A guide to treated wood selection and use for pole barns and other post-frame buildings.

Pressure-Treated Woodfor Post-Frame Construction

Remember the old adage, “You get what you pay for.” Post-framebuilding design provides exceptional value for your dollar, as it isquick and easy to erect and can provide exceptional long-termenergy efficiency with low maintenance. However, as with anybuilding system, use of sub-standard materials may shorten abuilding’s life-span.

Every building should be properly designed to meet all pertinentcodes and building standards. Codes and recommendationsfrom the manufacturer of products you use may over-riderecommendations within this brochure. Use the best treatedwood products, fasteners, connectors and panels, and your post-frame building will last.

Quality ControlMost wood preserving companies, in order to assure their cus-tomers of properly treated wood, contract with an independentinspection agency, accredited by the American Lumber StandardCommittee, to monitor their production procedures.

These agencies check to see that standards of the AmericanWood Protection Association are being met. This includes,depending on the product, species, and intended use, an appro-priate degree of preservative retention and penetration in sampleborings from each treating operation.

Avoiding CorrosionThe galvanized hardware recommended for use with CCA-treated wood may not be suitable for use with new water-bornpreservatives. Products such as ACQ and CA have a significantlyhigher copper concentration, which conducts electricity and maycause corrosion.

Generally, most component manufacturers recommend you notallow panels or flashing to come into contact with treated wood.Many manufacturers recommend installation of a barrier mate-rial that will stop all electrical current between the treated woodand metal components. Furthermore, do not allow water to drainoff of treated wood onto panels or flashing.

Manufacturers of both the preservatives and the hardware areconsistent in recommending either stainless steel or hot-dippedgalvanized fasteners meeting ASTM A 153 and connectors meet-ing Class G185 sheet of ASTM A 653 – or better – for use withtreated wood. In Permanent Wood Foundations or where saltspray is present, 300 series stainless steel hardware or better isrecommended. Aluminum should not be used in contact withcopper-based treated wood.

Note also that as the retention level of the treated lumber goes up,or depending upon the corrosiveness of the environment in whichthey are being used, fastener and hardware upgrades may be rec-ommended. Most manufacturers recommend a minimum ofHot-Dip Galvanized or Type 304 Stainless Steel be used withtreated wood.

The International Building Code’s Fastener Statement, Section2304.9.5, says: Fasteners for preservative-treated and fire-retar-dant-treated wood shall be of hot-dipped zinc-coated galvanizedsteel, stainless steel, silicon bronze or copper. It further states thatthe coating should be in accordance with ASTM A 153.

The International Residential Code, Section R319.3, says:Fasteners for pressure-preservative treated wood shall be of hot-dipped galvanized steel, stainless steel, silicon bronze or copper.Exception: One-half inch (12.7 mm) diameter or greater bolts.

Post-Frame - A Permanent Building Solution

Panel/Trim Surface Material

Zinc (Galvanized)Aluminum-Zinc Alloy

(e.g. Galvalume)Copper

Stainless SteelAny material at or below ground level

Hot-Dip Galvanized *YesYes

NoNoNo

CopperNoNo

YesNoNo

Stainless SteelYesYes

YesYes

Yes**

Common Fastener Recommendations from Manufacturers for Treated Wood

Fastener Metal

* Fasteners with a zinc coating that meets or exceeds ASTM A 153 Class D thickness specifications.** Stainless Steel 300 series or other stainless steel with equivalent documented corrosion resistance for this application.

For best results, use the same types of metal for fasteners, panels and other components that are in contact with each other.

Pressure-Treated Wood for Post-Frame ConstructionProperly treated wood may last many decades in contact with soil,making post-frame construction a quality building option forlong-term use.

For post-frame construction, pressure-treated wood is primarilyused for skirtboards and building posts or laminated columns.Plywood sheathing, girts and other framing members may also betreated in areas prone to aggressive attack by termites or ifincreased fire resistance is desired.

The most popular preservatives now in use for post-frame con-struction are chromated copper arsenate (CCA), alkaline copperquaternary (ACQ), copper azole (CA), and several less widelyused treatments.

Specifying by UseThe American Wood Protection Association, which establishesthe standards for preservatives and treated wood, now organizesstandards by a Use Category system. Applications for post-framebuilding use are highlighted in the table below.

UseCategory

UC4A

UC4B

UC4C

Description

Exterior, ground orfreshwater contact in areas

with low riskExterior, ground or

freshwater contact, severeenvironments, high potential

for deterioration

Exterior, ground or freshwater contact, verysevere conditions or very

critical structural components

Examples

Fence posts, deck posts, poles, minimum treatment for skirtboards

on post-frame buildings Utility poles, building poles,

permanent wood foundations, minimum treatment for

post-frame building posts and laminated columns

Freshwater piling, foundation piling,utility poles in tropical environments

CCAN/A

.60 (Posts larger

than 5x5" or laminatedcolumns only)

.80(Posts larger

than 5x5" or laminatedcolumns only)

ACQ0.40

.60

.80

Copper Azole.21

.31

.41

Minimum Preservative RetentionLevel* pounds per cubic foot

The table above indicates the minimum retention level recommended for various uses. A higher level of retention may be optionallyused under exceptionally harsh conditions or if additional protection for the wood is desired.

CCA Allowed Usage in Post-Frame Building Construction CCA-treated wood is still allowed in most types of post-frame construction in accordance with 2001 AWPA Treated Wood Commod-ity Standards, which may only be applied to CCA. The table below describes where CCA may be used, according to EPA guidelines.

Commodity Standard/Building Type

Solid sawn posts and commodity lumber (including skirtboards, splash-boards and foundation sill plates) less

than 5" on any side (C16)Solid sawn 5x5" & larger posts (C16, C18 or C24) or nail- or glue-laminated columns (C28)

Plywood and wood shingles (C9)Decking, railing, fence pickets, skirt boards, splash boards,

sill plates etc. (C15)

Typical Post-Frame building use,

including residential,

agricultural, etc.

No*

Yes

YesNo

Structures insome marineenvironments

Yes

Yes

YesNo

Agriculturalfence posts(rounded)

Yes

Yes

YesNo

Residentialdecks,

gazebos, playground

equipment, etc.

No

No

Yes**No

* Arch Wood Protection interprets standard C16 (Wood Used on Farms) to include structural members in any dimension, provided they are installed vertically in strictlyagricultural applications. Osmose and Viance interpret the standard to disallow any members less than 5" on any one side. Be sure to comply with the interpretationof the manufacturer of the chemical your wood treater uses.

** CCA-treated plywood and shingles are not prohibited, but they are not recommended for use on playground equipment. Plywood is permissible at all retentions perAWPA C9 (Plywood). CCA is not allowed for any roof-related applications (such as roof trusses) unless members are larger than 5x5" - with the exception of woodshingles.

Published by:

National Frame Building Associationwww.nfba.org

Note: Recommendations included in this publication come from various product manu-facturers and other sources available to NFBA, and are not based upon independenttesting done by NFBA. Nothing herein shall be construed as a guarantee of performance,or an endorsement or non-endorsement of any particular product or practice.