Seasoned and Preservative Treated Timbers

Just look for pressure treated lumber. You might be able to get in at a big box lumber company.

Real lumber compannies will carry it. I don't know about cost.

Treated wood will have the same shrinkage as non-treated wood.

You might want to try searching for "Engineered Lumber" or "Composite Lumber". There are manufacturers that take wood scrap and compress it into beams using a curable resin. It is very strong and very dense. It will still be affected by temperature, but might be spec'd by the manufacturer.

I don't know, but I would check these sites:

http://www.apawood.org/

http://www.woodbywy.com/

I think most of these sizes will be special order.

Preservative treatment will not affect shrinkage. (Note: you cannot cut treated wood without special safety equipment - the sawdust is a serious health and environmental hazard - so normally it is bought precut to size). Kiln dried lumber quality, and the type of wood chosen, determines the degree of shrinkage.

2X4, 2X6, 2X10, and wider plank lumber typically used as structural members are normally kiln dried to minimize shrinkage and warping and are widely available in any lumber yard - but you still have to pick through them to make sure they dried straight and free of checks or cracks, or you will end up sending half of it back and/or wasted. Planks which are 6, 8 or 10 inches thick are way over code and are not generally available afaik, so are likely a special order.

The framing lumber available in my area is softwood, mainly spruce and fir, but that would vary somewhat depending on your location, other woods may be widely available and/or preferred. A kiln dried hardwood lumber will shrink much less, and specific hardwoods, such as oak for example, make particularly good straight, strong and stable lumber. They are way too expensive to be used for ordinary framing in construction (anywhere on earth circa 2013), but if money is no object a kiln dried hardwood such as oak or maple would have much better resistance to shrinkage than the average softwood lumber, and would be the best choice for that objective. Some fairly thick planks (maybe 4-6 inch) are used for mantels or specialty products and might be available through a supplier of those high end finishing materials and products.

Considering the expense of kiln dried hardwood plank, and the certainty that exposed timbers are subject to expand, contract, crack, warp and require maintenance, you might be better off chosing metal or plastic as a building material.

The architect has already decided that this is to be timber. Nothing I can do to change it to steel or even composite lumber. Everything is exposed to view and to the elements, it is on the waterfront, so that is my concern about shrinkage and expansion.

I don't disagree that this should be made out of something totally different, but I'm just trying to make do with what I have. If it's even possible.

What is your role here? Are you the builder?

Is this new construction?

Has "the architect" done this many moment connections ever before?

Details, we need details.

Hmmm if you don't give details, you can't get the relevant answers. Salt water environment is very specific, creosote treatment is standard for wharf construction, and the big lumber is probably available pretreated. Is that what the architect had in mind? You still haven't mentioned what exactly you are building.

Two roofs. One is a gazebo roof with no interior supports or collar ties of any sort. So that is a tension ring. The other is a walkway roof, simple gable, that also has no collar ties. To provide any lateral stability I need to provide moment connections all over the place, which suck with timber but that's what it has to be. The only "easy" way to do moment connections with timber is by using kiln dried timber, this would also be inside a structure, so that there is no shrinkage/expansion after the timbers are in place which would lead to slack in the connection and therefore no more moment resisting capability. I've never done this for exterior timbers. That's why I'm wondering if you can get preservative treated, or some other type of treatment, that will be and stay <19% maximum moisture content. Is that possible? I've seen in some wood manuals that it is possible to get preservative treated and seasoned wood. Does anyone actually carry it on purpose or is it just treated wood that's been sitting in the yard for a while. Does this wood really stay at <19% maximum moisture content when exposed? If not then what is the point of it? Just to have seasoned treated lumber?

One reason for seasoning after treatment is that the material will be easier to handle because excess creosote has been weathered, assuming an outdoor 'seasoning' environment with some rain.

Some information about different treatment specifications and wood species:

http://www.extension.umn.edu/distribution/housingandclothing/dk0897.html

The oil based treatments are supposed to minimize water penetration, but obviously over the lifetime of the timbers that will eventually be lost. There is some relevant comment in a Delaware dept. of transportation pdf about bridge building (Timber Structures Design) I got from google.

"With the grain, average shrinkage values for green to oven dry conditions range between 0.1 and 0.2 percent; this is generally of no concern to the designer. Against the grain, shrinkage is much more pronounced. ...Dimensional stability is obtained by maintaining constant moisture content. Oil-based treatment methods provide dimensional stability by creating a water-resistant barrier on the wood surface. This reduces associated splitting and checking of the wood,...."

