Designing a small barn. Where to begin??

[ckprivette]

Hey y'all. I'm brand new to the forum. I've been reading many threads and love the wealth of info on here!

I'm in the beginning stages (thinking, dreaming, planning) of building a basic (I think) timber frame barn. Trouble is, I'm a builder- not an engineer, and I kinda want this thing to stand for a while after I build it. I need some help with the designing aspect of my little project. Things like maximum spans, suggested timber sizes, post spacing, etc.

Where do I begin? Thanks in advance for the help!

chris

[jamesamd]

Here
https://forestryforum.com/board/index.php?action=toolbox

Jim

[Mad Professor]

A lot will depend on what sort of wood you are using, and loads.

Hardwoods vs softwoods?

And what kind of which?

[ckprivette]

okay, here's what I'm hoping to do.

I plan to use @12" diameter locust for the posts, and poplar for everything else. I have access to much poplar, so I can cut whatever size timbers are required.

I'm thinking a 12'X36' barn. I was hoping I could get by with post spacing of 12' all around. I'm planning to store only hay overhead, so relatively low weight. I plan to add side sheds in the future.  Would 6"x10" poplar span the 12' okay?

thank you,

chris

[witterbound]

Don't know about your hay, but my hay is heavy.

[Jim_Rogers]

I can't find any design strength values for poplar in my NDS book. So I can't tell you if it will work as a beam or not.

I use 60 lbs per sqft for most hay lofts in barns.

Maybe Dr. Gene can post some info that will help us with figuring the Fb, Fv and E values of poplar. You'll probably have to be a little more specific about what or which kind of poplar. I can see yellow poplar in my book but only to be used for 2x4s and such things. Thickest listing is 4" thick.

Jim Rogers

[Thehardway]

In the Mid-Atlantic states Tulip Poplar was often used for building barns as both beams and as siding.  It is not good as a post as it has no rot resistance in ground contact and often develops deep checks.  Their have been a lot of studies on the potential for use of poplar as a pine alternative for conventional framing.  Many of its characteristics are similar. Slightly lower in bending strength but likely higher in other areas depending on quality and growth rate of the trees harvested.

Following copied from Wood Database:

Average Dried Weight: 29 lbs/ft3 (455 kg/m3)

Specific Gravity (Basic, 12% MC): .40, .46

Janka Hardness: 540 lbf (2,400 N)

Modulus of Rupture: 10,100 lbf/in2 (69.7 MPa)

Elastic Modulus: 1,580,000 lbf/in2 (10.90 GPa)

Crushing Strength: 5,540 lbf/in2 (38.2 MPa)

Shrinkage: Radial: 4.6%, Tangential: 8.2%, Volumetric: 12.7%, T/R Ratio: 1.8

Hopefully this will help for strength calcs.

Make sure your locust is black locust.   Honey or Thorny Locust is not much good.

As far as where to begin,   I would start with a sketch of your idea,  either with paper and pencil or if you are more technically saavy, maybe something in sketchup.  Put that up on the forum and let us take a gander. 

[ckprivette]

Great! I will do that. thanks, fellers!

chris

[Jim_Rogers]

In the Mid-Atlantic states Tulip Poplar was often used for building barns as both beams and as siding.  It is not good as a post as it has no rot resistance in ground contact and often develops deep checks.  Their have been a lot of studies on the potential for use of poplar as a pine alternative for conventional framing.  Many of its characteristics are similar. Slightly lower in bending strength but likely higher in other areas depending on quality and growth rate of the trees harvested.

Following copied from Wood Database:

Average Dried Weight: 29 lbs/ft3 (455 kg/m3)

Specific Gravity (Basic, 12% MC): .40, .46

Janka Hardness: 540 lbf (2,400 N)

Modulus of Rupture: 10,100 lbf/in2 (69.7 MPa)

Elastic Modulus: 1,580,000 lbf/in2 (10.90 GPa)

Crushing Strength: 5,540 lbf/in2 (38.2 MPa)

Shrinkage: Radial: 4.6%, Tangential: 8.2%, Volumetric: 12.7%, T/R Ratio: 1.8

Hopefully this will help for strength calcs.

Make sure your locust is black locust.   Honey or Thorny Locust is not much good.

As far as where to begin,   I would start with a sketch of your idea,  either with paper and pencil or if you are more technically saavy, maybe something in sketchup.  Put that up on the forum and let us take a gander.

