How to Specify Tropical Hardwood Decking for an Architect's Commercial Project Documents

What a Commercial Decking Specification Must Define

A commercial decking spec has to define the material, the performance, the assembly, and the review process in one coordinated section, because a gap in any one of them surfaces during construction or on the submittal. Architects who specify only the species, and leave grade, moisture content, fastening, and sourcing implied, are the ones who field questions after the bid or discover a substitution on site. The WoodWorks technical resources for commercial wood construction make the same point: exterior wood is a system, and the specification has to describe the whole system, not just the wearing surface. The sections below take those pieces in order, starting with the one every spec gets half right: the species and its grade.

Species and Grade in Real Terms

State the species and the grade in recognized grading language, not adjectives, since \"premium Ipe\" tells a supplier nothing enforceable. Name the species (Ipe, Cumaru, Garapa, Massaranduba) and reference the applicable NHLA grade or an architectural grade defined by an approved sample. Specify grain orientation where stability matters, since vertical-grain boards move less than flat-grain. Because color varies by species, note whether color sorting is required, which matters on continuous commercial surfaces where lot-to-lot variation is visible. A grade the supplier cannot grade to is not a grade.

Defining grade by sample is the enforceable path: a physical sample sets the color range, grain, and defect expectation the supplier grades to. This protects both the owner and the specifier and is standard on architectural work. Grade settles how the deck looks. The performance criteria settle what it must do.

Performance Criteria for the Decking Spec

Specify the measurable performance the deck must meet: durability class, fire rating where the code requires it, and the moisture content at delivery. Tropical hardwoods rate Class 1 durability under EN 350 and reach Class A flame spread under ASTM E84 without treatment, which matters on commercial rooftops and assemblies with a fire requirement. Require the boards kiln-dried to a stated moisture content, roughly 12 to 16 percent, so they do not move after installation. These criteria give the submittal reviewer objective measures to check rather than a subjective description. With the numbers fixed, the next decision is physical: the board profile and the fastener that holds it down.

Profile and Fastener Method as One Decision

Specify the profile and the fastener method together, because square-edge boards, pre-grooved boards for hidden clips, and pre-drilled boards for plugged face screws are different products. A hidden-fastener deck needs pre-grooved boards milled to a named clip system; a plugged face-screw deck needs pre-drilled and countersunk boards with matching plugs; both need stainless fasteners, 316 near salt water. Specify the fastener grade and the board gap. The American Wood Council publishes the fastener design basis these choices follow. Leaving the fastener method to the shop drawings is a common source of conflict. The boards and fasteners are also only the visible half of the assembly, which is why the spec has to keep going below the surface.

The Substructure, Drainage, and Rooftop Detailing

The specification has to describe the assembly beneath the boards, since a Class 1 deck on a substructure that traps water still fails. Define the joist material and spacing, commonly 16 inches on center for 5/4 boards, the board gap and drainage, and, on a rooftop or balcony, the pedestal or sleeper system that floats the deck above the membrane without penetrating it. Dense tropical decking adds weight, around 5 to 6 lb per square foot for 5/4 Ipe, so the structural load is confirmed. See our rooftop deck systems guide for the membrane detailing.

Documentation the Submittal Requires

Commercial and public submittals require documented legal sourcing: FSC chain-of-custody, CITES permits for listed species, and, on green-building projects, the certification that supports LEED materials credits. Only an FSC-certified supplier can issue valid chain-of-custody, and the U.S. Green Building Council recognizes FSC toward LEED. Write the documentation requirement into the spec so it is priced into the bid rather than discovered late. See our FSC certification guide. Paper proves the sourcing. The sample and mockup, covered next, prove everything else.

Samples, Mockups, and the Submittal Review

Require a physical sample and, on larger projects, a mockup approved before release, so the color, grain, profile, and finish are agreed against a real reference rather than a description. The submittal package should require species and grade samples, the actual milled profile, and the finish on the real species. Reviewing these against the specification catches substitutions early, since a lower-cost species or a similar-looking profile changes shrinkage, finish behavior, and fastener holding. An approved sample also anchors the color sorting for variable species. In practice, when J. Gibson McIlvain supports a commercial submittal, what lands on the reviewer's desk is a species and grade sample, mockup material milled to the specified profile, and the FSC chain-of-custody and CITES paperwork, so the review happens against real material and real documents.

Single-Source Supply Across the Project

Specify single-source supply for the decking package so grade, color, and milling stay consistent across every phase and elevation of a commercial project. On a large or multi-building job, material split across suppliers drifts in grade and color, which reads on continuous surfaces. A single deep, certified source fills the whole project in matched material, mills any custom profiles and pre-grooving in-house, and provides the documentation for the submittal. J. Gibson McIlvain supplies commercial decking from one certified inventory with in-house milling. Consistency across a commercial deck is either specified or left to luck.

Completing the Decking Specification

A complete commercial decking specification reads as one coordinated package where the material, performance, assembly, documentation, and review all point at the same deck. Written this way, the submittal reviewer has objective criteria to check, the bidder prices the real scope including documentation, and the installed deck matches the intent. The USDA Forest Products Laboratory Wood Handbook is the reference behind the durability and moisture criteria. J. Gibson McIlvain supports the specification with samples, FSC and CITES documentation, in-house custom milling and pre-grooving, and single-source supply shipped nationwide.

Coordinating the Decking Section With Roofing and Structure

On a rooftop or elevated deck, the decking specification has to coordinate with the roofing and structural sections, because the deck floats on the membrane and loads the structure. The membrane and its warranty live in the roofing section, the load capacity in the structural section, and the wearing surface in the decking section, and a conflict between them, a fastener detail that penetrates the membrane, a weight the structure cannot carry, surfaces during construction if the sections are not reconciled. Referencing the pedestal or sleeper system, the no-penetration requirement, and the confirmed load in the decking spec keeps the trades aligned. See our rooftop deck systems guide for the membrane interface.

Evaluating Substitution and Or-Equal Requests

Commercial bids often bring substitution or "or-equal" requests, and the specification should define how they are evaluated: against the approved sample and the stated performance criteria, not a name. A proposed alternate species or a similar-looking profile can change durability class, density, movement, finish behavior, and fastener holding, so an "or-equal" is only equal if it meets the same measurable criteria and matches the mockup. Writing the evaluation basis into the spec, durability class, fire rating, grade by sample, gives the architect an objective way to accept or reject an alternate rather than a subjective argument. J. Gibson McIlvain can supply samples and documentation that let a specifier evaluate an alternate against the specified criteria. A species name is not a performance criterion.

Performance Criteria and Their Standards

Each criterion references an objective standard, EN 350, ASTM E84, NHLA, so a submittal reviewer can verify rather than judge subjectively.

"The specs that go smoothly define grade in real language, set a moisture number, lock the profile to the fastener method, describe the substructure, and require a mockup before we ship. When all of that is in one section, the species almost takes care of itself and the submittal clears. The ones that struggle just say premium Ipe decking and assume everyone fills in the rest the same way. On a commercial job the documentation is part of the spec too, not a favor at the end."

Brett Miller, President, J. Gibson McIlvain Company