What is the design of your moment connections?

Our connections are plates top and bottom with 2-5/8"Ø shear plates and 3/4"Ø lags that are staggered top and bottom. Also a through bolt through the ridge to keep the plate from buckling.

Any other ideas?

Thanks for the link on selecting preservative treated wood. Always wondered how they chose "max 19% moisture content".

Well, I wasn't familiar with this concept in wood construction myself, so I did some reading - turned up a few documents where the type of connector was tested:

www.cmec.wsu.edu/publications/AndrewKrachtreport.pdf

cfs.nrcan.gc.ca/bookstore_pdfs/19352.pdf

These folks at UNB had improved results with tubular connections cw bolts (reduced splitting and checking). www.unb.ca/fredericton/forestry/wstc/_resources/pdf/unb2.pdf

None of these refer specifically to open air structures though. There may be something on it in this webinar: http://woodworks.org/resources/lateral-deflection-considerations-and-control-in-the-design-of-open-air-structures/

FEMA has some publications out there about construction in coastal areas, and the failures that occur - the links aren't readily copied but you will find em on google.

It's a strange thing that there aren't really any codes for building gazebos, sheds, hoop houses, other than the usual 'don't attach it to your house'.

You may be looking for solid or laminated timbers. These must be custom made and can be treated for exterior use. A search for laminated timbers might reveal one in your area.

All of these sizes are readily available from several sources here in Houston and along the Gulf Coast. There are hundreds of sources around the country, generally found near the coasts and large bodies of water. The species of wood is key to resisting shrinkage, the kiln drying process is key to straightness and reduced splitting. After posting a question here on CR4 (look in July 2012) about using these timbers for pilings, I did some more research and found that on the waterfront, unless you are doing extremely heavy (commercial, heavy vehicle traffic bridges, etc) you don't want steel, especially near the salt water. The cost is too high and the timbers perform better. http://www.gulfcoasttreated.com/treated-lumber http://www.gclhouston.com/prod_treatedtimbers.html http://www.ifphouston.com

Black locust is a hard wood. The lumber is naturally pest and rod resistant. Has a low shrink and swell rate.

Black and honey locust trees native to the US have been used by farmers for fence post. They last just about forever buried in the ground with out rotting off. Walk just about any old farms fence line and you will find them growing.

Occasionally I need a larger than normal quantity of wood for a project and don't want to spend "big box" prices.

I go straight to a local lumber mill.

There you can get rough-sawn timbers cut to size. A 6" x 6" will actually be that size.

They can also treat the wood for you.

I find that the total price is about 20% less than buying big box.

Back when heavy timber buildings were common, the connection of face to face joins was made using a steel ring between members with a threaded fastener in tension. This allowed air flow between members and reduced potential rot. Also allowed for tightning if needed. Any connection using end grain or side grain was plated. The rings used to be listed in Sweets Digest. Try Global Spec. The amount of movement in dried wood is not worth designing for. Treated is another story. Treatment seems to do strange things to wood. Splits, twists and warps as it dries, and not very stable. If you have to use treated, talk to a builder who has experience in the area.

Where I live, heavy timber buildings are the rule, not the exception. I have built several on my property without assistance. They are all farm buildings.

Since I live in Florida, I always use treated wood.

The wood will twist and warp as you say unless you erect it when you get it...can't wait even 3 days.

Once properly erected, it will not twist or warp, and will last a long time, even in our humidity.

I live in New Zealand so can't really provide any specific construction details for your region.
However, I used to work in the Forest Research Institute and later managed a timber processing company.
Local building regulations will dictate which types of timber you will be required to use and the dimensions needed for your purposes. So a local timber yard this is where your first line of enquiry should be.
Treatment and seasoning.
If the timber you are thinking of using is not durable (able to withstand the insect and/or fungal attacks of it's situation), it would need to be preservatively treated. The preservation process will be dictated by your local council or building authority.
Seasoning - This refers to the process of drying the timber. In some instances the timber will only need to be air-dried but in others, it may need to be kiln-dried. The difference between these two types of drying (in simple terms) is the final moisture content of the timber.
Kiln-dried seasoning is done in a kiln (controlled conditions) and produces an intended moisture content below about 12% in pine.
Air-dried timber is stacked in the open (usually) and relies on the elements to facilitate the drying and produces a moisture content range of between 18% and 25%.
in some cases the treatment process may require dry (usually air-dried) timber before it is preservative treated. It will then be wet again and need drying again to be at a specified moisture content for internal use.
After seasoning, the timber is more dimensionally stable and the resulting moisture content will be selected to suit the in-use situation.
A climate-controlled house would most probably require a moisture content of about 12% (kiln-dried) whilst a barn might only require 20% (air-dried).

