Specifying with AWPA Use Categories for Construction

Guidance for properly specifying and using preserved wood productsPRESERVESPEC

The purpose of the American Wood Protec on Assn. (AWPA) Use Category system is to provide a simple way to select preserved wood products by rela ng the end use of wood product directly to the appropriate AWPA Standard. Use Categories defi ne a series of diff erent exposures for preserved wood products that may be used in construc on.

The advantage of Use Categories is simplicity. The smaller the Use Category number, a lesser amount of protec on is required to protect against decay or insect a ack. Likewise, the largest Use Category number provides the highest degree of protec on. For residen al construc on, preserved wood products are available in Use Categories ranging from UC1 for interior, dry uses to UC4B for ground contact applica ons where the wood is a cri cal component or hard to replace.

For typical construc on uses, refer to Use Categories specifi ed for sawn products under Commodity Specifi ca on A. Review the exposure condi ons defi ned below or the table on the next page to select the proper Use Category. Next, refer to the Specifi ca on Guide table for the specifi c product, preserva ve and reten on (level of preserva ve in the wood) for the respec ve Use Category.

AWPA Use Categories for Typical Construc on Applica ons (Per AWPA Commodity Specifi ca on A)

UC1 – Interior, DryWood used in interior construc on not in contact with the ground or founda ons. Such products are con nuously protected from weather and interior sources of water such as leaking plumbing, condensate, pools and spas.Applica ons - Interior furniture, construc on furnishings, millwork.

UC2 — Interior, DampWood used for interior construc on that are not in contact with ground, but may be subject to dampness. These products are con nuously protected from the weather, but may be exposed to occasional sources of moisture.Applica ons - Interior beams, mbers, fl ooring, framing, millwork, sill plates.

UC3A — Above Ground, ProtectedWood used in exterior construc on that are coated and not in contact with the ground. Such products may be exposed to the full eff ects of weather, but are in ver cal exterior walls or other types of construc on that allows water to quickly drain from the surface.Applica ons - Coated millwork, siding, trim.

UC3B — Above Ground, ExposedWood used in exterior construc on and not in contact with the ground. Materials do not require an exterior coa ng, but may be fi nished to achieve a desired aesthe c appearance. For Commodity Spec. A: See Note 1 under UC4A for sawn components that may be physically above ground but that are required to be treated for ground contact. This includes sawn components that are diffi cult to replace and cri cal to the structure, or that may be exposed to ground contact type hazards due to climate, ar fi cial or natural processes or construc on. Applica ons - Decking, railings, joists and beams for decks and freshwater docks, fence pickets, uncoated millwork.

Western Wood Preservers Institute ■ 12503 SE Mill Plain Blvd., Suite 205 ■ Vancouver, WA 98684 Western Wood Preservers Institute provides this information from sources believed to be true. However, neither WWPI or its members

guarantee the accuracy of any information published herein and these parties are not responsible for any errors, omissions or damages arising out of or relating to its use. This document is published with the understanding that WWPI, its members and

the authors are supplying information, but are not attempting to render engineering or other professional services.PS001-0520

UC4A — Ground Contact, General UseWood used in (1) contact with the ground, fresh water, or other situa ons favorable to deteriora on; (2) used above ground but are diffi cult to maintain, repair or replace and are cri cal to the performance and safety of the en re system/construc on; or (3) used above ground but may end up in ground contact or are subject to hazards comparable to ground contact due to climate, ar fi cial or natural processes or construc on.Note 1: The following sawn components for exterior above ground use shall be treated to Ground Contact UC4A or higher requirements: a) When there is a reasonable expecta on that soil, vegeta on, leaf li er or other debris may build up and remain in contact with the component. b) When the construc on itself, other structures or an cipated vegeta on growth will not allow air to circulate underneath the construc on and between decking boards. c) When components are installed less than 6 inches above ground (fi nal grade a er landscaping) and supported on permeable building materials (e.g. treated wood or concrete). d) When components are in direct contact with non-durable untreated wood, or any older construc on with any evidence of decay. e). When components are we ed on a frequent or recurrent basis (e.g., on a freshwater fl oa ng dock or by a watering system). f) When components are used in tropical climates.Applica ons - Fence posts, deck posts, structural lumber, joists and beams for decks and freshwater docks, mbers.

