What Architects Should Specify When Calling for Tropical Hardwood

Specification Clarity: Getting What You Design

Too many tropical hardwood projects start with a specification that says something like "Ipe decking, per manufacturer's recommendations." This level of vagueness invites problems: material substitution, grade mismatches, incorrect profiles, and installation shortcuts. A proper specification ensures the project receives exactly the material the designer intended.

The Complete Specification Template

A thorough tropical hardwood specification should include:

1. Species: Specify by both common name AND botanical name. "Ipe" alone can refer to multiple Tabebuia species with different properties. The most commonly specified commercial Ipe is Tabebuia spp. (multiple species within the genus). If species purity is critical, specify the exact species.

2. Grade: Select and Better, Standard and Better, or Construction Grade. Define the maximum allowable characteristics for the project: maximum knot diameter, maximum number of pin holes per board, acceptable color variation range, and maximum wane.

3. Dimensions: Nominal and actual dimensions. For decking: 5/4 x 6 (actual 1" x 5-1/2"), or specify exact dimensions. For cladding: 1 x 6 (actual 3/4" x 5-1/2"). Include tolerance specifications for width and thickness.

4. Profile: S4S (surfaced four sides), T&G (tongue and groove), shiplap, or custom mill profile. For grooved-edge boards, specify groove dimensions and the specific clip system they must accommodate.

5. Moisture Content: Target MC at delivery (typically 12–18% for exterior applications). Specify the measurement method and acceptable range.

6. Surface Finish: Smooth-planed, wire-brushed, or rough-sawn. For anti-slip applications, specify the groove pattern or texture treatment.

7. Lengths: Random lengths (most common and most economical) or specified lengths. Random length bundles typically range from 4' to 20', with an average length of 8–12'.

8. Sourcing and Certification: FSC-certified, FSC Chain of Custody documentation required, or no sourcing requirement. If FSC is specified, define whether FSC 100%, FSC Mix, or FSC Recycled is acceptable.

9. Fire Rating: For WUI zones or commercial applications, specify the required ASTM E84 fire classification and require test documentation from the supplier.

10. End Sealer: Specify factory-applied end sealer and field-applied end sealer after all site cuts.

Fastener Specification

Don't leave fastener selection to the installer:

• Stainless steel grade (Type 305 or 316)
• Screw type (trim-head, flat-head, or clip system)
• Screw size (#8, #10, #12) and length
• Pre-drilling requirement (state explicitly)
• Fastener pattern (2 per joist crossing, 3/4" from board edge)

Installation Specification

• Joist spacing (16" OC or 12" OC)
• Board-to-board gap (1/8" or 3/16")
• Minimum ground clearance (18" or 24")
• Ventilation requirements
• Acclimation period (minimum 5–7 days on site)
• Finish system (product name, number of coats, application method)

Why This Matters

A detailed specification protects the design intent, reduces change orders, and provides a clear standard for quality verification during construction. It also demonstrates to the client that the design team understands the material and its requirements — which builds confidence in the project.