CSI format. Part 1 covers submittals, quality assurance, delivery, storage, and the mockup. Part 2 names the material with botanical precision, grade, moisture content, profile, and tally. Part 3 governs installation, fastening, gapping, and the substructure interface. Contractors read Part 3 first and Part 2 second. Write both as though that is true, since it is.

Where Tropical Decking Belongs in the Project Manual

Exterior hardwood decking belongs in Division 06 under a wood decking section, not under the composite decking section where a surprising number of firms file it out of habit. That single misfile invites substitution. A section header reading "Composite Decking" tells a value engineer exactly what you will accept.

Coordination matters more than placement. On a rooftop amenity deck, the decking section has to reference the waterproofing and pedestal system sections so that pedestal spacing and joist direction get settled before anyone orders material. On a boardwalk or grade-level plaza, coordinate with the site improvements and structural framing sections, since the sleeper or steel layout determines whether your board span is legal. Where the deck meets a door threshold, coordinate with the flashing and sill details. The most common source of tropical decking failure is not the wood. It is the assembly the wood was fastened to.

Reference the governing structural documents by name rather than paraphrasing them. The American Wood Council codes and standards library holds the National Design Specification and the wood construction documents your framing engineer already uses, and the International Code Council publishes the model code your AHJ enforces. Cite them. Do not restate them in your own words. Paraphrase creates conflict, and conflict creates RFIs.

Species Selection and How to Name It So You Get What You Drew

Specify the botanical name alongside the trade name, or accept that you have specified a category rather than a material. Ipe is Tabebuia spp. Cumaru is Dipteryx odorata. Massaranduba is Manilkara bidentata. Jatoba is Hymenaea courbaril. Garapa is Apuleia leiocarpa. Red Balau is Shorea spp. Teak is Tectona grandis. Trade names drift across regions and importers. Botanical names do not.

Durability class should drive the decision on a twenty-five year civic project. Hardness should drive it on a high-traffic retail plaza. They are not the same axis. Janka hardness predicts dent and wear resistance under foot traffic and dropped furniture. EN 350 durability class predicts resistance to fungal decay in the wet and in ground contact. A board can be very hard and only moderately durable. Specify for the failure mode you actually fear, and if you fear both, say both.

Verify every one of these numbers against a primary source before it enters a submittal package. The USDA Forest Products Laboratory Wood Handbook is the reference of record for mechanical properties, and The Wood Database serves as a fast cross-check on species identity and reported ranges. Published Janka figures swing by several hundred pounds across sources because trees vary. Write a floor rather than a point value if hardness is contractual.

Where a project cannot accept tropical hardwood at all, modified wood is the honest alternate. Thermory and Abodo Vulcan both offer modified decking with real durability gains and manufacturer warranties behind them, and Accoya sits in the same category. All three are limited by kiln size to roughly sixteen feet, with metric lengths landing just under sixteen feet. If your drawing calls for an eighteen foot run without a butt joint, modified wood is off the table, and you want to know that before the alternate goes into the bid documents.

Grade, Dimensions, Lengths, and Tally

Decking grade is a supplier standard rather than a published national grade, so the spec has to describe the face you expect instead of citing a rule number and hoping. The National Hardwood Lumber Association rules govern the hardwood lumber decking gets milled from, and those rules are written for cutting yield in furniture and millwork, not for the appearance of a walking surface. Nobody sells FAS decking. Say what you mean instead. Clear one face and two edges. No knots, no wane, no sapwood on the exposed face. Minor color variation accepted, since the alternative is a spec no mill on earth can hit.

Standard profiles run 1x4, 1x6, 5/4x4, and 5/4x6, and commercial work is written in 2x. Boardwalks, piers and plaza decks are specified at 2x thickness to control deflection, and the precedent is strong enough that no estimator prices a public deck thinner even where 5/4 pencils out structurally. That has a sourcing consequence worth knowing before the species column gets filled in: only Ipe, Cumaru and Jatoba can be sourced consistently in 2x decking thickness, so writing a commercial deck around a species milled mainly for the 5/4 market will strand the spec at buyout. A 5/4x6 board covers about 2.1 linear feet per square foot of deck. Hand that number to the estimator so the takeoff and the tally agree. On a 5,000 square foot rooftop that is roughly 10,500 linear feet before waste, and waste on a diagonal layout is not waste on a running bond.

Length is where commercial specs quietly fail. Random length tally is the default and it serves most decks well. If the design intent depends on continuous boards across a fixed dimension, though, specify it and require a length tally in the submittal. Solid tropical hardwood comes in lengths well past sixteen feet when the design calls for it, which is precisely the advantage it holds over modified product on long runs. Do not assume it. Put it in writing.