UC4B – Ground Contact, Heavy DutyWood used in contact with the ground either in severe environments, such as hor cultural sites, in climates with a high poten al for deterio-ra on or in cri cally important components.Typical Applica ons - Permanent wood founda ons, building poles.

i n s t i t u t e

W E S T E R NWOOD PRESERVERS

Est. 1947

Service Condi ons for Use Categories Use

Category Service Condi ons Use EnvironmentCommon Agentsof Deteriora on Typical Applica ons

UC1Interior, Dry

Interior construc onAbove Ground, Dry

Con nuously protected from weather or other sources of

moisture

Insects only Interior construc on and furnishings

UC2Interior, Damp

Interior construc on Above Ground, Damp

Protected from weather, but may be subject to sources of

moisture

Decay fungi and insects Interior construc on, sill plates

UC3AAbove Ground,

Protected

Exterior construc on Above Ground

Coated & rapid water runoff

Exposed to all weather cycles, including intermi ent we ng

Decay fungi and insects Coated millwork, siding, trim

UC3BAbove Ground,

Exposed(Commodity

Specifi ca on A only)

Exterior construc onAbove Ground

Uncoated or poor water run-off .Excludes above ground

applica ons with ground contact type hazards.

Exposed to all weather cycles including intermi ent we ng

but with suffi cient air circula on so wood can readily dry

Decay fungi and insects Decking, railings, joists and beams for decks and

freshwater docks1, fence pickets, uncoated millwork

UC4AGround Contact,

General Use(Commodity

Specifi ca on A only)

Ground Contact or Fresh WaterNon-cri cal components(Includes above ground

applica ons with ground contact type hazards or that are

cri cal or hard to replace)

Exposed to all weather cycles, including prolonged we ng

Decay fungi and insects Sawn fence, deck and guardrail posts, joists and beams for

decks and freshwater docks1

UC4BGround Contact,

Heavy Duty

Ground Contact or Fresh WaterCri cal components ordiffi cult replacement

Exposed to all weather cycles, including con nuous or

prolonged we ng, high decay poten al includes salt water

splash

Decay fungi and insects with increased poten al

for biodeteriora on

Permanent wood founda ons, sawn hor cultural posts

Source: AWPA 2020 Book of Standards, Table 2-11 Joists and beams shall be treated to requirements for UC4A when they are diffi cult to maintain, repair or replace and are cri cal to the performance and safety of the en re system/construc on.

Waterborne Preserva ves for Construc on Products

ACQ - Alkaline Copper Quaternary Brands: Preserve® ACQ, NatureWood® Species: Douglas Fir, Hem-FirUse: Above ground, ground contact, fresh water contact, salt water splashAvailability: Home centers, lumber yards, distributors

Consumers today have a variety of preserved wood products to choose from that off er the durability and performance needed for any applica on. The preserva ves available today contain components that are approved by the EPA and provide an eff ec ve way to preserve the natural benefi ts of wood.

Western preserved wood products are commonly available pressure-treated with the following waterborne preserva ves:

CA - Copper Azole Brands: Wolmanized® Outdoor® Wood, Preserve® CA, NatureWood® CASpecies: Douglas Fir, Hem-FirUse: Above ground, ground contact, fresh water contact, salt water splashAvailability: Home centers, lumber yards, distributors

EL2 - DCOI-Imidacloprid Brand: Ecolife™, Severe Weather® MAX Species: Douglas FirUse: Above ground onlyAvailability: Home centers, lumber yards, distributors

PTI - Propiconazole-Tebuconazole-Imidacloprid Brands: Wolmanized® EraWood®, Nexwood® Species: Douglas Fir, Hem-FirUse: Above ground onlyAvailability: Home centers, lumber yards, distributors

