Design questions for a new barn

[MHineman]

  Only 2 horses now, but used to have more.  The barn was expanded with a lean-to along each 30' side.  The 13' or so up to the eaves was planned in so the lean-to would have a 4/12 pitch.  Part of each lean-to was used for stalls, part for a buggy, and part for tools.

  Now the loft holds lumber as well as hay.

  The aisleway always made taking care of the horses in bad weather a lot more resonable. The space with 10' wide doors allowed more ventilation too when needed.  I would not want to feed, water, and groom the horses without it.

  I figure 150 to 180 days each winter feeding hay.  Depending on size of animal and quality of hay, from 1/3 to 1 bale per horse per day.  It doesn't take many horses to use up 400 bales.

[Jim_Rogers]

Ok, so I put some hay into a 12x30 frame with a 10/12 roof pitch and a 3' knee wall.

And this is what I got:



There is barely a walkway to walk down the middle but if the barn loft was fully loaded with 15x20x36" bales of hay stacked like I have them stacked you get 11 per side or 22 per row.

There are 10 rows in 30' so that 220 bales x 75 lbs per bale or 16,500 pounds.
Next there is 12' x 30' or 360 sqft of loft.
16,500 divided by 360 = 45.83 or 46 lbs per sqft. "live load"
Now we add the dead load which is the floor itself. Average is 10 lbs per square ft for average dead load. So now we're at 56 lbs per square foot.

If these numbers are correct, and someone please "run the numbers" for me and make sure I'm doing it right. And post if I'm wrong. We now know what load the floor joist has to hold up under the area of the deck that it will hold up.

Now we can size and locate the floor joist to see what size it needs to be.

On the forum is the red tool box. In it is DonP's calculators. We select the second one down on the list for beam and column calculator.

When that list opens we then select second calculator down the list for uniformed loaded beam and pull down values.

When this opens we see we need to figure the load on one beam/joist.

Let's say we have a floor joist that is going to be spaced 2' on center (oc for short) so that means the floor joist is going to hold up a strip of floor 2' wide and the distance from one tie beam to another. The bents are 12' spacing less the tie beam so that's 11' 4" or 136". 136 x 24 = 3264---3264/144 = 22.67 or 23 sq ft. -- 23 sq ft x 56 lbs per sq ft = 1288 lbs.

So one floor joist in a fully loaded hay loft is going to hold up 1288 lbs.

Let's enter that into the calculator on the first line.
As this calculator asks also for the dead load, which we have already figured into the total, we'll just leave that line at zero.
Next we enter the span in inches which we figured above at 136. And then need to pick a size of a floor joist. Lets try a regular timber like a 4x6 and see if that will work.

So we enter 4 and then 6. Next we need to use the pull down menu and select the correct type of wood.

Opening the menu with the pull down arrow we see that there are two lines for each for each type of wood in each grade. One says B+S and the other says P+T. What these mean is the B+S is for "Beams and Stringers" and the P+T are for "Posts and Timbers". Which one do we use?
Well you have to understand that the guys who figured out these values assume that if the timber is taller then it is wide you're going to use it as a beam. The set it up so that any timber that is more than 2" taller then it is wide is going to be used as a "Beam or Stringer". And timber that is the same size both ways, like a 8x8 is most likely going to be used as a post. So any thing like a 4x6 is in the P+T category.
So we use that one.
I selected eastern white pine grade #2 P+T and the clicked "Show results"

This tested the floor joist to see if it would be ok. The results say it fails.  So this size floor joist is not going to work.

Lets move it up to a 4x7 and test again. Just change th 6 to a 7 and hit show results again. But select eastern white pine grade #2 and B+S.

It still fails. But not as bad.

What will we do next?

We can continue increasing the size of the timber until it passes, that is one solution.

We can change the type of wood to a stronger type, that is another solution.

We can put the floor joists closer together so that the load is reduced on each one, that is also a solution.