Moisture Content and the Movement You Are Designing Around

Specify an in-service moisture content of 12 to 16 percent and require the supplier to certify it at shipment, since every gapping decision downstream depends on that number. Kiln dried to 6 to 8 percent is the right target for interior millwork and the wrong target for an exterior deck. Material that dry picks up moisture, swells, and closes the gaps you carefully drew.

Tropical hardwoods move. Ipe is stable for its density, but it is not inert, and tangential movement across a nominal six inch face is enough to pinch a fastener or cup a board when the assembly gives it nowhere to go. Deliver material to the site and let it sit in the conditions it will live in. Two weeks stickered under cover, out of direct sun, off the ground, with air moving through the pile. Then install.

Gap width follows from season and moisture. Boards installed in a dry winter will swell. Boards installed after a wet delivery will shrink. Write the gap as a range tied to metered moisture content at installation rather than a single fixed dimension, and require the contractor to meter the material and record the reading before the first board goes down. A meter reading costs nothing. Pulling eight thousand linear feet of Ipe costs a season. Building Science Corporation has published the physics of wood and water for decades, and the drying principles that apply to a wall assembly apply to a deck board with the same force.

Profile and Fastener, Which Are One Decision Rather Than Two

The profile you draw determines the fastener you can use, so specifying an appearance and a fastening method independently is how a deck ends up with visible screws the architect never intended. Shiplap takes visible fasteners. Only tongue and groove works with hidden fasteners. Square edge stock gets face screwed. If the rendering shows an uninterrupted field with no fastener heads, the profile has to be tongue and groove or a side grooved board matched to a specific clip system, and that clip system belongs in Part 2 by manufacturer and model.

Pre-drill everything. Tropical hardwood at 3,500 lbf Janka will snap an unpiloted screw or split a board end, and it will do it on the first course. Pre-drill and countersink. Put it in Part 3 so it is not a field preference.

Fastener metallurgy is a specification decision. Use 316 stainless for coastal work without exception. Tropical hardwood tannins are aggressive, salt air is aggressive, and together they will eat a coated deck screw and leave a black stain radiating from every hole across an otherwise perfect field. Inland, 305 stainless is defensible. Plated or coated carbon steel is not defensible on a tropical deck anywhere.

Boards machined with relief grooves on the back face install grooves down so water drains and air moves. Crews reverse this often enough that it belongs in Part 3 as a plain sentence, not buried in a detail note.

"The spec that saves the contractor money is the one that answers the fastener question before the first board goes down. I have walked decks where the profile said hidden fastener and the boards were square edge, and somebody made a field decision at four in the afternoon that the architect lived with for the next twenty years. Draw the profile, name the clip, name the screw, and the deck installs itself."

Norm Moton, Director of Sales, J. Gibson McIlvain

Substructure, Span, and the Airflow Nobody Draws

Dense hardwood decking requires joists at 16 inches on center for standard board thicknesses, and the deck fails from below long before it fails from above. Stretch to 24 inches on center and you get deflection, then fastener working, then squeak, then split. A diagonal layout grows the effective span by roughly forty percent, which turns 16 inches on center into 12 inches on center. Draw it that way rather than discovering it during shop drawing review.

Material goes on furring strips or joists. Never directly on a membrane, never bedded on slab, never set in mortar. The underside of a tropical hardwood board has to dry, and a board that can only dry from one face will cup toward the dry side every time. Rooftop pedestal systems handle this well when pedestal spacing matches the joist requirement instead of the paver module the pedestal manufacturer designed around.

Air has to move. A deck skirted tight to grade with no ventilation is a moisture trap, and the highest durability class in the world will not rescue a board that never dries. Specify a minimum free ventilation area at the perimeter. Skirt boards need to be louvered or held off the ground, and the minimum clearance to grade belongs in the section as a number rather than a note. This one detail does more for service life than the species choice does, and it costs nothing at design time.

Fire Rating, Slip Resistance, and Accessibility

On a rooftop deck, a podium deck, or any assembly occupancy, flame spread is a code requirement rather than a marketing line, and Class A means an ASTM E84 flame-spread index of 25 or less. Ipe tests to Class A, which is one reason it appears on so many rooftop amenity decks in Type I and Type II construction. Do not assume the same for every tropical species. Require the E84 report as a submittal, tied to the specific species and thickness you are buying, and check the report date. The test method is published by ASTM International and the acceptance criteria live in the model code.

Accessibility governs the gap. Under the ADA Accessibility Guidelines, openings in a walking surface on an accessible route cannot allow passage of a half inch diameter sphere, and elongated openings have to run perpendicular to the dominant direction of travel. A deck gapped at five eighths of an inch for drainage is not compliant on an accessible route. That conflict surfaces at plan review if you are lucky and at the certificate of occupancy inspection if you are not. Resolve it in the drawings, not in the field.

Slip resistance deserves a sentence of its own. Smooth tropical hardwood is slick when wet, and grooved face profiles help less than people expect. Where the deck serves a pool surround or an exposed stair tread, specify the surface treatment and require a mockup that gets walked on wet before anyone signs off. WoodWorks publishes technical resources on wood in non-residential construction that help when you are defending an assembly to a plan reviewer.

