Another set of Pole Barn Questions

Tscott9330 · Feb 10, 2009

I have been reading a ton on pole barn construction, and have a few books on the way in the mail, but many of you have built these before, so I would like to ask a question.

I am in the process of designing a 40' by 60' pole barn as a shop. I am investigating the possibility of using attic trusses to allow for a room over the shop. I have not seen any pole barn type buildings with attic trusses. Is there a reason for this?

Here are some PDF's of my current plan.
View attachment Shop side view 40' x 60' attic truss Model (1).pdf
View attachment Shop side view 40' x 60' attic truss Model (2).pdf

These show the front of the building (60' side) and the end of the building (40' side). As you can see on the front of the building (60' side) my posts will be spaced a max of 12' apart to allow for doors and on the rear (not shown) the posts will be set at 10' spacing. Between the tops of the posts (around the perimeter) will be 2 - 2"x12" connecting the posts. These will be notched into the top of the posts on the front and back of the posts and will be lag bolted to the posts. The trusses I will have made will rest on these 2"x12" members. Assuming the truss company specs these trusses to be 2' OC, there will be 5 or 6 trusses supported by most spans.

Will the additional weight of an attic and the future crap in it be adequately supported by these 2"x12" members?

Is this why you do not see more attic type trusses in pole barns?

Would I be better off going with a more traditionally accepted type of construction (i.e. standard 2"x4" or 2"x6" framing methods)?

What do the experts think?

Tom

dodge man · Feb 10, 2009

I would want to know from the people who make the truss how much weight can be suppourted in the middle(your attic area). That area looks weak to me, but I'm just guessing.

RWolf · Feb 10, 2009

Not an expert by any means but to elliminate any loading problems you might look at doing a mesinine for storage. This way nothing is tied to the roof and the open area under the mesinine could be an office etc. Otherwise I think you will need some additional supports within the shop to support the attic. Check out some of the construction techniques on old horse barns.

dsb5610 · Feb 10, 2009

I am looking into building a shed as well and am interested in what others have to say about the attic. When I asked about this I was told I need to request the bottom chord be 2x6. Seems to me there needs to be a more scientific answer.

dsb

J_J · Feb 10, 2009

Tom,

Here are two that I found.

EddieWalker · Feb 10, 2009

The farther you free span the truss, the harder it will be to make it strong enough to support a load. In your first picture, it looks very weak.

The reason a second floor is so rarely done is because of how expensive the floor has to be. While it should be doable for an engineer to design a truss that will do this, it will be cheaper and easier to do it with posts or spanning the distance from wall to wall with I-Joists. 40 feet might be pushing it, so you'll have to see what's available and what its rated for.

Compare the cost of this to going bigger on the ground, and you'll see the reason it's how most people get the space they need.

Good luck,
Eddie

LarryD · Feb 11, 2009

While I'm no expert, I have been on projects where mezzanine floors were built and it is a pretty stout structure even for a 50PSF rating. I would love to see a truss structure rated for 50PSF that spans the distance you're planning just for reference.

I've got a friend that is just finishing up a mezzanine in a third of his typical pole barn and it really seems the most logical way to make extra storage. His building is 14' at the eve so the peak has to be at least 20'. He's got a lot of lumber in the floor and as Eddie said, it might be cheaper to just expand the footprint. If space is a limiting factor, a mezzanine might be the way to go.

framer · Feb 11, 2009

The cost per sq. ft. on attic trusses makes expensive lofts.40' truss maybe
16' clear span. Depending on pitch load design.Very heavy. Framer

Tscott9330 · Feb 11, 2009

Thanks guys. I think I am just going to go back with my first design with scissor trusses. I had planned a mezzanine on the right end wall. It would only be 9' deep, but a 9'x40' mezzanine would still hold a lot of junk. Other than that, does anyone have nay input on the design?

Tom

EddieWalker · Feb 11, 2009

Tscott9330 said:
...my posts will be spaced a max of 12' apart to allow for doors and on the rear (not shown) the posts will be set at 10' spacing. Between the tops of the posts (around the perimeter) will be 2 - 2"x12" connecting the posts. These will be notched into the top of the posts on the front and back of the posts and will be lag bolted to the posts. The trusses I will have made will rest on these 2"x12" members. Assuming the truss company specs these trusses to be 2' OC, there will be 5 or 6 trusses supported by most spans.

Will the additional weight of an attic and the future crap in it be adequately supported by these 2"x12" members?

Tom,

It sounds like you have the basics, but lack a few details and might be doing things a little excessive.

The size of the building is pretty good. I'm sure you've thought that through and it's what works for you. My shop is just 24x30, so that's what I work with.

You didn't say how tall your walls were going to be? Mine are 12 feet and I highly recommend that height. If you went lower, I wouldn't go below ten feet. My roll up door is 10x10 and that works great for getting just about anything into my shop.