Remember we have to size the floor joist first to hold up the floor.
Then we have to size the tie beam to hold up all the floor joists.
Then we have to size the posts to hold up all the tie beam load.

Again a long way around to answer the question, "Can I get away with a 6x6 for a post?"

I still don't know yet.

More later.....

Jim Rogers

[Jim_Rogers]

What solution should we choose?

To decide let's look at a beam sizing standard:



One rule in this drawing, says that the floor joist should be 5/6's of the size of the tie beam depth.

So maybe we should figure the tie beam size first, then the floor joist.

The tie beam that I'd like to size is the one that will hold the most weight. Then make all the others the same size to make everything easier. What I mean is we don't want four different size tie beam for for bents.

Which tie beam should we size.

Bent one and four have floor only on one side.

Bent three has floor on both sides but one side is shorter then the other.

Bent two seems to be the one to use.

Ok, so bent spacing is 12' from bent to bent. That means the floor being held up by tie beam in bent two is 6' on one side and 6' on the other so 12' overall.

The building is 12' wide, we could just say 12' x 12' but the tie beam is shorter then 12' because it connects to two posts. Let's say each post, for now, is an 8x8. So the tie beam is now 144"-16"= 128" which is 10'8". So 10'8" x 12' = 128 sqft. 128sqft x 56 lbs = 7168 lbs being held up by the tie beam.

Lets go back to DonP's calculator and see what size tie beam will work.

Opening the same calculator we enter in the weight of 7168. And the span of 128, and then we need to pick a size of a tie beam. Well if we're going with a 8x8 post then we want the tie beam to be the same width. So 8" for width. Next let's try 10" for depth. So we enter these values.

Now knowing that the 10" depth tie beam puts us in the P+T category we'll select eastern white pine grade #2 P+T in the pull down menu.

And press/click "show results"....

We see that this size tie beam fails in bending.

Ok, so let's change the depth to the next size bigger, enter 12" and change the value to B+S for eastern white pine grade #2. And we see that this size tie beam also fails.

So we need a bigger beam, again.

Let's go to the next size up. Well softwood are cut on even inches so that make the next size a 8x14

And as this size is still in the B+S category we just change the 12 to 14 and click show results again.

Now the beam passes.

We know know that the tie beam has to be a 8x14 grade #2 in eastern white pine.

Ok so if that is the size of the tie beam. And the standard says the floor joist can only be 5/6's of the depth of the tie beam. 5/6's of 14" is 11.6" around 11 5/8.

So we can increase the size of the floor joist up to 11 5/8" until it passes.

Back to DonP's calculator.

Re-enter the weight amount from the floor joist of 1288. Change the span back to 136 and enter the floor joist size of, let's say 4x8 and click "show results".

And the floor joist passes on all three test.

So we now know the size of the floor joists which are 4x8 eastern white pine grade #2 or better.

And the size of the tie beam which is 8x14 eastern white pine grade #2 and better.

Next we will see how the post will be sized.

Jim Rogers

[jPell]

Good stuff, Jim. One question, the weight of the floor joists... is that somehow figured out as part of the dead load for the tie beams in the programing of the calculator or is it just not substantial enough to add into the equation? Or is that part of the 10 lb dead load average for a floor?

[Jim_Rogers]

I consider the floor joist and decking in the 10 lbs dead load. It maybe high but I'd rather have a floor that's stronger then it needs to be then one that is bouncy because it's too weak.

Jim Rogers

[jPell]

I see. And I'm with ya there on erring on the side of overkill.

I hope building this thing is half as much fun as it is figuring all this stuff out. Very interesting.

[Jim_Rogers]

128sqft x 56 lbs = 7168 lbs being held up by the tie beam.

Ok, so now lets look at the post that has to hold one one end of this tie beam.

If this post is only hold up one end then it is holding up 1/2 of 7168 or 3584 lbs.

We have to make sure there is enough bearing area of the tenon in the mortise on the tie beam to support this load.