Legality Documentation, Certification, and the Submittal Package

Every tropical hardwood shipment carries a paper trail, and the specification has to name which papers you want before the material ships rather than after it lands. When using a CITES-listed species, documentation is required at import and the permits have to accompany the shipment. Verify current listings against the CITES appendices directly rather than against any supplier's website. Listings change, and the appendices are the only authority. Lacey Act declarations apply broadly to imported wood products and the importer files them. Ask for that documentation as a numbered submittal item.

Chain of custody is a separate question from legality. If the project chases certification points, the material has to carry a valid Forest Stewardship Council chain of custody claim on the invoice, from a supplier holding a current certificate, and the claim has to survive every handoff between forest and jobsite. A supplier who is FSC certified is not the same thing as a shipment that is FSC claimed. The USGBC LEED materials and resources credits reward the documented claim and ignore the general assurance.

Keep the submittal list short and specific. Physical samples large enough to show real color variation, not chips. A length and grade tally. Certified moisture content at shipment. The E84 report where fire rating governs. Chain of custody and legality documentation. Fastener and clip product data. A field mockup of meaningful area, built on the actual substructure, fastened the actual way, and left to weather long enough to be honest about how the color will move.

Lead time belongs in Part 1. Custom profiles and milled to order work take longer than material pulled from stock, so the real lead time depends on whether your supplier already holds the dimension you drew in inventory. Confirm it rather than assuming it. State the lead time in the spec so the general contractor sequences around it instead of calling about it in week six of a twelve week job.

How J. Gibson McIlvain Would Specify This

Write Part 2 to a floor rather than a wish, and write Part 3 to the failure modes you have actually walked. Here is the shape of a section that holds up under a competitive bid.

Name the material as "Ipe (Tabebuia spp.), clear one face and two edges, free of knots, wane, and sapwood on the exposed face, kiln dried to 12 to 16 percent moisture content certified at shipment." Name the profile and thickness in the same sentence. If hidden fasteners are the design intent, name the clip manufacturer and model in the same paragraph so nobody has to infer it from a detail. Call the tally. If you need lengths past sixteen feet, say so explicitly and require the tally as a submittal. State that substitutions require species identification, an E84 report on the substituted species at the specified thickness, and a durability class citation. That is a fair requirement, and it also happens to end most substitution requests before they start.

Part 3 should read plainly. Joists at 16 inches on center maximum, reduced to 12 inches on center for diagonal layouts. Pre-drill and countersink all fastenings. 316 stainless fasteners on any project in the coastal zone. Boards with back relief grooves installed grooves down. Minimum perimeter ventilation and minimum clearance to grade, both stated as numbers. Acclimation stickered under cover for a minimum of two weeks with a metered reading recorded before installation begins. Gap width per metered moisture content at time of install. Nothing in that list is exotic. All of it gets skipped when the spec stays silent.

J. Gibson McIlvain mills and stocks Ipe decking across the full run of standard and custom dimensions, holding a deep inventory in 1x4, 1x6, 5/4x4, 5/4x6, and 2x6, including the long lengths and wide boards commercial work demands, and ships it by the truckload nationwide, regularly to California. The company has imported and milled hardwood since 1798 and holds FSC certification, so the documentation your submittal package needs travels with the material instead of chasing it. If the section is still in draft, send it over before it goes out for bid. An hour spent checking spec language against real inventory saves a change order later. Call 800-638-9100 for a quote or a specification review, or start at the J. Gibson McIlvain Ipe decking page to see the dimensional range.

Specification Language That Fails in the Field

The most expensive words in a decking specification are the ones that sound reasonable and mean nothing. "Premium grade" has no definition. "Or equal" without acceptance criteria means the cheapest thing on the truck. "Kiln dried" without a number means whatever the kiln was set to that week. "Marine grade fasteners" means nothing at a supply house counter. Every one of those phrases has cost somebody a deck.

Two more worth naming directly. Do not promise a warranty on solid unmodified wood, and do not accept a spec that implies one. Solid tropical hardwood is a natural material graded to an appearance standard, and it carries no warranty from anybody. Modified products such as Accoya, Thermory, and Abodo Vulcan do carry manufacturer warranties, which is a legitimate reason to consider them, just as their sixteen foot ceiling is a legitimate reason long runs stay solid tropical.

Then there is the silver bullet problem. No species solves a deck by itself. Installation carries as much weight as selection, and a Class 1 board on a 24 inch span with coated screws and no airflow beneath will fail faster than a Class 2 board detailed correctly. Get the substructure right. The fastener choice and the airflow underneath matter just as much, and neither one shows up in a rendering. The species choice is the pleasant part of the decision, and it is also the smallest part of it.