If you’ve spent any time around deck builders, lumberyards, or treated wood suppliers, you’ve probably seen the acronym KDAT. You may have also seen it on job sites, in spec sheets, or stamped right on the lumber itself. But what is KDAT lumber, exactly — and why does it matter so much for the decks you’re building?

This guide covers everything: what KDAT means, how it’s made, why it performs better than standard pressure treated lumber, what it costs, and what to realistically expect when you spec it for your next build.

What Does KDAT Stand For?

KDAT stands for Kiln Dried After Treatment. It refers to pressure treated lumber that goes through an extra drying step in an industrial kiln after the chemical treatment process is complete.

To understand why that extra step matters, you need to understand what happens during standard pressure treatment.

The pressure treating process

When lumber is pressure treated, it’s loaded into a large cylinder and saturated with a chemical preservative — typically Micronized Copper Azole (MCA) — under high pressure. The chemicals bond to the wood fiber and protect it from rot, decay, and insects for decades.

The problem: that process also floods the wood with water. A standard “wet” or “green” pressure treated board can have moisture content well above 50% when it leaves the treating plant. Wood at that moisture level will shrink, cup, warp, and twist as it slowly dries out over the next 8 to 12 months — and that movement happens after it’s already been built into your deck.

What the kiln does

KDAT lumber goes back into an industrial kiln after treatment. Using controlled temperatures and even airflow between every board, the kiln removes up to 80% of the moisture introduced by the treating process. The result is a much drier, more dimensionally stable piece of lumber — typically targeting 12–19% moisture content at the time it leaves the facility.

That’s the core difference. Same chemical protection. Same treatment grades. Just a dramatically drier, more stable board.

KDAT Lumber Benefits: What You Actually Get on the Job Site

Six reasons deck builders specify KDAT:

• Stain, paint, or seal immediately — no waiting 8 to 12 months for the wood to dry
• Minimized warp, cup, twist, and check — most of the moisture movement has already happened
• Lighter weight — easier to handle, cut, and install on the job site
• Better nail and screw holding power than wet lumber
• Increased deck frame stability — joists don’t move after installation
• Fewer callbacks — the deck you build today stays flat

Each of these benefits traces back to one thing: the wood is already dry when you install it. With green or wet lumber, the drying happens on your deck. With KDAT, it happened in the kiln.

KDAT vs Green Treated Lumber: The Numbers Side by Side

Here’s how KDAT compares to standard green or wet pressure treated lumber on the factors that matter most to deck builders:

Why This Matters for Composite Decks Especially

KDAT’s performance advantage is most visible when it’s used as the substructure under composite decking — Trex, TimberTech, Fiberon, and similar products.

Composite deck boards are designed to be dimensionally stable. They don’t shrink. They don’t warp on their own. But they are attached to a framing system — and if that framing system is made from green or wet lumber that’s still drying out, the joists will move. As the joists shrink and warp over time, they pull and distort the composite boards sitting on top of them. The result looks like a composite problem. It isn’t. It’s a framing problem.

Builders who switch to KDAT for their composite deck frames report dramatically fewer callbacks related to deck movement and board distortion. The composite performs exactly as it was designed to — because the framing under it is stable from day one.

“As someone who’s been involved with deck building for 30 years, I’m definitely a fan of Northern Crossarm’s KDAT. If you take an ordinary piece of lumber that’s been treated, it will still be wet when you use it. Over time, that board will naturally shrink, which can be a big problem when you’re creating a deck frame. As the framing shrinks, it can warp and distort the composite or wood decking resting on it — which can lead to deck failure. By using KDAT lumber for our deck frames, we receive fewer callbacks, and that’s good for business.”

— Bob Heidenreich, The Deck & Door Store, Apple Valley, MN · 30 years in deck building

What Are the Best Applications for KDAT Lumber?

KDAT is extremely versatile. Because its stability advantage applies anywhere that wood movement causes problems, it’s used across a wide range of applications:

• Deck boards, joists, beams, and stringers
• Deck rails and rail components (2×4, 2×6, 4×4, 6×6, 2×2)
• Pergolas and outdoor shade structures
• Fencing and fence posts
• Bridges and boardwalks
• Sound walls and retaining structures
• Marine construction
• Flatbed trailers
• Storage sheds and backyard structures

For residential and commercial deck building, KDAT’s primary application is deck substructure framing — the joists, beams, rim boards, and posts that everything else sits on.