What I'm looking at is this:



In the above drawing (called a wire frame drawing) we see the 8x8 post and the 8x14 tie beam. And the tie beam's tenon which is 2" off the reference face and then 2" thick and it is a through tenon, with a 1/2" housing. This type of tenon would be a standard tenon for such a barn using "square rule" joinery rules.

The highlighted "blue" area is the area that will bear on the post mortise and housing.

Now we have to look at the amount of square inches of this area.

The tenon is 2" wide x 7 1/2" long which equals 15 sq" (sq" mean square inches). Next the housing area is 1/2" x 8" or 4 more sq"; giving us a total of 19 sq".

The book with all the timber values, (NDS which stands for National Design Specification) says that the grade #2 eastern white pine timber can or should hold up 350 lbs per sq" perpendicular to the grain.
That is the bottom of the tenon in the tie beam.

So we take 19 sq" x 350 lbs and get 6650 lbs of support over that area.

Our load is 3584 that means that 6650 is greater then 3584, so we're ok with this size post.

Ok, so jPell's original question was, "can I get away with a 6x6 post instead?"

We're finally getting to figuring out his answer.

Now let's look at the new sizes of the tenon based on this size post.

If it was a 6x6 then we'd use a 1 1/2" tenon and it would be only 5" long, with a 1/2" housing 6" wide. So our new bearing area is now: 1.5x 5 = 7.5 and 1/2 x 6 or 3 totaling 10.5 sq".
10.5 sq" x 350 = 3675 lbs.

Our load was 3584. 3675 is greater then 3584 but only by 91 lbs.

Well are we ok?

Is this the only load on this 6x6 post?

No, it is not.

We haven't loaded the post with the roof load, yet.

Personally, knowing that we need to add the roof load, I wouldn't even consider trying to use a 6x6 post.

Of course we could go to a stronger type of wood for our posts.

But this may cost more to change to oak.

I don't know if jPell can get some oak or not. Or if he want to try to timber frame his first barn with oak, which is a much harder wood to work with or not.

I'll have to wait to see what he says after he reads my opinion stated here.

Jim Rogers

[witterbound]

Getting and moving  bales of hay up in the loft is going to be backbreaking work.  If you.ve got a tractor, I think you'd be much better off building an extra stall to store hay, because you can use the tractor to move the hay.  The idea of a hayloft is a romantic and appealing idea, but I don't think itis practical for most of us. 

[beenthere]

Jim
That was a very good explanation of figuring out the post size and presentation of the detail involved in why one needs to know the limitations of wood joints.
Certainly appreciate your efforts.

[Jim_Rogers]

Beenthere:
Thank you.

I know it seems like a long way to go to say a 6x6 may not work but that's the way I do it to try my best to figure it out.

Jim Rogers

[MHineman]

Getting and moving  bales of hay up in the loft is going to be backbreaking work.  If you.ve got a tractor, I think you'd be much better off building an extra stall to store hay, because you can use the tractor to move the hay.  The idea of a hayloft is a romantic and appealing idea, but I don't think itis practical for most of us.

  With a hay elevator, getting the hay into the loft is easy.  Besides, with the quantity of bales for this barn, it's good exercise even if you have to throw the bales through the loft door.  Not really any different than tailing lumber as far as effort.  If using small square bales, you still have to stack those bales even if at ground level.

  I've had hay in a loft and at surface level.  The hay in the loft stays fresh and palatable longer than hay at ground level.  I had skids on a concrete floor and the hay stacked on the skids.  This shed had no animals in it to add moisture and did not have any other moisture problems.  The first layer of hay had 75% or more of the hay with mold on the bottom.  The entire bale was not ruined, but for the other 2/3 of that first layer, the horses and cows did not like it much and wasted a lot of it.

  If the hay is stored on dirt or gravel, the spoilage problems are worse.  The space under the hay is a prime location for all type of undesired varmits when on dirt or gravel.  Everything from rats to ground hogs.

  Hay stored in a loft generally only has racoons and possums to deal with, but the hay at the surface does too.  A live trap with permanent removal (destroy them not relocate) usually solves that issue.

