Greetings! Have just begun to delve into timber frames and have formed a question. Since the frames were traditionally built from "green" lumber, what are they built from now? If they are still built from green wood, how do you make allowances for dimensional changes if you enclose the thing in one of those structural panel skins which isn't likely to give much?

This is a deceptively simple question.

Historically, buildings were less well insulated and far from airtight, so timbers that were locked together were allowed to dry slowly in situ. Many's the contemporary timberframer who has put up a frame in the Fall, slammed on the stress skins and turned up the furnace so that the rest of the trades could work indoors for the winter (and so that the homeowner could get out from under that bridge loan and into the house and a mortgage as soon as possible.)

This haste has generated all manner of tales about loud and violent checking (especially in low-quality timber) and prodigious amounts on moisture forming on the inside of the windows (especially)and upon every other hard surface. This is less of an immediate problem when an air to air heat exchanger has been installed (as many contemporary timberframers recommend). Still, the timbers do seem to twist and check more in houses that are tight and heated right after the frame goes up.

To combat this, some timberframers have invested heavily in salvage wood (a by-product of the Malling of America). Heavy timber of excellent quality can be found in the framing systems of old industrial buildings. Also various drying technologies are turning up the heat, so to speak, on fresh-sawn timbers. One effective method combines microwaves and a vacuum dehumidifier in large reinforced steel caverns.

None of this comes without an upcharge, and some suggest that there is a political and enviornmental cost, as well. Salvage and kiln-dried timbers are always more expensive than fresh-sawn; harder to find, harder to cut, etc., and there is almost always a much higher waste factor, as well.

Hope this helps.

Soooo....The frames are still often constructed of "green" lumber for purposes of ecomony? Is large size kiln-dried lumber a commonly available item or is it a specialty all its' own? My question stemmed more from the fact that having studied log home construction a bit. With these, it is common construction practice to make various mechanical allowances around wall openings and interior walls and such to allow for a prodigious amount of "settling". Just wondered how much change in dimesion is to be expected from a framed structure and or how it is accounted for.

Good morning, No activity in my sector so I thought Id stick my nose in here

You should remember that timber to all intents and purposes does not shrink along the grain. (less than one percent, assuming that it is stright grained, - like much of the timber in north America seems to be - unlike our English Oak)

The fact that we build our imberframes with the posts vertical, (thats the theory when we start out anyway), means that unlike the log builders, we do not need to allow for any mechanical settlement.

It is possible to predict the behavior of timber in terms of how it will change shape (kind version), distort / deform (unkind version), but a lot less easy to predict the extent/degree/ammount of movment.
Or rather I should say I dont know a fool-proof method of doing this, but I would suspect there are people who do, so lets here (sic) those ideas -

[This message has been edited by Bill Keir (edited 02-19-99).]

The USDA puts out a great fat thing called The Wood Handbook. It contains an astonishing amount of information about the mechanical properties of wood, including a chart by species that expresses shrinking as a percentage of size. You could look it up.

Dry wood almost always costs more than wet wood, and is usually more difficult to work. Someone had to own the stuff and hang onto for a while for it to dry naturally, your low-tech option, or someone else had to buy one of those great whacking whiz-bang kilns, pour megawatts of electricity through it and ship the resulting 'product' around the world.

More than a few quite servicable and lovely timber frames have been assembled from green or air-dried wood over the last thousand years or so.

It seems like my colleagues have pretty well covered the bases.
Bill Kier is correct in that timber shrinks much less in the longitudinal direction. Another difference in timber frames vs log homes is that the window and door openings are not cut in the timberframe itself. The openings are in the (usually more stable) enclosure system such as stress skin panels. So whne the frame moves, it does not immediately and directly effect the openings as would happen in a log building.
Joel's point is well taken on the difficulty of both obtaining and working dry timbers. I have discussed the kiln dried oak with one timberframe shop that did a major project uaing that wood. There were numerous tales of burnt drill bits and rolled chisel edges. The same shop also does a lot of work in recycled timber. The cost is higher than green timber, and again, it is more difficult to work.
The trade off being that the end result is more stable, and, at least with recycled timber, more socially responsible.
Another good book on the movement of wood is Bruce Hoadley's "understanding Wood". Included in the text is a method for calculating the shrinkage of wood.

