Green Lumber or Kiln Dried Lumber: Which Kind Do You Need?

Forestry, done well, is a combination of science and nature which results in strong, durable wood. However, all wood species are harvested in the “green” condition, which is a term for the properties which behold wood in the wild.

There’s Green Wood

building with green lumberMany observers would be shocked at the high (“green”) moisture content (MC) of some wood species. Since trees comprise an autonomous eco-system of water and nutrients, it stands to reason that sapwood (the layer next to the bark) is generally higher in MC than heartwood (inner wood which has died). Sapwood distributes water and nutrition through a tree. The heartwood, or inner wood, becomes infiltrated with gums, resins, and other materials.

This makes it more resistant to moisture flow and thus, the heartwood usually requires longer drying times than sapwood. Sapwood and heartwood will affect the drying curves for each wood species.

A wood’s MC is also a dynamic exchange between the wood itself and the surrounding air. When the relative humidity (RH) in the air rises, wood absorbs moisture from the air; when the RH falls, wood releases moisture into the air. This occurs naturally, and it occurs throughout a wood product’s lifespan even after it has been harvested and kiln-dried for human use. Wood producers, builders, and consumers need not fret over such an organic, natural process, but a thorough knowledge of it will guarantee success with wood in all sorts of product applications.

The key to wood strength and performance over time is to dry the wood appropriately to its optimum MC depending upon the end product’s service conditions and the end product’s installation destination.

There’s Kiln-Dried Wood

Kiln Dried lumber

Wood in “green” condition must be kiln-dried in order to be used as construction grade lumber for building purposes, as an example. Lumber production is a complex process in which green timber is sawn, dried and processed. The natural air-drying of lumber can be a long process, so oftentimes lumber will be kiln-dried to speed the process along. Kiln-drying is basically a process of placing sawn lumber into kilns where heated air is circulated and the temperature and RH of the kiln is controlled for the purpose of reaching the wood’s equilibrium moisture content (EMC): a balance between the MC of the wood, and the RH of its surrounding environment, depending upon the end wood products application specifications. Once the EMC is achieved, a wood’s MC can vary with slight changes in the RH of the surrounding environment without jeopardizing the strength and structural integrity of the end wood product.

Lumber producers deploy expansive and expensive wood MC control systems at all phases of wood production. Kilns are an integral part of the wood’s MC measurement and management process, as the kiln-drying procedure is where the green lumber is dried to its optimum EMC.

There’s a Moisture Meter to Measure It

A wood moisture meter is crucial in establishing and maintaining healthy wood MC levels at each stage of lumber production. A wood moisture meter is a tool which measures the wood’s MC. As green wood circulates for processing in a mill, in-kiln and in-line MC systems measure and document the wood’s MC and track the efficiency of the kiln-drying process. Professionals carefully monitor and control the process to optimize the harvest. Kiln operators and quality control personnel deploy hand-held wood moisture meter products to conduct as many spot-checks as needed to verify the mill’s kiln-drying efficiency.

Ecology is merging with forestry in the modern era to make MC measurement and control an ongoing matter of wood maintenance. Wagner Meters, a family-run industry leader in MC measurement technology, has developed several wood moisture meter products to assist industry specialists, retailers, wood flooring installers and owners and hobbyists in protecting their investments.

As the world awakens to its own nature, wood moisture meter technology has advanced greatly. Wagner Meters features pocket size digital and analog styles of its wood moisture meter products. Now there’s a cost-effective, reliable wood moisture meter to suit any wood measurement application goal, from the home to the lumber producing mills.

To learn more call: 800-634-9961.


Free Download – How to Choose the Right Industrial Hand-held Moisture Meter for Your Mill

Last updated on June 8th, 2021

29 Comments

  1. landscaper says:

    Thanks for the information. I’ll be sure to share it with our team!

