Borate-Treated Lumber and Plywood in Miami: Where It Fits and Where It Fails

Borate-treated plywood and lumber in Miami is a good fit for framing and sheathing that stays inside the building, dry or only occasionally damp, and a poor fit for anything exposed to rain, soil or standing water. This guide explains what borate treatment does, where it belongs, where it fails, how it differs from copper-based pressure-treated wood and fire-retardant plywood, and what to tell us when you order.

What Borate-Treated Wood Is

The WoodWorks termite-protection paper says pressure-preservative-treated wood is typically treated with borate or copper-based preservatives, and that both protect wood from termites and decay. Pressure treatment drives the preservative into the wood, which is different from a surface spray or brush coat. Borate is a water-soluble preservative, and that single property decides almost everything about where it can be used.

The AWPA U1 standard excerpt lists inorganic boron (SBX) among the preservatives in the standard. For the exposure rules below we rely on the WoodWorks and Preserved Wood documents, because the AWPA excerpt we reviewed defines the use categories but does not say which preservatives suit each one.

Where Borate Fits

The Preserved Wood use-category guide describes the two interior use categories this way: UC1 is above-ground interior construction that is dry, protected from weather and from interior water sources such as leaking plumbing, condensate, pools and spas; UC2 is above-ground interior construction that is damp. It adds that the chief threat in those categories is termites, so they are typically preserved with borates. Typical products it lists include studs, joists, roof trusses, furniture and millwork, and sill plates in interior construction.

• Good candidates: interior wall framing, interior sheathing and plywood that will be enclosed, trusses and joists inside the building envelope, and millwork substrates that stay dry.
• The test: will the piece be enclosed and protected from liquid water for its whole life? If yes, borate is a candidate. If there is any doubt, ask the designer or the building official before you order.

Where Borate Fails

WoodWorks states that borate can lose its effectiveness when exposed to liquid moisture, and that AWPA standards allow borate-treated wood to be used only in interior applications that are dry or exposed to occasional dampness. Copper-based treatments are not water soluble and are used where wood will be exposed to the elements.

• Do not use borate for: ground contact, fence posts, exterior decks, pergolas, landscape timbers, or any piece left to weather during construction.
• Use instead: copper-based pressure-treated lumber rated for the exposure. See our pressure-treated lumber page and our guide to pressure-treated lumber in South Florida humidity.

Why Miami Buyers Ask About It

The UF/IFAS Formosan subterranean termite publication says the Formosan subterranean termite is distributed throughout Florida, primarily in urban areas with high population density, and that its underground colonies can reach several million individuals. UF/IFAS describes the species as a major structural pest and says that, because of their large population size and foraging distance, a Formosan colony can cause significant structural damage.

That is why specifications for South Florida buildings sometimes call for a higher borate level. WoodWorks says AWPA standards define two levels of borate treatment: a lower loading for native subterranean termites and a higher loading for areas where Formosan termites may be present. Preserved Wood says the same in a sentence: for areas where the Formosan termite is present, higher borate retentions are specified. We do not quote retention numbers in this guide because the right figure comes from your plans, your engineer or the treater’s documentation. Whether borate treatment satisfies a specific code or termite-protection requirement on your project is a question for your designer and the building official.

Borate vs Copper-Based Pressure-Treated Wood

Question	Borate-treated	Copper-based pressure-treated
Water solubility (WoodWorks)	Water soluble	Not water soluble
Where it is used (WoodWorks)	Interior, dry or occasionally damp	Where wood is exposed to the elements
Ground contact or weather	No	Yes, when rated for that exposure
During construction	Keep wrapped and dry until enclosed	Follow the product’s exposure rating
Field cuts and holes (WoodWorks, AWPA M4)	Treat with a borate-containing field treatment	Treat with copper naphthenate or oxine copper for exterior use
How we supply it	Special order	See our pressure-treated lumber page

Figures and rules in this table are statements from the sources linked in this article, not International Plywood & Lumber specifications.