What Species Is KDAT Lumber Made From?

The most common species used for KDAT deck framing in the eastern United States is Southern Yellow Pine (SYP). SYP is strong, stiff, and has a high proportion of sapwood — which makes it ideal for absorbing the chemical preservative deeply and evenly during the treatment process.

KDAT lumber is available in standard dimensional sizes: 2×4, 2×6, 2×8, 2×10, 2×12 for framing and rail components, and 5/4×6 and 2×6 for decking boards. Posts and beams are available in 4×4, 6×6, and larger sizes depending on structural requirements.

What Does KDAT Lumber Cost?

KDAT treated wood typically runs 15–25% more than standard green or wet pressure treated lumber. That premium reflects the additional kiln drying step, the extra quality control sorting, and the improved performance you get on the job.

Compared to cedar decking, KDAT usually sits in the middle — more affordable than cedar (which runs 30%+ over commodity treated lumber), but significantly more stable and, in many cases, available pre-finished so you skip the staining cost entirely.

Compared to composite decking, KDAT framing costs 50% or more less. When you factor in reduced callbacks, fewer trips back to the job site, and the ability to stain immediately, most builders find the price difference more than pays for itself.

What to Realistically Expect With KDAT Lumber

KDAT is better than green treated lumber — but it’s still wood. There are a few things it will not do:

• Strict dimensional uniformity: Sawn lumber varies in size due to mill inconsistencies. KDAT restores boards close to their original dimensions, but it is not an exact science.
• Exact moisture content: The target is 12–19%, but individual boards will vary. Exposure to moisture after drying will cause moisture content to rise.
• Complete elimination of natural wood characteristics: Some warp, cup, check, and swell can still occur, especially if boards are exposed to wet conditions before installation.

Proper job site handling matters. Store KDAT lumber off the ground, keep it covered until installation, and allow 1/4″ to 3/8″ spacing between deck boards to accommodate any expansion.

Northern Crossarm KDAT: What Sets Our Product Apart

Northern Crossarm Company has been producing treated wood from Chippewa Falls, Wisconsin since 1922. As a third-generation, family-owned operation, we’re one of the largest KDAT treaters in Wisconsin and one of the top KDAT suppliers in the country — with distribution east of the Rocky Mountains through Boise Cascade, Snavely, and an expanding network of stocking dealers including Master Halco’s 80+ locations.

What separates Northern Crossarm KDAT from others on the market:

• Multiple human sort passes after kiln drying — if a board looks questionable, it doesn’t ship. Our cull rate runs 2–3% or less.
• Third-party testing to ensure treatment and drying standards are met consistently.
• Pre-finished KDAT Brown — our Revere product line comes with a rich brown finish applied at the plant, eliminating the need for staining for up to four years.
• KDAT Grey — Northern Crossarm is the only supplier offering a pre-finished grey KDAT, giving builders and homeowners a clean, modern framing aesthetic under any composite product.

“When I toured the Northern Crossarm plant, I was absolutely blown away by the quality control. If a board even looked questionable, it does not make the cut. We could not be more excited about their KDAT product line.”

— Bryan Bolz, ABC Supply Co. Inc., Jackson, WI

Frequently Asked Questions About KDAT Lumber

Is KDAT lumber the same as pressure treated lumber?

Yes and no. KDAT lumber is pressure treated — it goes through the same chemical treatment process. The difference is that it’s kiln dried after that treatment, which removes most of the moisture added during the process. Standard “green” or “wet” pressure treated lumber skips that drying step.

Can I stain KDAT lumber right away?

Yes. Because the kiln drying removes excess moisture, KDAT lumber can be painted, stained, or sealed immediately after installation. With standard wet treated lumber, you typically need to wait 8 to 12 months for the wood to dry before finishes will bond properly.

Does KDAT lumber still protect against rot and decay?

Absolutely. KDAT lumber is pressure treated with chemical preservatives before the kiln drying step. It carries the same treatment retention and use category ratings as standard pressure treated lumber — including AG (above ground), GC (ground contact), and fresh water immersion ratings.

How do I find KDAT lumber near me?

Northern Crossarm distributes KDAT lumber to independent lumberyards and building supply stores east of the Rocky Mountains. Contact us at 715-723-4100 or sales@crossarm.com and we’ll connect you with a stocking dealer in your area.

What if my lumberyard doesn’t stock KDAT?