  This discussion about hay is only for small square bales which is what I think was in the original plan.  Unless you have enough animals to finish a round bale within a few days, you get too much hay wasted and square bales make better sense.

[Dave Shepard]

In reality, that 5.5" tenon is going to be 5.375" long, and if you taper it, the bearing surface is only going to be about 3" long, assuming an accurately cut mortise.

[jPell]

MHineman,
Those are pretty much my exact thoughts. I'm only 33 and definitely not afraid of a workout throwing hay. By the time I am old enough to lose interest, we'll end up getting an elevator.

Jim,
I have plenty of oak on my lot. However, like you mentioned, I'm not sure if I want to work with oak for my first project. 8x8 pine posts look to be the winner.

[Jim_Rogers]

Next we have to decide on which roof system jPell wants to have in his new barn.

He asked if he should go with a principal rafter and purlin roof system or a common rafter roof system.

Let's look at both.

Here is an example from the Historic Joinery series. It is a principal rafter with purlin roof system:



As this is a larger barn you can see that there are many purlins and the principal rafters are spaced only 6' apart.

Here is a common rafter roof system, from the same series of drawings:



Again this is a much wider barn and because of that they added a principal purlin plate under the rafters to hold them all up.

In jPell's case we wouldn't need a principal purlin support system as the span is only 12' wide.

In a previous post, I described that method of erecting a principal rafter with purlin system. And that it requires more joints to be cut. And more rigging hardware to be either rented or bought to make the assembly safe and go fast.

He asked if a 6x8 rafter would be big enough for his roof.

We'll we assume that he's going to use the same type of wood for his roof system which is eastern white pine, grade #2 for our values in our calculations.

Now, we have to figure the live load on one rafter, if he was going to use a common rafter roof system.

He has told us that the snow load for his area is 80-90 lbs per sqft. So we'll use 90 to make sure it's strong enough for his roof.

So, we now need to figure the area that one rafter will hold up. We need to start somewhere so let's just say he's going to use 2" tongue and v-groove roof decking over his rafters and under his metal roof. He may not but let's just say he will.

So 2" tongue and v-groove decking can span 4' because it has the tongue and groove. Let's use 4' spacing. So that means one rafter will hold up 2' on one side and 2' on the other so that's 4' over all.
Next, even though the rafters are at an angle the load is vertical. So that means the run of the rafter is the other dimension we need. As the span of the building is 12' the run of the rafter is 6'.
Now we can do some math. 6' x 4' = 24 sq' (sq' means square feet). 24 sq' x 90 lbs = 2160 lbs live load being held up by one rafter.

Next we have to add the dead load, which is the roof system itself. But this time we have to figure the load based on the slope of the roof.

A 6' run on a 10/12 roof system means the rise of the roof is 10" for every foot of run. That means the rise is (10x6=60") or 5'. Now that we have two lengths for our triangle we can figure the slope length.

Using the formula that A²+B²= C² we can figure the length of the roof slope if we re-write the formula and say C is the square roof of A² + B² like this:

C= sqroot of ((6x6)+(5x5)) or C= sqroot of (36+25), or C= sqroot of 61, then C=7.81 ft. C is the rafter length from the outside of the building to the ridge.

Next we have to add to C the over hang length. C= 7.81 + 1 or 8.81 rounding up we say 9'.
So the rafter is 9' long.
The area it holds up is 4' x 9' so we may have to add some to the live load. Because I forgot to add the overhang earlier.

If we use the standard estimated roof dead load of 10 lbs per sq' we'd have a dead load of 360 lbs. (4x9=36x10=360).

Adjusting our live load again to add the overhang we now have 4' x 7' or 28 sq' x 90 or 2520 live load and 360 lbs dead load.

As we now have our load values we can again go to DonP's calculator and opening the same one we used before we can add these load values into his calculator.

