Timber Framing: Dry or Green?

      Thoughts and opinions on whether to frame with dry lumber or green, and whether to let felled logs dry before sawing. October 1, 2009

Question
I'm in the planning stage of building a timber frame home and I'm looking for individuals in WV who are familiar with layout and cutting for timber framing. I will be sawing the timbers myself since I have 135 acres of 60+ years of timber growth and a Wood-Mizer mill. Also, how long should the timbers dry before laying out the framing?

Forum Responses
(Sawing and Drying Forum)
From contributor A:
Hardwood or softwood? Softwood I like to sit about 3 to 6 months. Hardwoods I like to fit within 3 months of sawing. Saw the largest timbers first, as well as the longest ones.



From contributor E:
For my WI timber frame, I logged and milled all of the white pine and red oak timbers during August 2005. I barely stayed ahead of the crew that did the mortise and tenon. They took some of them straight off the mill. They were done in September and we raised the frame on October 1. If they sit too long, you will lose your flat faces as they split, which would make it tough to measure your angles for mortise and tenon.


From the original questioner:
Thanks! Since I have access to both softwood and hardwood I would expect there is a place for each. Sounds like once the framers are in place there's little time to waste in sawing timbers. I think with a 30-60 day span between sawing and framing I could probably keep up.


From contributor T:
Here in Montana I have worked with both dry and fresh timbers, usually ponderosa pine or Douglas fir. I have found that the sooner the better - the joints only get tighter from shrinking.


From contributor S:
The old timers would say that you should fell your trees now, while the sap is down. Then leave the trees in the woods with the tops and branches still attached. In the spring, the felled trees will leaf out and that will draw more moisture out of the wood. Then after the leaves on the felled trees dry up, buck up the logs and get them sawed.

I think this old story is mostly BS. The M/C of the heartwood of the log will be about the same, but many of those old timber frames are still around, so maybe there is something to it.



From contributor G:
My father was in the lumber business in the 40-50-60's and would cut trees all winter in central PA but not saw them till late spring and summer. He could sell his lumber when others could not - apparently it was better lumber than others in area. So contributor S must be either correct or close.


From contributor A:
The sap really never goes down. Trees are just as "wet" year round. The sugar content may change. The felled logs just laying in the woods will dry some but you have to remember that the job of bark is to keep moisture in the tree and everything else out.


From contributor S:
The responses to my post got me thinking. Here's an article I found, and it looks like my original opinion was well founded.

This is from the book "The Mechanical Properties of Wood", by Samuel J. Record, available from Amazon:

"Season Of Cutting
It is generally believed that winter-felled timber has decided advantages over that cut at other seasons of the year, and to that cause alone are frequently ascribed much greater durability, less liability to check and split, better color, and even increased strength and toughness. The conclusion from the various experiments made on the subject is that while the time of felling may, and often does, affect the properties of wood, such result is due to the weather conditions rather than to the condition of the wood.

There are two phases of this question. One is concerned with the physiological changes which might take place during the year in the wood of a living tree. The other deals with the purely physical results due to the weather, as differences in temperature, humidity, moisture, and other features to be mentioned later.

Those who adhere to the first view maintain that wood cut in summer is quite different in composition from that cut in winter. One opinion is that in summer the "sap is up," while in winter it is "down," consequently winter-felled timber is drier. A variation of this belief is that in summer the sap contains certain chemicals which affect the properties of wood and does not contain them in winter. Again it is sometimes asserted that wood is actually denser in winter than in summer, as part of the wood substance is dissolved out in the spring and used for plant food, being restored in the fall.

It is obvious that such views could apply only to sapwood, since it alone is in living condition at the time of cutting. Heartwood is dead wood and has almost no function in the existence of the tree other than the purely mechanical one of support. Heartwood does undergo changes, but they are gradual and almost entirely independent of the seasons.