SBX - Inorganic Boron Brands: PacBor®, TimBor®, HiBor®, SilBor®, AdvanceGuard®, TimberSaver®, Cellu-Treat®Species: Douglas Fir, Hem-Fir, Southern Yellow PineUse: Interior applica ons; “where its applica on is con nually protected from liquid water.” Availability: Home centers, lumber yards, distributors

Specifying with Use Categories for Construction Page 2

Specifying with Use Categories for Construction Page 3

Use Category ACQ CA-C EL2 PTI SBX/DOTDECKS, OUTDOOR LIVINGDecks, Residen al Decking boards 3B 0.15 0.06 0.019 0.018 (2) NL Joists and beams, above ground (1) 3B or 4A 0.15 or 0.40 0.06 or 0.15 0.019 or NL 0.018 (2) or NL NL Joists and beams, ground contact 4A 0.40 0.15 NL NL NL Ledger board 4A 0.40 0.15 NL NL NL Posts, structural 4A 0.40 0.15 NL NL NL Railing 3B 0.15 0.06 0.019 0.018 (2) NL Stairs (1) 3B or 4A 0.15 or 0.40 0.06 or 0.15 0.019 or NL 0.018 (2) or NL NLGarden box 4A 0.40 0.15 NL NL NLLandscape wall 4A 0.40 0.15 NL NL NLPorch fl ooring, covered 3B 0.15 0.06 0.019 0.018 (2) NL

BUILDING CONSTRUCTION MATERIALFascia, trim 3A 0.15 0.06 0.019 0.013 NLFraming lumber, studs - interior 1 or 2 0.15 0.06 0.019 0.013 0.25 (6)

Permanent Wood Founda on Lumber (3) 4B 0.60 0.31 NL NL NL Plywood (3) 4B 0.60 0.31 NL NL NLPlywood Sub-fl oor, damp, above ground 2 0.15 0.06 0.019 0.013 0.25 (6)

Exterior, above ground 3B 0.15 0.06 0.019 0.018 (2) NL Ground contact 4A 0.40 0.15 NL NL NL Out of contact with ground and con nuously protected from liquid water

2 0.15 0.06 0.019 0.013 0.25 (6)

Poles, building Round 4A or 4B 0.60 0.31(4) NL NL NL Sawn 3B 0.15 0.06 NL NL NLSill plate 2 0.15 0.06 0.019 0.013 0.25 (6) Shakes and shingles (3) 3B 0.15 0.06 NL NL NL

FENCINGPickets, slats, trim 3A or 3B 0.15 0.06 0.019 0.018 (2) NLPosts, sawn 4A 0.40 0.15 NL NL NLPosts, round 4A 0.40 0.15 (5) NL NL NLRail 3A or 3B 0.15 0.06 0.019 0.018 (2) NL

Specifi ca on Guide for Preserved Wood in Construc on Applica ons

Source: AWPA 2020 Book of Standards, Table 3-1 and U-1, Commodity Specifi ca on A

NL - Not Listed in the AWPA StandardsReten ons listed in pcf, or pounds per cubic foot

(1) See applica on recommenda ons for Use Categories 3B and 4A(2) For certain species, use of an accepted water repellent addi ve allows 0.013 pcf

(3) PWF components, shakes and shingles can be treated with CCA at 0.60 pcf(4) Western Red Cedar only(5) Lodgepole Pine only(6) Equivalent to 0.17 pcf B2O3