In the first box we enter 2520, and the dead load as 360.
Next it asks for the span in inches. Well usually this is the un-supported span, but we'll make it 7' and in inches that's 84.
Next we enter our test rafter size of 6" x 8" and select the eastern white pine, grade #2 in P+T as it isn't larger then 2" as described before. And click on show results.

It passes on all three tests.

We now know that a 6x8 rafter spaced 4' oc will support the load.

Next we could see what sizes of rafter and roof purlins would be needed to do it with a rafter purlin roof system.

Jim Rogers

[dukndog]

Great job Jim!! Thanks for sharing your knowledge with us!!

Rich Miller

[grweldon]

Excellent methodical design illustration.  You are the man Jim!

[Jim_Rogers]

Thanks gr.....

We'll have to wait to hear back from jPell what he wants to do next....

Jim Rogers

[jPell]

Hey, Jim.

I think common rafters will work out just fine for this building. I'd love to do a rafter/purlin roof but I think it will just add too much time. As it is, I may be biting off more than I want to chew but I'm gonna give it hell.

[Jim_Rogers]

Josh:
Ok, thanks for deciding.

Next, are you going to put a deck over your rafters or are you going to attach some lumber above them just enough for the metal roofing?

We need to figure the correct span between the rafters if you're not going to use tongue and groove decking.

Jim Rogers

[jPell]

Not sure. I'd like to make T&G happen. 7/8 pine? Would green be a problem? Not sure if shrinkage would cause too much of a problem.

[Jim_Rogers]

On the shed I did last summer, for a client, we needed to figure the exact dead load fairly accurately.

So, what I did was I created a copy of his roof. He was going to use a 4x7 pine rafter, and over that a piece of 1x4 pine as a cleat for the metal roofing to secure to.
Then the metal roofing.

I did some research on the weights of metal roofing and as best as I could figure from what I found was that it weighed about 1 lbs per square foot.

Next I had to figure what the actual rafter and 1x4 would weigh for one square foot of area.

To do this I took the copy of his roof structure and in my cad program cut away all but one square foot of area.

The drawing then looked like this:



At the top you see a square that represents one square foot.
Next down is the metal roofing. It's a little thicker then actual metal roofing but it was just for visualization. Next down is the 1x4 pine cleat for attaching the roofing to, which was spaced at 2' oc. up the rafter
And lastly the pine 4x7 at a 10/12 roof slope.

After using the computer program to cut away all areas of the roof outside of this one square foot, I had the program generate a stock list of the wood materials. The program can calculate the weight of the materials if you have their base weight per bdft entered into the database.

It did this stock list for me:

LNo Part                 Pcs. W[ft] H[ft] L[ft]       Pr/unit [$USD] Cost [$USD]
1     overhang rafter 1      4"    6"    1'-8 5/8" 0.85                2.92
2      cleat                1      1"   4"     1'           0.75                0.25
Itemno.                 Pcs.[Pcs]   Volume[BF] Weight[lbs] Cost[$USD]
SPF-75                    1             0.33          1.0             0.25
SPF-85                    1             3.44          10.0            2.92
Total                        2             3.77          11.0            3.17

So my calculations proved that
1x4x 12" cleat stock bdft volume is .33 bdft x 2.92 lbs = .9636 lbs
4x6 rafter on 10/12 slope = 3.44 bdft x 2.92 lbs = 10.0448
Combined the dead load for one square foot of roof supporting lumber is 11.0084 or 11 lbs.
Metal roofing materials from my research is about 1 lbs. per sqft. This means that the dead load for one square foot of roof is about 12 lbs on a slope of 10/12.
The live load for the roof is 50 snow load for his area.
The total combined load of the sloping dead load of 12 lbs and the vertical live load of 50 lbs is 62 lbs per sqft.

If you're not going to the expense of sending out your lumber to be planed and tongue and grooved to create a deck over your rafters then we need to re-figure the roof rafter spacing.

A 1x4 may not be strong enough to span 4' from rafter to rafter. We may need to move the rafters closer together.

For the above example his snow load was 50 lbs and his rafters were 1'-9" apart with the 1x4 cleat. But they were only 4x6 rafters.

