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
ionPr
eser
vativ
e
Stan
dard
Expo
sure
ALS
CA
gen
cy L
og
oC
A-C
.06
pcf
AB
OV
E G
RO
UN
DB
rand
Nam
e o
rLo
go
AW
PA
U1,
UC
3B
UNDE
RSTA
NDIN
G TH
E END
TAG
FENC
E PIC
KETS
ABOV
E GRO
UND,
PRO
TECT
EDUs
e Cat
egor
y 3B
or h
ighe
r
PORC
H FL
OORI
NGAB
OVE G
ROUN
D, P
ROTE
CTED
Use C
ateg
ory 3
A or
hig
her
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
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