Footnotes

Use C

ateg

ory (

UC) i

nfor

matio

n is f

ound

on th

e end

tag o

r tre

atme

nt st

amp

Grou

nd C

onta

ct, f

resh

wat

erUC

4A –

Gen

eral

use 1

UC4B

– H

eavy

duty

UC4

Abov

e Gro

und,

exte

rior c

onstr

uctio

nUC

3A -

Coat

ed, r

apid

wate

r run

off

UC3B

- Un

coat

ed, p

oor w

ater

runo

ff 1

UC3

Inter

ior C

onstr

uctio

n, ab

ove g

roun

d, da

mp

UC2

Abov

e Gro

und c

ompo

nent

s tha

t may

be re

quire

d to b

e pre

serve

d for

grou

nd co

ntac

t inc

lude j

oists

and b

eams

th

at ar

e diff

icult

to re

place

and c

ritica

l to t

he st

ructu

re or

comp

onen

ts th

at ma

y be e

xpos

ed to

grou

nd co

ntac

t typ

e haz

ards

due t

o clim

ate, a

rtific

ial or

natu

ral p

roce

sses

or co

nstru

ction

.

NOTE

: This

is de

signe

d to h

elp id

entif

y the

appr

opria

te Us

e Cate

gory

for th

e int

ende

d use

. Som

e com

modit

ies

may r

equir

e a re

tentio

n for

a sp

ecific

appli

catio

n bey

ond t

hat s

ugge

sted,

due t

o the

criti

cal n

ature

of th

eir us

e. Th

e des

igner

shou

ld us

e the

ir be

st jud

geme

nt to

deter

mine

the a

ppro

priat

e spe

cifica

tion f

or a

parti

cular

use.

1

–SE

LECT

THE

RIG

HT P

RESE

RVED

WOO

D FO

R YO

UR P

ROJE

CT–

AMER

ICAN

WOO

D PR

OTEC

TION

ASS

OCIA

TION

(AW

PA) P

RESE

RVED

WOO

D US

E CA

TEGO

RIES

Co

mp

any

Nam

e, C

ity,

Sta

teRe

tent

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vativ

e

Stan

dard

Expo

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ALS

CA

gen

cy L

og

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pcf

AB

OV

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RO

UN

DB

rand

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go

AW

PA

U1,

UC

3B

UNDE

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FENC

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ABOV

E GRO

UND,

PRO

TECT

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e Cat

egor

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or h

ighe

r

PORC

H FL

OORI

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OVE G

ROUN

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CTED

Use C

ateg

ory 3

A or

hig

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SIDI

NG,

FASC

IA &

TRIM

ABOV

E GRO

UND,

PRO

TECT

EDUs

e Cat

egor

y 3A

or h

ighe

rDE

CK R

AILIN

GAB

OVE G

ROUN

D 1

Use C

ateg

ory 3

B or

hig

her

LAND

SCAP

E WAL

LGR

OUND

CON

TACT

Use C

ateg

ory 4

A or

hig

her

POST

SGR

OUND

CON

TACT

Use C

ateg

ory 4

A or

hig

her

PLAN

TER

BOX

GROU

ND C

ONTA

CTUs

e Cat

egor

y 4A

or h

ighe

r

PERM

ANEN

T WOO

D FO

UNDA

TION

GROU

ND C

ONTA

CTUs

e Cat

egor

y 4B

or h

ighe

r

SILL

PLA

TEAB

OVE G

ROUN

DUs

e Cat

egor

y 2 o

r hig

her

DECK

BOA

RDS

ABOV

E GRO

UND

1

Use C

ateg

ory 3

B or

hig

her

STRU

CTUR

AL

POST

SGR

OUND

CON

TACT

Use C

ateg

ory 4

A or

hig

her

LEDG

ERGR

OUND

CON

TACT

1

Use C

ateg

ory 4

A or

hig

her

SHAK

ES &

SHI

NGLE

SAB

OVE G

ROUN

DUs

e Cat

egor

y 3B

or h

ighe

r

JOIS

TS &

BEA

MSAB

OVE G

ROUN

D 1

Use C

ateg

ory 3

B or

hig

her

GROU

ND C

ONTA

CTUs

e Cat

egor

y 4A

or h

ighe

r

STAI

RSAB

OVE G

ROUN

D 1

Use C

ateg

ory 3

B or

hig

her

GROU

ND C

ONTA

CTUs

e Cat

egor

y 4A

or h

ighe

r