Thanks for that info.
But it only gives us the E we needed.
We also need the Fb, Fv values.
How do we use the above information to get these values? I don't know how to convert them.

Can anyone tell me how?

Jim Rogers

[Thehardway]

Ok, here are the values based on small clear unseasoned green specimen 2"X2" in cross section.  Bending span 28",  according to US Forest Service ytable in Wood Lumber & Timbers, Phillips A. Hayward, 1930 ed.

Green weight per cu.f.t 38lb.
Air Dry weight per cu.ft. 28lb.
Kiln dry weight per cu.ft. 27lb.

Bending strength (modulus of rupture) 5,570 lb.sq.in. Bending strength relative % to oak 64

Strength in compression parallel to grain 2,550  lb.sq.in. relative % to oak 72

Strength in compression perpendicular to grain 310 lb.sq.in. relative % to oak 43

Modulus of elasticity in bending 1,207  lb.sq.in. relative % to oak 92

Shearing strength parallel to grain 787  lb.sq.in. relative % to oak 60


In all of these white oak is considered 100% for comparison.

There are some serious discrepancies here between these ratings and the previous from Wood Database which I cannot account for.

Here are the numbers the same reference gives for Northern White Pine which posts almost the same weight numbers.   As you can see they are pretty close with poplar out performing white pine slightly in most categories.


Bending strength (modulus of rupture) 5,310 lb.sq.in. Bending strength relative % to oak 61

Strength in compression parallel to grain 2,720  lb.sq.in. relative % to oak 77

Strength in compression perpendicular to grain 314 lb.sq.in. relative % to oak 43

Modulus of elasticity in bending 1,073  lb.sq.in. relative % to oak 82

Shearing strength parallel to grain 644  lb.sq.in. relative % to oak 49


For general purpose in barn building, I feel you could size timbers the same is you would if you were using White Pine.

Does this help?

[Jim_Rogers]

Yes.
Thank you.

[Jim_Rogers]

Would 6"x10" poplar span the 12' okay?

I took a few minutes and ran some numbers through the online beam calculator and as a floor joist it would work to support a 60 lbs floor load spaced 2' on center.

But as a tie beam holding up the floor joists it will not.

See attached pdf drawing.

Jim Rogers

[D L Bahler]

The guys here are a wonderful resource for things like figuring the engineering out behind something, crunching the numbers, etc.

Sometimes I think Jim just patrols the internet, looking for people to help....

Before you get too deep into all that, though, you really need to have a pretty solid idea of what you want.

I am a believer that the design of a building shouldn't follow the numbers, the numbers should follow the design. But there are of course boundaries to good design.

I'd suggest you look at historical examples and see what they did, and that will give you a good place to start, you'll figure out the boundaries you are able to work within. Then you can start punching numbers, if you want. (Me, I rarely punch numbers. I just stay within the boundaries I learned, which I know are WELL within the limits of engineering)

[Thehardway]

Nice work Jim.  I like your drawing.

Would some oversize knee braces to reduce unsupported span help him out any?  The barns I saw built with yellow poplar typically used 10"X10" or larger for connecting tie timbers placed on 10 X10 Oak posts and were 3 bays wide X 4 bents long (30'W X 40'L).

One of them we converted to a dairy barn and needed more space for stanchions so we replaced the wood posts with 4" steel pipe.  I believe it had a 10' span between posts.  Sometimes they used a full log with the top side hewn or sawn flat to accept joists and double planked floor.

Chris,

D.L. makes some good points.  Form should follow function. Those 30'X40' three bay barns I mention were a traditional tried and true design.  They were based on the 3,4,5 rule (golden mean) that goes all the way back to the Greeks and Romans.  They were proven over hundreds of years and then again proven by farmers not only for functional use but for expansion, maintenance, durability and repair.  Some were modified for special use considerations or added on to as needs grew but the basic core was there. Shed style additions were common.

Make sure you know what the basic function of the building will be and then think some more about the future.  You will have a lot of time and effort in this when complete and you want as few Wish I had... thoughts as possible afterwards.

What kind of ceiling/clearance, floor, and roof heights do you need, how much hay do you plan to store, how do you plan to get your hay up and down, what kind of doors do you plan to use and where are the locations, will knee braces cause obstruction issues, what style bents do you plan to use etc. etc. Do you want a gable roof or a gambrel style? What eave height are you planning on, is it sufficient for future add on sheds? You get the general idea of where we are going.

