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Green vs. Dried Timbers – That is the Question?

I often get asked if it is okay to use green, or freshly cut timbers, for a timber frame. In fact, the majority of the frames that go up today are cut and raised without going into a kiln or going through the process of being air-dried. Before the advent of kilns to dry the wood, all of the timber frames (for thousands of years) have been green or air-dried, with most of those being green timbers. So, which is best: green vs. dried timbers?

Green vs. Dried Timbers - That is the QuestionThe engineers consider anything over 19% moisture content to be green timbers. Having been in the shop for a number of years, I can remember having to dry off my chisel after cleaning a mortise because there was so much moisture in a timber. It is common to use green wood for a couple of reasons such as cost and extended lead times. If dried timber is preferred, the process can be done in several different ways and can produce a really stable wood if done correctly.

Green vs. Dried Timbers

  • Air-drying is by far the cheapest and easiest way to dry timbers. You are not using energy except for what the sun gives you. However, the catch is that on average, it takes about a year per inch to dry. So if you have an 8×8 post it would take 4 years to dry all the way through; and, depending on where you are, it may not be able to get below the 19% range.
  • Traditional kilns that dry the majority of the conventional framing, siding and trim can be used to dry timbers effectively. However, they have to be used at a low temperature for weeks on end to really do an effective job. Unfortunately, this uses quite a bit of energy and therefore costs money. If done too fast, it may cause the outside to dry too fast leaving the inside with too much moisture.
  • Radio frequency kilns are the best choice for kiln drying timbers. There are only a couple of them around and therefore drying timber this way is very expensive. They work like a microwave oven, which basically dries the timbers from the inside out.

Green vs. Dried Timbers in ConstructionWhen using green timbers, you will need to give special consideration to the joinery to make sure you take into account the shrinking of the timbers. Depending on the species of timbers you choose, and the moisture content of it when it was cut, you may have up to ¼” shrinkage in some places. Some of the joinery used in timber framing relies on one part bearing on another part to transfer loads, such as a beam resting in a mortise in a post, or a rafter landing on a plate. Thinking through the process the timbers will go through as they dry in your home or porch will help you make good joinery decisions. A couple of suggestions:

  • On post and beam situations, move the pegs closer down to the bearing surface between the post and beam. This will allow the beam to stay closer to the bottom of the housing in the post over time.
  • Where a housed rafter dives into a plate, cut an extra 1/8” off the bird’s mouth so the rafter will always bear on the housing and not the rafter tail.

In the end, the choice will be up to you to decide on whether or not your timber is dried or left green. For both of my personal timber frame projects, I chose to go with green timbers and have not regretted the decision. Timber frames have certainly stood the test of time before the advent of the kilns.

joinery details Green vs. Dried Timbers

22 thoughts on “Green vs. Dried Timbers – That is the Question?”

  1. Some of my neighbors are building a cabin up in the mountains. I heard them discussing the other day about whether they should use green wood or dry timber. It’s very interesting that there are different species of timbers.

  2. We have a large yard full of White Oak timbers of many widths and lengths that were cut to build a timber frame home. The project fell through and the timbers have been air drying for 13 years. We are planning on selling them and wonder if the air drying of all those years adds an extra value to them? I take it that it is an uncommon situation as I can’t find any info that would help figure out the value.
    Would greatly appreciate any advice! Thank you!

    1. It can add value and character to the wood but it will depend on how they were stored. They will likely need some work done to them before use but aired dried white oak timber are worth something more than green timbers. If they don’t have any sapwood and it is all heartwood then the boat building industry may pay the most.

      1. SFC Steven M Barry USA RET

        Thank you for your response to my wife.

        The timbers in question amount to about 41,000 board feet; around 90% white oak, the rest red oak. Some are cut (for a frame the was canceled), the rest are uncut. Sizes range from 4×6 to 14×14, lengths from 12 feet to 16 feet. Most have the usual checks and shakes one would expect from air drying; some (obviously cut from tension wood — grr…) are bowed, some twisted, some both (invariably the smaller dimensions). Sap wood is “frassing” (as the Brits say), but when draw knifed and brushed the heart wood is sound (in Europe this is not considered a defect — I cut a Medieval frame — scribed — with timbers recycled from the canceled frame; the “wavy” edges add some “olde world” charm to it). Anyhow, the big question is what is the market value of the “well seasoned” oak timers? They were got green at around $1.00 per board foot a little over 13 years ago. I’ve seen sites offering “reclaimed” and “vintage timbers” averaging $4.50 per bf (or more). So, the question is, in your opinion, what would be a fair asking price for them?