Ah yes. Thank you gentlemen. Points well taken. The fact that most of the openings are in the "stable" skin would eliminate most of the settling problems. I assume that if the interior is drywall finished an owner could expect some cracking as things settle into place but that must be relatively minor compared to having a substantially "live" shell like you would in a log home. As for antique oak....with that I am well aquainted. I currently live in an 1840's vintage Greek Revival with an oak "balloon" frame. Broke many tools and fasteners while trying to tame a 12x12 corner post while replacing part of the sill. One other question if I may. I've seen decriptions of different surface treatments for timber frames ranging from hand hewn to planed. I have little experience dealing with green lumber so forgive my ignorance. Can you plane green lumber without making a mess of it? Or is that treatment reserved for more seasoned wood?

Green lumber can be planed very well. It's considerably easier that dry lumber. Fairly common practice is to work with planed green timber and beltsand off any dings or marks when fabrication is complete.

[This message has been edited by Grigg Mullen (edited 02-19-99).]

Hello all,

Just some more input. The treatment you speak of is the result of the process used to convert logs into timbers. Hand hewn refers to the result of squaring up logs with an ax, and finishing them with a broadax. Rough sawn finish is the result of making timbers on a sawmill.

Planing timbers is generally done with a hand plane, a portable power planer or a large stationary planer. The largest of these can plane all for sides of a timeber to dimension and square in one pass. The timber has already been squared up on a sawmill before it is planed. In all cases it is easier to plane green wood, but as it continues to dry the grain will raise some, depending on species.

For the most part, planing is done to faciltate applying a finish to the timbers. It is more predictable, and requires less oil (or whatever you are using). It should be noted that apllying finish to green would require an understanding of how the finish will react to the drying. Oil finishes are less likely to cause a problem.

Good luck with your research.

I know this is an old thread but the question is along the same lines so I'll continue this thread.

I have an existing, one floor extention on my house which I am planning to add onto this summer by removing the roof, putting on a second floor made of 4x8 timbers and then putting a new roof on.

Should I get green lumber now and let it air dry until August (when I plan to do the work) or should I wait until August to get the timbers and put them in green.

If I get the timbers now they will be white oak. If I wait until August they will be red oak.

Or should I try to get the timbers kiln dried?

But I believe that it will cost you so much more to have them dried or to try to buy dry timbers.
It really depend on a lot of things, which you should use.
Is the first floor area timber framed?
Will the second floor have exposed posts and timbers including rafters?
Or are you just using the 4x8s for joists for the appearance of a timber framed ceiling for the first floor?
If you are doing the last, then try for dry timbers as these size timbers green will shrink and this could upset installed sheet rock on the walls and floor boards on the second floor. Plus if you don't do the joinery right you could have problems.
Green hardwood cuts easier than dry. If you get green now and you don't store them properly then they could twist, bow or do other things.
When green timbers are cut and assembled shortly thereafter, then they are held in place by the joinery and have less chance to twist, bow and do other things, which could upset the assembly process.
I'm sure others will have some advice for you also.
Good luck with your project, and keep asking questions.
Jim

The current structure is a "conventional" 2x6 based frame.

The second story will basically be a 2x10 framed roof supported off of the new floor so mostly this is for appearance.

Is it the width of the timbers that is an issue here? Would 6x7 timbers be less likely to present problems?

If I can't get timbers which are already dry, how long will I need to put up green timbers before they are stable? I'm guessing from now till August won't really be long enough.

My thought was to install 6x8 beams along the top of the sill of the existing first story and then hang the 4x8 joists off of this using a half-lap joint. Reasonable?

I will certainly do so. Thanks for the feedback.