You mentioned that the final product will be in an exposed situation. If this is the case, the timber may only need to be air-dried after the preservation process (if needed at all). However, air-drying takes time (months) whereas kiln-drying takes days but is more expensive.
Talking to a local builder should get you some pointers as to what you need to look for.

Hi,

I can put you in touch with a company that produces very hard timber - useful for structural work. Can we do a supply contract with your company?

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Have a great holiday season.

Viswa

I think you should allow trees to grow into the next century.

Use Bamboo --- we can supply any amount-- will enable optimum use of strength at 20% cost.

Please visit www.safebuildcheapbuild.com,www.assambambooworld.com

6x10,8x12,10x14 inch cross sections? Like Sal wood Rail Sleepers of last century!

No liquid will ever penetrate these heavies-- nor will the % moisture be stable for years

If you're going to use dressed lumber, make sure it is Kiln Dried and has a Moisture Content 15% or less.

Wood preservatives will make the shrinkage and expansion problems much worse and will induce checking.

Depending on the wood species and grade selected, those large rough sawn timbers are special order and require several years of curing in a wood yard before they are acceptable for use. You do not want to use green wood. Specify to the timber supplier that you want kiln dry timber (KD15).....of course you will pay a premium for it!

Check with the National Design Specification for Wood Construction (NDS) and the accompanying Commentary for details......visit the American Wood Council website for more details at:

www.awc.org

When all else fails, you can calculate the amount of linear shrinkage in a given timber (initial MC at erection time - the "TARGET" environmental-exposure MC for your region), then calculate the necessary force(s) to obtain that linear displacement along the timber length...then apply said forces in your moment connection design.

Are you a Structural Engineer?

You know, you can also use laminated timbers if they're exposed to view. Just make sure that the manufacturer uses exterior grade adhesives and that the glue-lams receive an exterior grade warranted protective clear coat....

I'm a high end home builder, and architects usually shy away from letting us use regular pressure treated wood that's exposed, unless it's underwater and unseen. It is usually made from southern yellow pine, a wood that had no value because it checked and cracked during drying, until they found it was soft enough to accept the cuprious oxide (PT) to a decent depth into the wood.

I would suggest a kiln dried (to 19%) mahogany, cedar, white oak (not red for exterior), or for more expensive options, Teak or Ipe. Or you could make the sturcture out of steel and clad with above for the timber look, then no connectors have to show. Drying to a lower moisture content would only cause swelling over time outdoors. And there are clear treatments that can preserve these woods even further than their natural capability, such as a West (r) Epoxy system.

Or you could do a mortise and tennon beam connections if the engineers give it their blessing, and avoid all steel all together, Use S.S. fasteners wherever possible.

Alan

Many of the local timber saw mills, in logging areas, saw out and kiln dry this type of lumber. Treated wood is entirely different than wood set aside for structural uses. Wood like Greenheart is kept underwater so it will not check but it is fender timber used as ship rub rails under bridges and almost entirely impermiable to marine borers.

There are also commercial bridge building timber suppliers, who will supply you cut to order, with mortise and tenons already cut to blueprint dimensions. These timbers can be treated as you wish, after cutting as designed.

While your letter is guarded in the writing, wood sections have been used the way you describe for centuries, after initial drying the little expansion and contraction does not affect the internal cellular structure of the wood, only the outside cells, provided it is dried properly. Any treatment should be done under pressure to force the treatment chemicals into the wood. It will still only penetrates the first 10% +/- of the surface wood.

Steel can also be alloyed to retard the corrosion of the saltwater environment. It all depends on how much money you are willing to pay for materials. US Steel has had, for nearly half a century, an alloy that the rust it develops, is the protective coating that replaces painting. However, it is rust in color and not aesthetically pleasing, so rarely used.

Another method you should consider is using pressure treated engineered lumber (see apawood.com or google "Anthony Forest Products" for more information)

I built a small but long 25' bridge for a stream in my back yard. I used pressure treated glulams for the main trusses and put the decking across them. I use it for a garden tractor and trailer. Fully loaded they do not produce any flex in the bridge even when measured with a tape measure. Only problem I had with them was my helpers got called away for a structure fire and I had to use come-a-longs and other mechanical devices to build it single handed, but I got it done in an afternoon. Not bad for an old geezer!