[Jim_Rogers]

Normally most engineers don't consider braces as "load bearing" they are in the frame to create "stiffness" that the frame can't rock from side to side when the wind blows on the walls.

However, if you don't tell anyone, my engineer does consider one of the two in the pair. So the span is reduced by the length of one brace. This works, at times to get the beam size a little smaller.

Jim Rogers

[ckprivette]

Okay, fellers, here are some pictures for y'all to look at and critique. (Be gentle, I'm no architect.  :D) Actually I welcome all suggestions and corrections. Everything is not to exact scale, but hopefully you can get an idea of what I'm thinking about.

What's not included in the drawings is my plan to add side sheds in the future, but I figure that won't be too troublesome.
Also, ideally, I'd like to add more room in the loft by increasing the "upstairs" wall height to 3-4'. I'd love your suggestions for pulling that off, but if it's going to be too much trouble for me to build I'll probably just stick to what is sketched.

Heaps o' thanks, y'all!

chris



 



 
 

 




 

[ckprivette]

I'm sorry, those pictures are hard to see. I hope you can enlarge them.
chris

[D L Bahler]

go to googl.ch, type in 'kniestock' then click 'bilder'
that should give you some good pictures of some framing methods for knee walls

By increasing the upper story to a 4 foot knee wall height above the tie, you have to rethink the whole roof framing. otherwise, the tie is too far away from the rafter connection to resist the thrust and the frame might fail here.

Other cultures came up with solutions to this idea. In Switzerland, knee walls are very common on farmhouses that needed just a little bit more space in the upper level, but not a whole additional story.
If you have a truss roof, you have to come up with a way of tying the thrust down into the tie beam, so it won't push out on the plate and the posts above the tie.

[Thehardway]

Chris,

The drawings give us a good idea of what you are trying to accomplish, but, to put it gently, they are lacking in TF joinery fundamentals.  The best recommendation I can give is to do some reading.  Books by Sobon, Chappell and Benson will give you the basics you need to proceed.  Also check out some historical TF trusses.  They are available on the TFGuild website.

Now to be more blunt.  The location of the plates and use of joints over the posts are a real issue in my opinion. Additionally, the mortice and tenon size is not correctly proportioned and the pegs are not correctly sized or positioned.

The Joint you show at the rafter apex is also incorrect and the size of the rafters is likely inadequate for a principle rafter with purlin design like you show.

It appears to me that you are combining elements of post and beam construction with those of timberframing. Although many use the terms interchangeably, they are in reality two separate disciplines and you will get very confused trying to mix them.  Post and Beam construction relies on through bolted steel plates for joinery and strength and load transfer is much different.  It typically is a very vertical style construction using central posts and ridgebeam from which the rafters hang.  This design limits the thrust at the eave.

Timberframe is broken into two primary schools of thought.  Traditional Timberframe strives to eliminate high central posts and builds in a more layered horizontal fashion using short posts at the eave tied into long, continuous sills and plates,  with each layer tied and braced to form a rigid "frame".  Modern Timberframing uses a series of bents (vertical frame assemblies typically using rafter or trusses) in modular fashion which are raised fully assembled and joined together using tenoned girts inserted into mortices in the sides of the posts at time of raising.

Girts should not be used as plates (this is what you have done) nor should they be used to control rafter thrust. This would be the function of a tiebeam and a top plate.

Reading books by Sobon and Chappell will help you to see and understand these design principles and the terms which accompany them.

I will try to do a couple quick sketches later today and post with some ideas which may work better for you.

[ckprivette]

TheHardway,
you have correctly identified my ignorance.  ;D Thanks for the tips and the coming sketches. I will take your advice and rethink my thinking.

I'm okay using elements of post and beam in the structure if that would be the easiest solution. I'm just trying to find the simplest way to get where I want to go. i.e. fewest and simplest joints, etc. Of course, above all I want the shed to be sound and to last, so I will make it as complicated as necessary to accomplish this. 

thanks again,
chris

[Thehardway]

Chris,

I have a suggestion.  There is a plan for a 12'WX16'L timberframe shed which has kneewalls for extra attic storage. by adding length to it (which is very easy) it would make the 12'X36' that you need.  It is called the Sobon Shed and the cut list, designing, joinery etc. info is contained in Jack Sobon's book titled "Timber Frame Construction"  It is available in e book form for $9.99.  It would be good money spent and will give you all of the knowledge you need to move forward.  There are also numerous folks here on the FF who have built this  exact shed and can give you specific guidance should you run into a snag or have questions on things not clearly explained to your satisfaction in the book like this little video Jim did https://www.youtube.com/watch?v=Ri7RoHmaZoA

You will notice the video points out the top plate/rafter joint which shows clearly what I was trying to tell you in my criticism of your drawing. 

