What is KDAT Lumber? The Complete Guide to Kiln Dried After Treatment Wood

by | Mar 30, 2026 | Uncategorized

What Is KDAT Lumber? The Complete Guide to Kiln Dried After Treatment Wood

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:

Feature KDAT Lumber Green / Wet Lumber
Moisture content at install 12–19% 50–80%+
Drying time before staining None — stain immediately 8–12 months
Warp, cup & twist tendency Minimized High during drying
Weight on the job site Lighter — easier to handle Heavy and saturated
Nail & screw holding power Better Reduced when wet
Composite deck compatibility Ideal — stable substructure Problematic — joists move
Pre-finished option available Yes — Brown & Grey (Revere) No
Callback risk Low Higher

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