I think we decided after reviewing all this that we should up size the rafters and we did go with a 4x7 to insure we had rafters that were strong enough.

The whole reason why we do all of this is to completely understand all aspects of the frame.

Most people just want to know: "how much is it going to cost?"

We don't know until we figure out everything.

Decision have to be made, up front, and we have to stick to those decisions.
Changing one little thing later on effects all other things associated with that.

If we move the rafters closer together to reduce the span of the 1x4 cleat, then we maybe able to reduce the size of the rafter from a large 6x8 to something smaller and easier to handle and mill. Thus reducing costs.

jPell needs to decide on what he wants. Sometimes no decking means the bottom of the metal roofing is exposed to the loft area. I don't know for sure, as I don't have a building built like this here. But I thought I heard somewhere or some time that there can be condensation on the underside of metal roofing. And this may drip down onto the hay. Which may not be a good thing.

jPell has asked if 7/8" pine would be ok, even if it's green. And would the shrinkage cause a problem?

Back in either 03 or 04 I cut this pile of lumber and timbers for a client:



He cut his own frame and we helped him erect it.

Then he enclosed it. It was to hold up his solar panels and be somewhat of a shed or garage.

We returned a year later after it was done for a party and tour of his frame/shed/solar panel setup:



During that tour he told us that he took the boards I cut and planed them with his bench top planer, making them 3/4" thick or so.
And he ran them through his bench top router shaper table and cut tongue and grooves on this boards, without "sizing" them first. That is he didn't run them through a table saw to make them all the correct widths. He felt that my sawmill had produced accurate enough lumber that it didn't need that.
I'm not sure how dry any of this wood was when he put it up.

But when we returned for the tour, we saw this:



As you can see there are some large gaps between the boards he used for siding.

In more than one place.

Shrinkage is a factor you have to consider.

If you want to use green tongue and groove you'd going to get some shrinkage.
If it was me, I'd put some tar paper over the roof decking and then attach the metal roofing over that. This way if anything leaks, like the screws used to hold down the metal roofing. Or if you get some condensation on the bottom of the metal roofing, it will drip onto the tar paper and run down the roof. Instead of dripping into the hay loft.

I hope this has helped you to understand why decisions have to be made and how the effect everything else.

Jim Rogers

[jPell]

Ok, here's what I'm thinking (all input/comments/ideas/slaps to the back of the head if need be, are welcome).

Rafters, then 1x4 cleats, then the metal roof. As far as the condensation issues... with the loft being hay storage, there needs to be an enormous amount of ventilation which should help with that greatly. Having the cleats vs the T&G, I feel will also increase ventilation if we can keep from closing the eaves up too tight. Between the eaves and the gable vents and doors, the air should move through there pretty good. I'm just trying to think of it logically. Am I way off?

Josh

[routestep]

In my area of Virginia the engineer had to add in a roof load due to wind as well as snow. We get hurricanes or remanents of them. Not to many Northeasters.

[Rooster]

Ok, here's what I'm thinking (all input/comments/ideas/slaps to the back of the head if need be, are welcome).

Rafters, then 1x4 cleats, then the metal roof. As far as the condensation issues... with the loft being hay storage, there needs to be an enormous amount of ventilation which should help with that greatly. Having the cleats vs the T&G, I feel will also increase ventilation if we can keep from closing the eaves up too tight. Between the eaves and the gable vents and doors, the air should move through there pretty good. I'm just trying to think of it logically. Am I way off?

Josh

I'd go with common rafters 24 in. O.C. with using either 1x8 decking with an 1.5" gap, or just 2x4 cleats / roofing nailers 24" O.C.   There is also a product that is used with the steel ridge-cap that allows air to pass but not birds, bugs, or weather...it looks like a roll of black 3M padding.  I'll see if I can find the product name.

Rooster

[jPell]

Thanks, Rooster. Yeah, I know of the product you're talking about for the ridge vent. I'll be using that on this barn.