Standards
Classification, not prediction
Exposure, use and durability classes
Four published scales, each as its own standard defines it, and one thing done with them: compare what you have selected against the exposure it will live in, and say which class sits below the other. The order is the standard’s, not this site’s.
There are no figures in years anywhere on this page. Predicting a service life is a discipline with its own standard — ISO 15686 — and it needs exposure data, product performance data and a probabilistic model. This site holds none of the three, so it classifies and compares, and leaves the specification to the person doing the work and the standard that gives the method.
ISO 9223, and the same categories as used by ISO 12944-2
Classifies how corrosive an atmosphere is to metal · published by International Organization for Standardization.
| Class | What it describes |
|---|---|
| C1 | Very low. Heated buildings with clean atmospheres. |
| C2 | Low. Unheated buildings where condensation occurs, and rural atmospheres with low pollution. |
| C3 | Medium. Urban and industrial atmospheres with moderate sulfur dioxide, and coastal areas with low salinity. |
| C4 | High. Industrial areas, and coastal areas with moderate salinity. |
| C5 | Very high. Industrial areas with high humidity and an aggressive atmosphere, and coastal areas with high salinity. |
| CX | Extreme. Offshore areas with high salinity, and industrial areas with extreme humidity and an aggressive atmosphere. |
A corrosivity category describes an ATMOSPHERE, not a product. It does not say how long a coating or a fastener will last, and no figure in years follows from it.
The exposure you described is CX — Extreme. Offshore areas with high salinity, and industrial areas with extreme humidity and an aggressive atmosphere. What you have selected is classed C1 — Very low. Heated buildings with clean atmospheres. C1 is below CX on ISO 9223.
For protective paint systems, ISO 12944-5 gives systems by corrosivity category and by the durability range required. For stainless steels in construction, EN 1993-1-4 Annex A gives a selection method using corrosion resistance classes. Both are selection decisions made by the person specifying the work.
EN 335, Durability of wood and wood-based products — Use classes
Classifies how wet a piece of timber's service situation is · published by European Committee for Standardization, as published in the UK by BSI.
| Class | What it describes |
|---|---|
| UC1 | Interior, dry, covered. No wetting. |
| UC2 | Interior or covered, with a risk of wetting — condensation, or occasional damp. |
| UC3.1 | Above ground, exposed to weather, where water does not accumulate. |
| UC3.2 | Above ground, exposed to weather, where water does accumulate. |
| UC4 | In contact with ground or fresh water. |
| UC5 | In salt water. |
A use class describes where the timber is, not what it is. It says nothing about how long a species or a treatment lasts there, and it is not a specification of a preservative or a retention.
The exposure you described is UC5 — In salt water. What you have selected is classed UC1 — Interior, dry, covered. No wetting. UC1 is below UC5 on EN 335.
What treatment a use class calls for is the treatment standard's and the treater's answer — in Europe, EN 599-1 for preservative performance and the treater's own specification for retention and penetration.
EN 350, Durability of wood and wood-based products
Classifies how durable a timber species is against wood-destroying fungi, untreated · published by European Committee for Standardization, as published in the UK by BSI.
| Class | What it describes |
|---|---|
| DC1 | Very durable heartwood. |
| DC2 | Durable heartwood. |
| DC3 | Moderately durable heartwood. |
| DC4 | Slightly durable heartwood. |
| DC5 | Not durable heartwood. |
EN 350 classifies the HEARTWOOD of a species. The sapwood of nearly every species is not durable, whatever the heartwood's class — which is the most common misreading of a durability class, and the reason it is written here.
The exposure you described is DC5 — Not durable heartwood. What you have selected is classed DC1 — Very durable heartwood. DC1 is below DC5 on EN 350.
Whether a species' natural durability is enough for a situation is read against the use class that situation sits in (EN 335), and where it is not enough the timber is treated. Neither decision is made here.
AWPA U1, the Use Category System
Classifies what a piece of treated wood is exposed to, in the United States · published by American Wood Protection Association.
| Class | What it describes |
|---|---|
| UC1 | Interior, dry. |
| UC2 | Interior, damp. |
| UC3A | Exterior, above ground, coated, with water running off. |
| UC3B | Exterior, above ground, uncoated or poorly drained. |
| UC4A | Ground contact, general use. |
| UC4B | Ground contact, heavy duty. |
| UC4C | Ground contact, extreme duty. |
| UC5A | Marine use, northern waters. |
| UC5B | Marine use, central waters. |
| UC5C | Marine use, southern waters. |
A use category says what the exposure is. The retention and the preservative that go with it are in the commodity specifications of the same standard, and on the tag stapled to the timber — not here.
The exposure you described is UC5C — Marine use, southern waters. What you have selected is classed UC1 — Interior, dry. UC1 is below UC5C on AWPA U1.
AWPA U1's own commodity specifications give the preservative and retention for each use category, and the treated wood's end tag states what it was treated to. That tag is the authority on the piece in your hands.
Every standard named here is listed with the rest of the site’s citations on the standards index. No text of any standard is reproduced on this site, and no adoption is claimed.