Specifying It Correctly

A borate order is easier to fill, and easier to inspect, when the specification is complete. Before you send it to us, confirm these from your plans or your engineer:

1. The use category the piece will live in (interior dry or interior damp)
2. The borate level required, native subterranean or Formosan, as your documents define it
3. Species, grade, thickness and sheet or board sizes
4. Whether the piece is framing, sheathing, plywood or millwork stock
5. The treatment documentation your inspector will expect from the treater

Handling and Site Rules

Because borate is water soluble, treat the material like a finished interior product. Keep it wrapped and dry from delivery until the building is enclosed, and do not leave it exposed to rain. WoodWorks says that when treated wood is cut or drilled on site, building codes require surface treatment on the cut ends and holes, and that interior applications use a borate-containing field treatment under AWPA Standard M4. It also notes that treated wood in interior locations must be protected with two coats of urethane, shellac, latex epoxy or varnish unless waterborne preservatives are used, so check the treater’s finishing instructions before you coat anything.

Common Mix-Ups

• Borate is not fire-retardant treatment. They are different chemistries for different problems. If your plans call for a flame-spread rating, see our fire-retardant plywood page and our guide on when to use fire-retardant plywood.
• Borate is not ground-contact treated wood. If the piece touches soil or concrete in a wet location, you need a copper-based product rated for it.
• Borate is not a substitute for a termite plan. It is one protection method. Your project’s termite protection requirements come from your designer and the local building official.

Ordering Borate-Treated Lumber and Plywood from International Plywood & Lumber

International Plywood & Lumber is a plywood and lumber wholesaler serving trade customers in South Florida, serving Miami-Dade, Broward, and Palm Beach counties, with delivery available. We supply borate-treated lumber and plywood by special order. Call (305) 884-0860 and we will confirm pricing and lead time before you commit. To speed up the quote, send:

1. Lumber or plywood, with species, grade, thickness and sizes
2. Quantities
3. The use category or borate level your plans or engineer require
4. Your needed-by date
5. Delivery ZIP code

Buyers in Broward and Fort Lauderdale can also see our Broward County plywood delivery page and our Fort Lauderdale plywood and lumber page. Request a trade quote on our contact page or call (305) 884-0860. Hablamos Español.

Frequently Asked Questions

Is borate-treated lumber safe to use outdoors?

No, not for exposed outdoor use. WoodWorks says borate is water soluble and can lose its effectiveness when exposed to liquid moisture, and that AWPA standards allow borate-treated wood only in interior applications that are dry or exposed to occasional dampness. For exterior or ground-contact work, use copper-based pressure-treated lumber rated for that exposure.

What is the difference between borate-treated and regular pressure-treated lumber?

The preservative. According to WoodWorks, pressure-treated wood is typically treated with borate or copper-based preservatives. Borate is water soluble and belongs indoors. Copper-based treatments are not water soluble and are used where wood is exposed to the elements.

Does borate treatment protect against Formosan termites?

Preserved Wood says higher borate retentions are specified for areas where the Formosan termite is present, and WoodWorks says AWPA defines a higher loading for those areas. Confirm the required level on your plans and with your engineer, and treat borate as one part of the project’s termite protection, not a guarantee.

Is borate-treated plywood the same as fire-retardant plywood?

No. Borate treatment addresses termites and decay in interior applications. Fire-retardant plywood is a separate product made to a different performance requirement. If your plans call for a flame-spread rating, see our fire-retardant plywood page.

Can I paint or seal borate-treated wood?

Often yes, but follow the treater’s instructions. WoodWorks notes that treated wood in interior locations must be protected with two coats of urethane, shellac, latex epoxy or varnish unless waterborne preservatives are used. Cut ends and drilled holes need a borate-containing field treatment under AWPA M4.

Does International Plywood & Lumber carry borate-treated lumber and plywood?

We supply borate-treated lumber and plywood by special order. Call (305) 884-0860 with your species, sizes, quantities and needed-by date, and we will confirm pricing and lead time before you commit.