Ask them to. Many yards that start stocking KDAT report significant increases in treated wood sales — in some cases tripling volume within the first year. Northern Crossarm offers a 90-day stocking dealer program that lets yards try KDAT Brown with no long-term obligation. Details at crossarm.com.

Ready to Spec KDAT for Your Next Build?

Whether you’re a deck builder looking for a more stable framing system, a lumberyard looking to upgrade your treated wood offering, or a homeowner wanting to understand what your contractor is specifying — KDAT lumber is the answer to the most common deck problems.

Northern Crossarm has been producing the finest KDAT in the country since 1922. We ship truckloads east of the Rocky Mountains and maintain one of the largest inventories of kiln dried treated lumber on the ground — approximately 15 million board feet at any given time.

Call us: 715-723-4100
Email: sales@crossarm.com
Web: crossarm.com
Quality Since 1922 · Chippewa Falls, WI · East of the Rockies

From battling harsh UV rays, battering rain and cold-warm weather temperature extremes, a quality wood deck can turn faded or dull. Fortunately, there’s a solution – a high-quality, water-based deck stain can revive a deck’s appearance while protecting against the elements. Learn how to choose the best deck sealer for your project.

What’s the difference between Stains Vs. Sealers

Both stains and sealers are very similar – they’re both usually comparable and contain the same ingredients. However, while sealers are normally transparent, stain seals help with imparting color into the wood. Both will repel water, and the highest-quality sealers always include UV blockers and fungal preventatives.

How about water-based stains Vs. Oil-Based Stains?

Unlike paint, deck stains do not remain on the surface. A high-quality wood stain is designed to penetrate wood while protecting your deck from the elements. A common choice is deciding whether to use a traditional oil-based deck stain or a newer, water-based stain to protect your deck.

Oil-Based Deck Stains

Oil-based deck stain naturally repels water, can take up to 2 days to dry after application, and usually requires a strong solvent like paint thinner for cleaning brushes and sprayers after use. Important to mention, oil-based stains are flammable when wet, so you should never smoke or apply near a source of fire such as a grill. Once dried, oil-based stain no longer poses any fire hazards.

Water-Based Deck Stains

The new kid on the block, water-based stains have become an extremely popular sealer option for wood decks. For one, it dries quickly – with a water-based stain you only wait two or three hours maximum, vs. the 48 hours an oil-based stain takes to dry. It also cleans up easily with soap and water and doesn’t require harsh chemicals to clean brushes, rollers or sprayers. Water-based sealers feature low VOC levels (volatile organic chemicals), so it’s also a more environmentally friendly option with fewer fumes than an oil-based stain. Typically, water-based sealers will cost more than an oil-based stain, but the benefits for selecting a water-based stain or sealer normally outweigh oil-based stains on many levels.

Opacity & Pigments

The reality is, people love the look of a rich, brown deck. For this reason, selecting a deck stain opacity (pigment level) is extremely important, especially if you’re staining or sealing over an existing, colored deck. Opacity also helps to determine how well the product can protect your deck and how soon it may take to reapply. Another thing to consider with pigment is that you’ll see less of that beautiful wood grain once it’s applied.

Deck Stains are available in four opacities:

Toner – Toner is the closest to a clear sealer. It will contain just a hint of color that only leaves a partial hue to the wood. This is a very popular option, as it won’t change the overall look of your deck, but still adds many protective qualities that homeowners enjoy. When using toner, you’ll normally have to reapply yearly for the best protection.

Semi Transparent – Of all opacity levels, semi-transparent deck sealers are the best selling. A high-quality semi-transparent deck sealer will add color to your deck, but will still allow the wood grain to show through. It’s the best of both worlds – keep the beautiful look of wood, while adding color and protection. A re-coat of semi-transparent sealer will also sustain longer, normally giving a homeowner three to four years before having to reapply.

Semi-Opaque – Also known as “semi-solid”, a semi-opaque stain contains enough pigment to add a rich color, but also obscuring most of the wood grain. Similar to a semi-transparent stain or deck sealer, you’ll have to re-coat every few years.

Opaque – Also called “solid”, an opaque stain will have the most pigment and protect the wood the longest. You’ll only need to re-coat usually every four to five years, but it is usually extremely dense – opaque stains will hide wood grain completely, but it’s still a popular option for color and protection when sealing your deck.