Sapwood might reasonably be expected to respond to seasonal changes, and to some extent it does. Just beneath the bark there is a thin layer of cells which during the growing season have not attained their greatest density. With the exception of this one annual ring, or portion of one, the density of the wood substance of the sapwood is nearly the same the year round. Slight variations may occur due to impregnation with sugar and starch in the winter and its dissolution in the growing season. The time of cutting can have no material effect on the inherent strength and other mechanical properties of wood except in the outermost annual ring of growth.

The popular belief that sap is up in the spring and summer and is down in the winter has not been substantiated by experiment. There are seasonal differences in the composition of sap, but so far as the amount of sap in a tree is concerned there is fully as much, if not more, during the winter than in summer. Winter-cut wood is not drier, to begin with, than summer-felled - in reality, it is likely to be wetter.47

[Footnote 47: See Record, S.J.: Sap in relation to the properties of wood. Proc. Am. Wood Preservers' Assn., Baltimore, Md., 1913, pp. 160-166.
Kempfer, Wm. H.: The air-seasoning of timber. In Bul. 161, Am. Ry. Eng. Assn., 1913, p. 214.]

The important consideration in regard to this question is the series of circumstances attending the handling of the timber after it is felled. Wood dries more rapidly in summer than in winter, not because there is less moisture at one time than another, but because of the higher temperature in summer. This greater heat is often accompanied by low humidity, and conditions are favorable for the rapid removal of moisture from the exposed portions of wood. Wood dries by evaporation, and other things being equal, this will proceed much faster in hot weather than in cold.

It is a matter of common observation that when wood dries it shrinks, and if shrinkage is not uniform in all directions the material pulls apart, causing season checks. (See Fig. 27.) If evaporation proceeds more rapidly on the outside than inside, the greater shrinkage of the outer portions is bound to result in many checks, the number and size increasing with the degree of inequality of drying.

In cold weather, drying proceeds slowly but uniformly, thus allowing the wood elements to adjust themselves with the least amount of rupturing. In summer, drying proceeds rapidly and irregularly, so that material seasoned at that time is more likely to split and check.

There is less danger of sap rot when trees are felled in winter because the fungus does not grow in the very cold weather, and the lumber has a chance to season to below the danger point before the fungus gets a chance to attack it. If the logs in each case could be cut into lumber immediately after felling and given exactly the same treatment, for example, kiln-dried, no difference due to the season of cutting would be noted."



From Professor Gene Wengert, forum technical advisor:
Record's book was published 95 years ago. Since that time, it has been shown that wood properties do not vary with season. However, his comments about the weather affecting drying, staining, and fungal growth, were true then and they are now (or vice versa).


From contributor B:
And I was told by an old woodworker, back when I first started sawing trees into boards, that if you must cut a tree in a season other than winter, cut it in the phase of the moon when it was not pulling the sap up. I am not sure when that phase is, but it only makes sense that the extra gravitational pull of the moon would place more sap in the tree that would have to be dried out of it.


From Professor Gene Wengert, forum technical advisor:
When I was in Brazil a few years ago, the kiln operator there told me that you never want to start a kiln on a full moon. It had to do with the moon and the tides, etc. I asked him if he really believed that and he said, "No! But the boss does, so we get one day a month off."


From contributor A:
I have stated before that I saw on the phase of the moon. But then I also saw some products by the humidity of the day. I plant the garden by the moon as well. The moisture of the tree remains about the same throughout the year. Having sawed lots of logs up close and personal, you get to know your trees.

Logs that I spalt I try to buy the same time of year. I have found that buying logs in those two months produces the best product. Also trees with a left hand twist should be left for firewood.



From contributor Z:
I cut mostly mesquite logs. They are never very straight. I have one that has a right hand twist. Will it be okay?


From contributor A:
Most trees have a slight right hand twist. So sawing a log with straight or right hand twist is the norm. If you look at most hollow and bad trees they will have a left hand twist.


From contributor Z:
Just curious, but what causes the twist one way or the other? I know if a mesquite tree has a hard mushroom growing on the outside, it will be rotten inside.


From contributor A:
Maybe the Doc knows, but I would guess something in the DNA instead of environment. Just know what GrandPa taught and what I have seen in sawing logs.