Treated Glulams are available in many sizes and lengths. I got mine from a local lumber distributor in central NJ.

Good Luck, Old Salt

http://www.accoya.com/

Lotsa $$$, but dimensionally stable. Not for the faint of heart.

Hi there Malarkkee...is your name a judgement of the worth of your question?

As may be, but I will give you the benefit of the doubt!

We have heard of some very interesting woods from respondents around the planet.

Many commercial buildings here in the Northeast of NA were built using Hemlock, Yellow Pine or Douglas Fir timbers. I have dismantled a number of these buildings, including Cotton Mill primary structures, Port warehouses and so on. The most rot resistant were framed in Hemlock.

I have built a few buildings and other structures using both Eastern and Western Hemlock. Transport Canada specifies this stuff for wharves treated with CopperSalt preservative They both have straight grain with almost no checking or twist. It is one of the stronger softwoods and is commonly used without preservative where the law forbids toxic poisons in the environment. Your connections sound appropriate for smaller structures although thru-bolts always trump lag screws. The traditional fastener which transfer load best of all would be "ring-bolts", but it does not sound like your structures will need these...special tools required...one of those lost craft things.

Malarrrrkee,

Although your question and follow-up posts supply some information, you leave a lot uncertain. My answer is based on the following assumptions:

• You are building in the USA.
• You are talking about the typical commercially available types of preservative treatment used in lumber sold here.
• You are concerned with dimensional stability as the wet treated wood dries after erection of the structure.

The wood treatment process is to kiln dry the lumber (up to an 8" section thickness) then put it in a vessel where a partial vacuum is drawn then an aqueous solution of the preservative is pumped in, and finally to pressurize this vessel to help force the solution into the open pores of the lumber. The resulting lumber is very wet and usually sold in that form. Any drying is only because it is exposed to the air on the edges of the large shipping bundles (called bunks).

Then, when this lumber reaches the job site it is exposed to air and, unless kept from bowing or bending, it will deform to some greater or lesser extend. This is bowing, twisting, checking or cracking--all because the lumber has two different rates of shrinkage as it dries--across the grain and in the direction of the grain. Unless the lumber is quarter-sawn or otherwise cut so the grain rings are running side-to side, there will be problems. Timbers usually are cut with the center of the trunk or limb running down the length, so cracking and non-flat sides are common and the other deformations occur if the original tree was not straight and the cut is not straight with it.

However, you can request the lumber yard to sell you pressure-treated lumber that has been kiln-dried after treatment, abbreviated as "KDAT" in the trade. Very few vendors normally stock this because the cost is higher and the market tends to sell only at the lowest price. But they can get it if you give them some lead time and your exact requirements. During the kiln-drying process, either before or aftr treatment, the lumber is racked in such a way that there is minimal chance for the shrinkage to produce excessive warping, cupping, twisting, bowing, etc., and before shipping it to you all the pieces that have these problems can be sorted out.

As others have pointed out, you would want to specify the maximum (and possibly minimum) moisture level in the wood as shipped. By all means, work with a knowledgeable salesman/vendor for this. Very few of the "big box" type of building supply stores have anyone who can do it. You will find people out there who know what you are wanting and can get it for you.

Now, a word about the types of chemicals used in pressure treatment. Creosote and similar petroleum-based materials were widely used at one time but have significant problems with toxicity. CCA (chromated copper arsenate) was used for a long time but is now outlawed in most applications because of environmental concerns about the stability and toxicity (definitely true when burned). ACQ (ammoniacal copper quaternary)and a couple of similar chemicals are typically the treated lumber commonly available, but they are quite acidic and corrode any unprotected fastener quickly (how about plain 16-penny nails rusting through in less than one year; so hot-dipped galvanized, phosphor-bronze, or stainless steel have all become the only acceptable ones). Borate provides excellent rot, fungus, borer and fire resistance without the corrosion of ACQ, but cannot be used if the lumber is exposed to rain or in the ground, because it leaches out in those environments.

Hope all this helps. Many posts have spoken of lumber/timber types that are inherently rot resistant, but with some concerns for availability or sustainability of forest production. They should not be ruled out. However, if treated lumber is chosen, then KDAT with ACQ if exposed to the weather or KDAT with Borate if protected from the weather (such as by overhangs, etc.) Talk this over with your architect or structural engineer (or are you this person?).

JMueller, occasional residential builder and many other things.

Good info, GA.