Water, UV & Fungi Protection

High-quality deck stains and deck sealers (both water-based and oil-base) will offer water protection. They’ll repel water and prevent rain from saturating your wood deck in order to minimize wood’s natural tendency to swell, warp and rot. However, the best stains will also offer protection against Harmful UV rays to reduce surface problems like cracks, checking and splintering. And finally, there will usually be a fungi preventative which helps against mold and mildew, which can lead to wood rot. Adding these ingredients will typically increase the cost of a gallon of stain, but it’s an important sacrifice that most homeowners are willing to pay in order to increase the longevity of their decks.

About Northern KDAT Deck Sealer

Northern KDAT Deck Sealer is a durable, lasting wood finish that protects against the damaging effects of water, fungi and UV radiation on all types of wood surfaces including cedar, redwood, pressure-treated wood and composite lumber.

VOC-compliant, this more environmentally-friendly, water-based sealer features a beautiful matte finish and is fortified with transparent oxide-based nanoparticles. With over 30 TRILLION nanoparticles per square inch, Northern KDAT Deck Sealer provides unmatched all-weather protection for your deck.

Northern KDAT Deck Sealer Benefits:

• Recommended for Northern KDAT Decking
• Protects the appearance of Lumber, leaving the gorgeous natural wood grains in wood.
• Enhances the performance of pressure treated wood, giving it a longer life cycle as well as resistance against UV rays, fungi and water-saturation problems.
• 100-150 sq. ft. of coverage per gallon (2 coats).

Definition: Kiln Dried After Treatment Lumber (KDAT) is a drying process that occurs after pressure treating wood – once lumber is pressure treated with chemicals, kiln drying removes excess moisture and chemicals left behind to help minimize the natural tendencies of wood to warp, cup and shrink.

KDAT Lumber Benefits?

• Can be painted, stained, or sealed immediately without waiting.
• Even drying minimizes cups, warps, checks and shrinks
• Easier to handle, cut and plane
• Lighter than “wet” or “green” treated lumber
• More nail-holding and screw-holding power
• Easier to drill and saw

How is KDAT Pressure Treated Wood Process Different?

KDAT wood is treated similarly to “green” or “wet” wood with one key difference – after KDAT wood has been pressurized with chemicals, it goes through an extra drying step in a kiln. Using controlled temperatures, the lumber is stacked to provide airflow between each board and to ensure uniform drying. Traditional “wet” or “green” lumber that doesn’t undergo this process will take as long as 8 months to a year to dry out, usually causing problems with warps, cups, checks and shrinking over time. Once in the kiln, the moisture is reduced by as much as 80% to create a much drier piece of wood and those problematic characteristics are minimized in the process.

Switching to KDAT Because Of Composite Decking Deck Warp

One of the biggest reasons that contractors, customers and yards make the switch to KDAT over regular pressure-treated lumber have to do with the problematic issues associated with composite deck warp. As regular pressure-treated substructure shrinks, cups and warps (during the normal 8-month drying process), joists move, causing deck boards to twist and warp.

However, by using KDAT lumber, the joists natural characteristics to warp, cup twist are minimized, as the wood has already had most of the moisture removed. After all, moisture is the biggest issue associated with wood, but by using KDAT – there are fewer decking issues, callbacks and customer complaints.

Recommended KDAT Applications:

• Deck Boards, Deck Rails & Deck Substructure (Joists, Posts)
• Pergolas
• Fencing
• Boardwalks, marine construction
• Flatbed trailers
• Storage sheds

KDAT Wood Species & Sizes

Kiln Dried After Treatment wood is usually available as dimensional stock for rail components (2x4s, 2x6s, 4x4s, 6x6s and 2x2s). For decking, KDAT wood is typically available in 5/4x6s and 2x6s. And finally, for joists, stringers and beams, KDAT treated wood is commonly found in 2x8s, 2x10s and 2x12s.

Southern Yellow Pine – Also referred to as SYP, Southern pine is the most common deck framing material in the eastern United States. SYP is strong, stiff and yield a high proportion of sapwood which is ideal for absorbing preservative and chemicals.

Douglas Fir – Extremely strong and less prone to warps and splits (other than Southern Yellow Pine), this wood is predominantly found in the Western United States and Canada.

Red and Ponderosa Pine – Not as strong as Douglas Fir or Southern Yellow pine, but still good at absorbing preservatives. Found in the Northern United States and Canada.

