EHCI Learning & Certification
Exterior hardwood glossary
Plain-language definitions of the terms used across EHCI courses, assessments, specifications and supplier documentation.
A
- Acclimation
- Allowing lumber to reach moisture equilibrium with the installation environment before fixing, typically stored flat, stickered and under cover.
- Air-dried (AD)
- Lumber dried by natural air circulation; moisture content is higher and less uniform than kiln-dried stock.
B
- Back-priming
- Sealing the concealed face and ends of cladding or trim to slow moisture uptake and reduce cupping.
- Blind fastening
- Fixing boards with hidden clips or angled screws so no fastener heads show on the walking or facing surface.
C
- Checking
- Small surface or end cracks along the grain caused by uneven drying stresses.
- CITES
- Convention on International Trade in Endangered Species; certain hardwoods require export permits and chain-of-custody documentation.
- Cupping
- Board distortion where the edges rise or fall relative to the center, driven by moisture differences between faces.
D
- Durability class
- A rating of natural resistance to decay fungi and insects, from very durable to perishable, based on standardized field or lab tests.
E
- Equilibrium moisture content (EMC)
- The moisture content wood eventually reaches at a given temperature and relative humidity.
- End sealing
- Applying wax or sealer to freshly cut board ends to slow moisture exchange and reduce end checking.
- Extractives
- Natural chemical compounds in heartwood that contribute to color, durability and, in some species, finish or corrosion issues.
F
- Fastener corrosion
- Degradation of metal fixings by moisture, tannins or salt; mitigated by stainless steel grades appropriate to exposure.
- Fiber saturation point
- The moisture content (roughly 25–30%) below which wood begins to shrink as it dries.
- FSC / PEFC
- Third-party forest management certification schemes providing chain-of-custody assurance.
G
- Gapping
- The spacing left between deck or cladding boards for drainage, ventilation and movement.
H
- Heartwood
- The inner, non-living wood of a tree, generally darker and more decay-resistant than sapwood.
I
- Interlocked grain
- Grain that alternates direction between growth layers, increasing tearout risk when machining.
J
- Janka hardness
- Force required to embed a steel ball halfway into wood; a proxy for wear and dent resistance.
- Joist ventilation
- Air movement beneath a deck that allows both board faces to dry at similar rates.
K
- Kiln-dried (KD)
- Lumber dried under controlled heat and humidity to a target moisture content.
L
- Ledger
- The structural member attached to a building that supports deck joists; flashing and fastening are critical.
M
- Moisture content (MC)
- Water weight in wood expressed as a percentage of oven-dry weight.
- Movement coefficient
- The dimensional change per unit change in moisture content, differing between tangential and radial directions.
P
- Penetrating oil finish
- A finish absorbed into the wood surface rather than forming a film, favored for dense hardwoods.
- Pre-drilling
- Boring pilot holes before driving fasteners to prevent splitting and fastener failure in dense species.
Q
- Quartersawn
- Boards cut with growth rings roughly perpendicular to the face, giving greater stability.
R
- Rain-screen
- A cladding assembly with a ventilated cavity behind the boards that allows drainage and drying.
S
- Sapwood
- The outer, living wood of a tree; lighter, less durable and usually excluded from exterior grades.
- Silica content
- Mineral deposits in some tropical species that rapidly dull cutting tools.
- Span table
- Published maximum distances between supports for a given species, thickness and load.
- Stainless steel 304 / 316
- Corrosion-resistant fastener alloys; 316 is specified for coastal and marine exposure.
- Stickering
- Placing spacers between stacked boards so air can circulate during acclimation.
T
- Tannin bleed
- Dark staining from water-soluble extractives, often around fasteners or on surfaces below.
- Tearout
- Fibers torn from the surface during planing or routing, common with interlocked grain.
U
- UV degradation
- Surface graying and fiber breakdown caused by sunlight, slowed by pigmented finishes.
W
- Weathering
- Natural color change and surface erosion from sun, rain and temperature cycling.