Chris:
If there is to be no living space on the second floor and if I understand you correctly and that the roof will sit on the ceiling of the first floor then the size of the ceiling joists aren't really that important.
If there is to be living space on the second floor then the first floor ceiling joists have to be designed for that second floor, floor load. And they are not ceiling joist but floor joists for the second floor.
I'm not qualified to suggest to you the correct size timber needed for the second situation. You should consult a timber frame designer who can properly design your 'new' roof, second floor arrangement.
The factors that will determine the size of the timbers are type of wood, span, spacing, load(s), and to some extent joinery methods. There are a lot of factors involved, and I probably missed some also.
Q: "If I can't get timbers which are already dry, how long will I need to put up green timbers before they are stable? I'm guessing from now till August won't really be long enough."
A: Air drying wood is figured on one inch in depth per year. So a 4x8 air dried would take at least four years. That's outside, stacked properly.
Q: "My thought was to install 6x8 beams along the top of the sill of the existing first story and then hang the 4x8 joists off of this using a half-lap joint. Reasonable?"
A: I'd have to assume you mean to install the 6x8 along the plate. Sills are at the bottom of the house were the walls met the foundation. Plates are at the top of the wall were the walls met the ceiling.
And then hang the new "ceiling" joists from the new plate timbers. Is this correct?
If this is the case and there is to be no living space on the second floor then this could work.
However your joist ends will have to be prepared properly to eliminate a potential point of fracture.
As I don't currently have a web page address where I can post you a picture to then import into this post, I'll email you directly a suggested sample joist end. A simple half lap joint could be a incorrect ceiling joist end. And it could crack at the ends.
Good luck, Jim

The second floor will actually be living space so the ceiling/floor joists need to be sufficient to support that load. The span is 15.5 feet from outside wall to outside wall and based on local guidelines for 2x8 floor joists, 4x8 oak beams at 32 IOC should be more than sufficient.

Yes, sorry, I did mean plate and not sill.

Thanks for the suggestion on the joist end. I look forward to that.

Chris,

I'm very concerned about the floor system you intend to fabricate. 15'-6" is a tremendous span for any floor system! Even 2x8's 12" OC would require a very high grade of lumber. I used the joist tables in the CABO code book for a quick check and SYP #1 is the only thing that would even make it in conventional framing. No grade of SPF even comes close.

2x10 conventional framing works much better, but you still need to remember the allowable deflection at 15'-6" is over 1/2". That's a "springy" floor unless you increase the depth of section sufficiently or use a much stiffer wood.

The other problem I would consider is using the same depth plates as joists. You can't fully house the joists unless you cut a "gain" on them, and even then you will only have a sliver of wood under the housing in the plate. The other problem is having to cut your soffit tenon halfway up the joist to hit the nuetral axis of the plate. You are going to be dealing with a lot of shear at the ends of these long span joists. I use "bearing members 2" deeper" as a rule of thumb.

I would strongly suggest hiring someone to correctly design your floor deck. It will be money well spent. Don't rely on local "code" for your guidlines. Remember what the sage John Abrahms told us: "Building to code means if it's built any worse it's illegal."

Concerned for your safety and QOL.

Rudy

Hi new to the forum. I am building a hybird cabin. I will be stick building the walls and using timbers for the second floor joist and all roof rafters. Help would be appreciated.

I do not have the time to properly air dry my lumber. I have the choice of either Yellow Pine or White Pine. Which do you recommend? It will be locally sawn with nominal dimensions.

Will WP span 14 feet using 4x8 or do I need to go to 6x8 for floor joists?

Some of the porch rafters which are 3/12 pitch will be 16' long. Will 4x8 work in WP or will they also sag? What if I gouge out the middle and slide a flitch plate inside and try to hide it?

I also have some porch beams that I will be running in pairs 16' out from the house to stone columns. Craftsman style. On top of these will sit 2x10s or 12s PT, 16" oc for the porch joist. Will WP span 16' with a 4x12 or am I crazy?

Thanks for the help.

Mr. Nut,

There is quite a range in design values (from good to terrible) for white and yellow pine depending on grade. The Timber Frame Joinery & Design Handbook, available here on the website, includes tables that will give you the numbers for each. You will need to be able to grade the timber yourself if you don't pay a grader to do it. For that you want to get a copy of a grading handbook and learn the grading rules.

The Northeastern Lumber Manufacturers Association (NELMA) handbook is good for white pine. You can get a copy for under $10 by calling them at 207-289-6901.

Once you determine the grade you need, you can see if it's available locally or not.

Good luck,

Rudy