Maintenance Costs of KDAT Vs. “Green” or “Wet” Treated Lumber?

On average, a typical “green” or “wet” pressure treated wood deck will need to be sanded, cleaned and stained and sealed every two to five years. This of course depends on the type of stain you use and what weather conditions your deck has been exposed to. Left untreated, a wood deck will fade and eventually rot.

Furthermore, a regular pressure treated deck is prone to warping, particularly in harsh climates.

Typical Maintenance of KDAT Lumber?

Similarly to wet lumber, Kiln Dried After Treatment lumber/wood sill also need to be sanded, cleaned and stained every two to five years. However, unlike traditional pressure treated wood, KDAT is much less prone to warp, twist, cup and check.

As a large percentage of moisture is removed from the wood prior to construction, boards are normally returned to as close to their dimensional size, leaving a product that is

KDAT Costs Compared to Composite and Cedar

One of the most common questions when it comes to Kiln Dried After Treatment wood is the cost. As you’ve maybe discovered by reading this article, there are many more benefits associated with KDAT wood that meets the eye. However, you’re probably thinking, that comes at a premium cost, right?

KDAT treated wood is typically 15-25% higher than traditional “wet” wood. Considering that the wood goes through an extra step (the drying process), it is considered to be a “specialty product.” However, some companies like Northern Crossarm Company go the extra step and add pre-finished brown, eliminating the need for routine deck maintenance for up to 4 years.

Compared to cedar (which demands premium 30%+ pricing differences compared to traditional wet lumber, KDAT usually sits in the middle between the high price of cedar and the low price of commodity lumber like green or wet pressure treated wood.

Common Pressure Treated Chemicals

Common pressure treating chemicals include “CCA, ACQ and MCA”. Chromated copper arsenate (CCA) has since been restricted in residential settings due to the health and environmental concerns of arsenic leaching out of the wood. A widely used alternative to CCA is ACQ, (alkaline coper quat). And finally, a greener, more commonly treating chemicals that’s gained wide momentum in recent years (MCA) or Micronized Copper Azole. Extremely versatile, MCA can be used in Above Ground, Ground Contact and Freshwater Contact applications. It’s a copper-based wood preservative and provides long-term protection of wood exposed in exterior applications

The Traditional Pressure Treating Process

Pressure-treated wood is immersed in a liquid preservative (commonly chemicals) and placed inside of a pressure chamber. Once inside the pressure chamber, the chemical preservative is forced into the wood fibers, effectively penetrating to the core of each piece of wood.

Wood is a porous material, which makes it ideal for the pressure treating process. Because it is porous, wood has a natural tendency to warp, cup, twist, crack, check, shrink and swell as it is exposed to wetting and drying cycles.

The pressure treating process fully saturates wood with preservative and water. While the preservative is left in the wood for protection, the water is released as the wood naturally dries, bringing out these natural characteristics.

Kiln Dried After Treatment, “KDAT” is a process that removes this excess moisture from wood introduced by the treating process. Kiln drying after treatment helps to improve the performance and stability of pressure treated wood.

KDAT Benefits:

• Lighter, easier to handle.
• More resistant to shrink, cup & warp.
• Easier to saw & plane.
• Better holding power (nails & screws).
• AG, GC & Fresh Water Immersion.
• Can be painted or stained immediately.
• Better corrosion resistance for exterior code-approved fasteners & hardware.

KDAT is Still Pressure Treated Wood.

While the KDAT process helps to improve the stability of pressure treated wood, it does not make it impervious to wood’s natural characteristics. This is especially true if it is exposed to wetting and dry cycles prior to installation.

What Not To Expect?

Strict Uniformity – Sawn lumber will vary in dimensional size due to mill inconsistencies. KDAT can only restore lumber sizes close to their beginning size. IT IS NOT EXACT.

Exact Moisture Content – When lumber is KDAT, a moisture range of (125%-19%) is targeted. KDAT is not an exact science, and lumber will have variations in moisture content. Moisture variations will become considerable, if the lumber is exposed to moisture after being Kiln Dried After Treatment.

Elimination of All Natural Characteristics – While KDAT improves the performance of treated lumber, it cannot eliminate these natural characteristics completely. Some warp, cup, twist, check, crack, shrink and swell is to be expected.

Because wood absorbs moisture and swells when exposed to moisture, proper spacing between deck boards is important during construction when using KDAT decking. A gap of approximately 3/8″ between boards allows for expansion.