    2. I am sorry to be somewhat rhetorical, but your request price would be the price that the top purchaser would offer. There are too many variables, like did you elevate your timbers to dry, did you already mill them, have a cover over your timbers, did you use at least 1″ stickers, was there any infestation during drying, any mold, how will the timbers go from your place to the next place. Unless your timbers are already milled, you may find that you would need to pay somebody to remove them, so you may be better to just cut, split, stack, and keep your winter warm via your woodstove.

  3. How long after timbers are cut til they really start to move on you? We are cutting white oak timbers for a frame this fall and hope to put it up early spring in Nebraska. Once they’re milled and joints cut are they going to move too much over the winter to put together?

    1. They can start to move as soon as you cut them. I would end seal the timbers asap with Anchor Seal and then stack them up with stickers and the heaviest timbers up top.

  4. I live in North Carolina and I can’t get timber from my property approved to build with unless it is below the 19%. I plan to build a kiln to dry my timbers in to speed up the process. Is it better to rough cut the timbers to dimension before drying or dry the log and then cut to rough dimensions? I know that the timber will shrink a bit during the drying process but I figured if I leave enough excess in each direction it will get me close to where I can dimension it to actual size.

    1. Matthew Stevens

      Hummmm, I would challenge them on 19% and see where that number came from. Also, where in NC? I would recommend full size before drying and then milling them down to their final size in case they move during drying. You can also get an engineer to look at the frame and stamp them for greenwood use, that would supersede you local code office. Let us know how we can help.

      1. I live up in the mountains in WNC. In the residential code that ungraded lumber can be used but the way its written, its kind of confusing.

        Can ungraded lumber be used if the lumber is cut from the homeowner’s site?
        Yes, as an alternate material and method according to Section 105 of the 2012 Administrative
        Code. Ungraded, unstamped lumber may be used for the construction of a house or accessory
        building on the owner’s land if:
        1. The timber is cut from the owner’s land.
        2. The structure shall be occupied by the owner or a member of his immediate family for a
        period of at least one year after the Certificate of Occupancy is issued.
        3. The lumber shall meet the 19 percent moisture content requirement at the time of
        construction. The lumber must be air dried for 90 days or kiln dried.
        4. The homeowner contacts the local building inspection department before the timber is cut
        to verify the source and use of the timber.”

        This was released in 2012 as an Informal Code Interpretation from section 602.1 in NC Residential Code.

        1. The best thing to do is #4. While this is written in the 2012 Admin Code, I have found that the various code offices have their own rules for using non-graded timbers. I would like to add two other paths for you. The first is to find an engineer that will sign off on your timbers, an engineers stamp is a powerful thing at the code offices because they have a good path of responsibility. The other is to get the timbers graded on site. This is not as expensive as it sounds but tends to be a lot of material handling.

    2. A bit late to the thread, but if it may help someone else- its extra labor but I would not dry the log. I would square it to within an inch of your final need, then dry those cants and resaw true later. It will save you a lot of time to get rid of the unneeded green slabwood.

  5. When you say to allow 1/4″ shrinkage… what length is this related to? I am potentially looking at 20 foot green cypress beam as top chord of a truss.. remainder of truss (chords and webbing) air dried for a couple of years… all 2″ thick…. i have run short of my own stuff unfortunately…

  6. Natalie DuBois

    Do connectors such as the Rothoblass Alumini have any issues when build with green timber? Any issues with them pulling out as the timbers dry out?
    I’m interested in trying them out on a project, but am concerned with this issue.

    1. Matthew Stevens

      That is a valid concern. We use them in conjunction with housings to minimize any issues. The problem with using a rigid connector with greenwood is the connector cannot move with the wood.

  7. Not much discussion of using previously used timbers (salvaged, recycled, or antique). I have been using them since 1990 with pretty good results. Nice and stable to showcase craftsmanship a little better and we are not cutting as much of our somewhat poorly managed forests. We do try to charge a lot tho, like that $4.50/BF range.

  8. Cindy Watkins

    Reading your discussion is infomative and interesting. I have wanted to be part of buiding a timber frame for myself in Oregon, but managing a build from six hundred miles away seemed to be too much project for me. So I am considering and looking at homes that are for sale. It’s not the same but I can live with not having to make so many decisions on everything from location to soil type to shingles and codes. Thank you for sharing!

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