If you really want to do your own design, there is nothing stopping you, I'm just thinking ther might be no reason to redesign the wheel here when the Sobon Shed is so close to what you have expressed a desire for and plans/support are so readily accessible.

Let us know what you think.  Also be aware that things like door locations etc. can easily be tweaked to meet your needs.

As for using steel plates, we try to avoid it unless there is a specific reason to go there (ie. inspector demands it, specific point loads or no other options available) because they add cost, complexity and have proven not to last as long as all wooden joinery over the test of time.  Steel or iron tends to sweat as temperature changes and collect moisture which causes rust and more moisture to be collected and this deteriorates both the wood and the fastener.  In old buildings where steel or iron fasteners were used, "ironically" (pun intended)  they performed inferior to their all wood joinery counterparts in terms of longevity.  Additionally, Steel plates/bolts expand and contract at a different rate than wood.  As the wood shrinks and swells with climatic change, the steel fasteners will get loose or can crush the wood fibers causing premature failure.   There are a few instances where things like iron king post rods for supporting a tiebeam or using iron rod to control eave thrust have been done with success and also some cases for use of concealed steel fasteners where situations did not permit adequate wood material for a good wood joint.  This is rare.

I think we can keep you free of that issue.

[ckprivette]

Hardway,
I'm all for purchasing a plan- like I said I'm no architect.  I'm a builder, and I actually prefer gong from a plan, that designing it myself. However, judging from the video, I'd need to make some adjustments to this plan, and I'm wondering if that would be possible. Please tell me what you think.

What I'm wanting to build is more of an open pole shed than a barn. It will not have siding or doors on the bottom, but rather will be open all around for me to walk through, and also drive through with my tractor, and for storage of tractor attachments- bushhog, baler, etc. Therefore what I need all around is 12' between all posts- sides and ends. On the video it looks like there is a set of additional posts between the corner posts on the front. Also, the side posts in the video are @8' apart, and I'd like 12', which would dictate larger plates and girts, right? And, there are some girts between the side posts that I'd need to raise considerably, or, ideally, leave out altogether. Given all this, is this still a plan I should start with, or is there another out there that would need fewer changes? Many board feet of thanks!! chris
   

[Thehardway]

Chris,

I believe you could adapt the plans found here to your use by adding another bay and shortening the span.
https://forestryforum.com/board/index.php/topic,55956.msg809758.html#msg809758

or going the other direction making this plan slightly larger

https://forestryforum.com/board/index.php/topic,49542.msg715914.html#msg715914

There are other plans in the Depository, at the top of the page that you might want to check out as well.

There are numerous sources of plans available for sale on the web or from TF designers for fee ranging from $50 to several hundred depending on the level of detail and engineering you desire. a

I prefer teaching a man to fish rather than giving him a fish but some guys just don't make good fishermen and are better off as gardeners or hunters and paying for there occasional fish ;D


Apart from the braces, the intermediate side wall members of most Timberframes are their primarily for the attachment of siding, doors, windows, etc. and can be relocated, moved or deleted. In my opinion the Sobon shed could be built without sills and sidewalls if the posts were subtantially anchored and the bracing post/plate and post/tiebeam braces were left in place.  The 8' post spacing can be lengthened as long as the plate and joists and tiebeams are also sized for the load of the increased span.  I believe he covers this in the book but I don't have it in front of me at the moment.

No matter which way you go, the book is a good idea to read.

[ckprivette]

Help! Help! my line is in the water but I don't know what to do next. Do I turn this crank thing on the pole? and which way?!! how deep in the water should my rod tip be? Why would a fish bite this line? should there be something tied to the end of to to entice them. Oh my am I hungry.

Seriously, I plan to learn much from this whole process (i already have) But, teach me more, brother! thanks for the plans. I think one of them may work- if I can figure out how to download it. Sketchup is new to me, but I'm studying my fishing manual. i should have a stringerful by sundown.
chris

[Thehardway]

That's the attitude my friend! We are all learning... everyday.  I have plenty of days when my stringer is empty...  how far south of the VA line are you in NC?  We may almost be fishing in the same pond.