From contributor B:
This is an example of a straight trunk - no twist. My biggest one yet - bur oak, 16'6", 42" diameter at the big end, and the small end was still 36". (A table and flooring.)


Click here for higher quality, full size image



From Professor Gene Wengert, forum technical advisor:
I have heard that the twist is related to the Coriolis force... a very small force that results in one revolution per day of weather low pressure areas, etc. (Incidentally, this force does not affect the spin of water going down a drain.) I have heard similar stories about left hand and right hand causing different wood quality effects. The truth is that genetics are what cause the spiral. Any lack of quality in the wood is also caused by genetics, but it is not related to the direction of the spiral. The previous comments about right hand spirals being okay and left hand not were based on personal observation (I believe), but it was just coincidental.


From contributor U:
Very interesting stuff! I am a little confused about right hand twist vs. left hand twist, but if I were looking at the end grain on the butt end of a fallen tree I can not think of one that had a counterclockwise twist, but rather always a clockwise twist if at all.

One of my very first customers years ago was an old local farmer, now in his mid 80's. He told me how logs used to be cut by the moon phases, and I politely listened with curiosity, not necessarily disbelief, but with raised eyebrows!

I have been reading Eric Sloane's books, which I highly recommend if you're interested in how things were done in early America, especially in wood. He touches on cutting with moon phases in the book "American Barns and Covered Bridges," but there does not seem to be any scientific reasoning behind this. I see how the moon affects the ocean's waters resulting in tides, and I remember in high school seeing a slideshow where, in some parts of the world, the tides fluctuate some 40+ feet every day from low point to high point.

Looking on a smaller scale, large lakes as far as I know do not have any fluctuations with the moon whatsoever, but maybe I am wrong. If a body of water as large as a lake does not have effects from the moon, why would a tree?



From contributor E:
My readings say that all lakes have tides, but they are generally too small to measure and/or are swamped by other water level influences. Back to wood, science may have identified important factors that control lumber characteristics, but that does not mean science has identified all influential factors. I used to laugh at holistic thinking, until I started learning more about agriculture. Whether those lessons apply to silviculture, I don't know, but the possibility deserves respect.


From contributor N:
Up here in the great white north, the full moon is usually in the coldest part of the month in the winter, so -30 is no time to try and saw. I've never paid any attention to the moon in the summer.


From Professor Gene Wengert, forum technical advisor:
The coldest time "up north" is when you can see the moon at night, as that means clear skies, a high pressure area which is always colder as the wind is from the NW, and lots of radiative cooling as well. The moon phases do not influence the outside temperature.


From contributor N:
I know there is no science behind it but the cold snaps seem to happen with a full moon more often than a new moon. At least they do here in central British Columbia. I must also admit that I have never documented this, just a general observation from twenty years working outside.


From Professor Gene Wengert, forum technical advisor:
If a cold snap occurs in BC, it is probably 5 days before it gets to WI and maybe a few more to get to the East Coast. By then a full moon has started to wane. Of course, if you get cold snaps every week (isn't that the truth about BC?), then I can understand what you have observed!

It is incorrect that the amount of sap in a tree changes with the season. The sap flows more aggressively in certain seasons, but the volume stays essentially the same. The idea that the sap is up in the summer and down in the winter is entirely incorrect.



From contributor P:
Dr Gene, I always enjoy reading your comments! I have a question regarding the sap being up or down. And that is: What causes the bark on many trees to peel easier from April through June?


From Professor Gene Wengert, forum technical advisor:
There is a layer of wood cells (actually several layers; in the old days it was thought to be a single layer) between the bark and the wood. These layers, called the cambium layer, make new cells on the outside that become bark and new cells on the inside that become wood. This layer is busy dividing in the springtime and this rapid growth makes the attachment between wood and bark very slippery.


From contributor P:
Dr. Gene, thank you so much for helping me understand what is happening in the tree. I'm building log/twig furniture and hopefully, a sawmill is in my near future! As soon as we can sell off a few things.

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