Interested in building a pole barn w/ rough cut lumber from a local saw mill. Question is where can I find data regarding the strength of framing timbers? What is stronger a commercailly available 2X6 or a rough cut 2X4 ?? The end sq in profile of commercial product is 8.25 sq in and the end sq in profile of rough cut is 8 sq in, pretty close to me. Anyone have any link ideas regarding framing timber strength ?? Thanks for the help !!
The term stonger is a relative term. Which direction are you applying the force to the wood. In general if you are using a piece of wood as a beam the 2 x 6 will carry more force. The weigh bearing ability is provided by the distance, 5.5 inches. Newer space beams for example use a piece of plywood between two 2x4s. The forces are carried by the top and bottom 2x4s in compression and expansion. The middle of the beam is only holding the top to the bottom.
This is similar to metal I beams.
Increasing the depth of a beam provides more strength per inch than increasing the width. A nominal 2x6 is stronger than a rough cut 2x4 if you are using them in the horizontal. If you are asking which is strong as a stud, they have a similar cross section and the stress on a stud is compression stress, (not shear or bending stress which apply to horizontal members).
Time to do some stress analysis if you are going to use rough cut lumber for things like floor joist and rafters.
$ wise you cannot beat local rough cut lumber. In upstate NY you'll typically pay $.25 - .35/board foot for clear pine. I picked up 1000 ft of 5/4, 10-14" wide this past winter, air dried it for 4 - 6 months and have used 80% already. Time to place another order.
I believe that building codes specify timbers and max spans for different applications. There even seems to be software that will design structures according to 'generic common denominator' codes. Contractors have tables that give requirements for all sorts of loadings etc. However, I believe that all these formal specs and stuff are keyed to not only finished but finished graded lumber. Ungraded lumber is much less expensive if it can be found.
I would inform myself about permit and code requirements. Around here any roofed structure greater than 100 sq ft needs a permit (except for an open sided pole shed used for firewood loophole). I know that only graded lumber is supposed to be used for residential structures and may be required for other structures as well. The idea of graded lumber is that it's supposed to guarantee an absence of flaws that would reduce weight-bearing capacity below specs. However, from what comes out of the stacks at our local building supply place, you have to wonder. Certainly the graders seems to be plagued by severe uncorrected astigmatism.
A person who did some inspection work for us and became a friend used ungraded lumber for roof sheaving on his house and got into an argument with the inspector about it. I think he finally got the work approved, but at a cost of a lot of aggravation. He worked as a building tech for a large firm of consulting engineers and probably knew more about building than the inspector. No matter, codes are codes as interpreted by the inspector. It's the nearest thing remaining of absolute monarchy in the west. A safe course is to ask what an inspector will approve before buying the materials. The last time I ran into our friend he seems to have given up on the aggrevation and became the building inspector for a different city so now he's the king.
Which is stronger, will depend on where the knots are (if any), what species you are comparing, and whether you are talking bending (MOE) strength, or ultimate (MOR) strength. If the 2x6 is a low-density wood but graded std. and btr, and the 2x4 is a clear, straight-grain high-density hardwood (white oak), the white oak will probably be stronger. The comments by Tom are very good. If its not graded, it may not be a question of which is stronger, but one of it not being graded by (or under the auspicies of)an inspection bureau. Once a builder (carpenter) cut off all the grading marks on one end of the joists (they were too long, and needed to be shortened) and lost to the inspector (ungraded material). In spite of what the material looks like, the grades are good and consistent. If machine graded, often the lumbert looks so bad appearance-wise, that a visual grade is applied just to cull out the poor lookers.
As Tom says, get the inspectors advance approval first.
Around here any agricultural building can use rough cut lumber, if fact a building permit for an ag building is not required.
If a non ag building exceeds 150 sq ft or is wired a building permit is required.
Talk to your local build inspector/code enforcement person. He'll be a wealth of info. You may be required to use graded lumber for studs, joists and rafter yet be able to use rough cut for sheeting the building, or you may be allowed to use 100% rough cut.
Yikes, I shorten lumber all the time and never thought about cutting off the marks. It's good to know that level of detail. I also had no idea that grading could be done by machine.
Our inspectors aren't quite so formal around here and everybody knows everybody personally. Still, getting nailed for no marks on the lumber is exactly the sort of thing that could happen even here if an inspector gets aggravated. Get one aggravated and chances are that a building will never be completed or it will cost so much that you'd wish it wasn't. I've always had great luck with both building and electrical inspectors myself. Theyíve even saved me a bunch by not only suggesting less costly designs but also pointing out the consequences of using lesser designs. Itís common enough for people to want to change the use of a structure and find that a different set of codes applies and a bunch of upgrade work is required. some people around here thought they were going to retire in their cottages. When they applied for occupancy permits they found that their cottages had to meet current residential standards. Inspectors know this kind of stuff that would never occur to most people. I talk to my inspector when I donít think I need a permit. Well, I guess itís easy for me to say, since I also fight fires along with my inspector.
Itís good to know about codes and that ag buildings may not need permits in many places but itís also good to keep the example of the cottages intended as retirement homes in mind.
You didn't specify what KIND of lumber. White Oak? Yellow Pine???
It makes a big difference.
Also, that lumber needs to be seasoned. It should be at least 1 year old.....the longer the better.
The old timers around these parts used to season it two years.
There are several old barns in my area that were built with lumber (usually white oak) that was from a woods on the farm that the barn was built. A man around here had made a portable saw mill and would set up in your woods and saw the lumber to your order. he died just a few years ago at the ripe old age of 97.
He could sit at your table, and tell you how many board feet was used on any barn you mentioned. (I must ad here, that there was no one left alive who could dispute him). He could also tell you about barns built in haste, and how much he'ed warned the farmer. You can then drive to the barn and see how crooked and twisted the timbers became within just 2 to 3 years from it's build date. the crooked barns are still standing, and whenevr someone trys to tear one down, it's evident how strong they are....but they are still crooked and twisted.