  2. Dominic Guagliardo says:

    Hi Larry, the Amish built sheds in our area use rough cut lumber. Is there any disadvantage to this as a buyer? Do they come with any potential problems? Any information would be appreciated
    Dom

    • Larry Loffer says:

      Hi Dominic,

      Structurally, rough-cut lumber is as good as planed lumber as long as the lumber was dried properly. For an outdoor shed, the moisture content isn’t as critical. You might see warps, twists, etc if the lumber wasn’t dried prior to building the sheds. Rough cut lumber can be difficult to paint and/or stain.

  3. Deborah says:

    This topic always gets a mixed response within the log cabin industry, depending on who you speak to. There is much debate surrounding which logs to use to build a log cabin, from the species of tree that you choose, to whether you should use dead standing or green logs, kiln or air-dried logs. Freshly cut trees have high moisture content, and if they are used to build a log cabin immediately, the logs will have a tendency to warp, shrink and twist causing the log cabin to be less structurally sound. That’s why most people choose to dry their logs out before building a log cabin, which allows them time to stabilize, there are a few different methods of doing this; kiln drying them, air drying them. The other option is just to use the dead standing as soon as they’ve been harvested. Some professional builders argue that air drying logs is the best option whereas other are adamant that kiln dried logs are more stable. If logs are air dried correctly, and for the right length of time, they will reach the same equilibrium moisture content as kiln dried longs. While there are plenty of reasons for and against each method, it really does fall down to which method you prefer, your timeframes and budget.

  4. Charles Olson says:

    In 1978 I built my own home and contracted out some work. I hired framers to dry-in the house. When talking to them they told me I could save money by using green lumber. And yes there was a big difference in price. I ordered the lumber and it was delivered, but then the framers were delayed about 3 weeks which left this green lumber bundled at the job site. When they unpacked it all the inner wood had turned green or black. They said that is normal and built the house. So my lumber is black now!!! When inspectors come they always note a moisture problem in my crawl space, which I don’t have, so I take them to the attic and show them the roof rafters.

    Oh well, my observation was a few boards warped and I fixed them buy cutting and putting a long splint on each side. No problem in 40 years.

    But I always thought the green lumber had more structural strength which is contrary to information I’m reading now. My observation is that my green lumber is much harder than kiln dried lumber I get now. My old green lumber is so hard it is difficult to drive a nail in it without bending it. I only use screws now! I also noted that the green wood I removed for renovations over the years is much harder to saw.

    Could you help me understand why articles do not mention how hard green lumber gets? And does this hardness make it stronger? And why is my green lumber so hard?

    • Tony Morgan says:

      Charles,

      Air-dried lumber is more stable than kiln-dried lumber because it’s not forced dried through high temperatures, but rather a natural slower process. As the timber air dries the cells collapse, slowly causing them to compress and stay put, so when air-dried lumber absorbs moisture, it doesn’t swell as much hence it becomes more stable.
      Kiln-dried is a forced but controlled process where humidity and temperature are controlled using steam and fans for drying, because of its fast drying due to high temperatures, the cells collapse quickly rather than slowly as it would with air drying.

      Thanks.

  5. Paul Helvig says:

    Is it possible with the Dual Depth feature of the newer moisture meters to detect Case Hardened lumber?

  6. Chris Houghton says:

    Hello Larry,
    I have to fix a floor joist that in the basement supporting the first floor. The joist is 13 feet supported at both ends. The rot extends about 4 feet from one end. Because I cannot get a 2x8x13 board into my basement and put it in place, I will be trying a 12 foot length and possibly a 10 foot length and sistering it to the existing joist, which is in good shape other than the last 4 feet, and supporting just one end of the new joist, shimming as necessary.

    The existing joist is 2×8 Fir and is slightly larger than the modern green boards. My question to you is should I use a green board or either a kiln-dried or air-dried board to avoid crowning and shrinkage as the new board dries? My local lumber yard tells me that dried lumber has to be special ordered and could take up to 3 weeks to obtain.

    Thanks for any help you can extend.

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