The scissor trusses will give you more height in the middle, but they will cost you allot more money to build. When you price them out, be sure to also price out conventional trusses to compare the difference.

You said you want to put the trusses on 2ft centers. Why? This spacing is good for roof sheathing and then shingles, but for a metal room, it's a bit close and wasteful. From the picture, it looks like you have purlins on top of the trusses, which means a metal roof.

Spacing of the trusses is decided by the size of your purlins. Depending on code in your area and snow loads, the size of lumber and the spacing might be out of your hands. Here, we don't have snow and there's allot of variation on how it can be done. I personally like trusses on 4ft centers with 2x4x12 purlins on the flat on top of the trusses. Having them flat gives me a little more support and a bigger target to hit when screwing in the metal panels.

At six feet centers, you can turn the 2x4s on edge for your purlins and save some money on fewer trusses with the same number and price for purlins. The difference is flat or on edge. At 8ft centers, you go up to 2x6's for your purlins on edge. Then it just keeps going up from there.

I like my purlins to be every four feet. This gives me a very solid roof. My manufactures says I can go further apart, but this is what I like and how I do it. For the small increase in materials, it's worth it. I also like my purlins to be 12 feet long and I stagger them. First row starts at the end of the building, then the next one up goes in one truss and so on. 12 feet also gives me three trusses to attach to. 16 feet would be even better, but I've found that you have to use those 16 ft 2x4' pretty quickly or they tend to start to bow on you while sitting around on the job.

If you went with 8ft centers on your trusses,then you would have to use 16ft long purlins, but then of course, they would also be 2x6's with less tendency to bow on you then 2x4's.

You mentioned lag bolting your top plates to your posts. The notching is a good idea, but not really needed or necessary. Instead, use two or three half inch hot dipped galvanized carriage bolts. Three would be better, but I don't know your budget or code. Use screws to put them in place while getting them level and true. Leave the screws in there, but be sure to leave an open area for the bolts. This way it's easy to drill through all the wood at one time to install your bolts. Remember, nuts on the inside.

Eddie

radioman · Feb 11, 2009

which state are you from ? I didnt see anything in your profile. One thing you might want to consider is wooden I joists as they are much stronger then 2X12's. I see from the first pic your post in the ground is 3 ft . for a pole barn, you might want to go deeper for better bracing of the wind load. Around here where i live, I had to go 40 inches to get below the frost line as part of code. you might be able to get away with 36 inches further south. AS for your floor plan, I see your walls is 12 ft apart on the sides. Perhaps if you wanted to keep your design, you could add 60 ft metal I joists on each side of the 12 ft door. you would need to add posts to support the meteal i joists if your floor plan can afford it. Keep in mind , I am thinking like the northeast due to the snow loads issue for wieght supports.

Gary Fowler · Feb 11, 2009

I just about have this one finished (contractor built) and it has a 30 foot clear span with attic storage. Well I cant get the latest picture to attach so I will do it in another post

Gary Fowler · Feb 11, 2009

Another photo of amost completed 52 x 30 barn

Tscott9330 · Feb 11, 2009

EddieWalker:

You didn't say how tall your walls were going to be? Mine are 12 feet and I highly recommend that height. If you went lower, I wouldn't go below ten feet. My roll up door is 10x10 and that works great for getting just about anything into my shop.

I need the doors to be 12' tall, so I worked backward from there and end up with around 13' from the slab to the lowest part of the truss.

The scissor trusses will give you more height in the middle, but they will cost you allot more money to build. When you price them out, be sure to also price out conventional trusses to compare the difference.

You are right, I should get it priced both ways.

You said you want to put the trusses on 2ft centers. Why? This spacing is good for roof sheathing and then shingles, but for a metal room, it's a bit close and wasteful. From the picture, it looks like you have purlins on top of the trusses, which means a metal roof.

I just assumed the truss spacing would be 2' but I am going to rely on the truss company to tell me what I need. From reading your post, I think I would prefer spacing around 4'. I would like to be able to use 2x4's as purlins and nail to the longer side.

I like my purlins to be every four feet. This gives me a very solid roof. My manufactures says I can go further apart, but this is what I like and how I do it. For the small increase in materials, it's worth it. I also like my purlins to be 12 feet long and I stagger them. First row starts at the end of the building, then the next one up goes in one truss and so on. 12 feet also gives me three trusses to attach to. 16 feet would be even better, but I've found that you have to use those 16 ft 2x4' pretty quickly or they tend to start to bow on you while sitting around on the job.

I think in my drawing I had assumed purlins 2' OC but glad to hear 4' is acceptable.

Radioman:

which state are you from ? I didnt see anything in your profile. One thing you might want to consider is wooden I joists as they are much stronger then 2X12's. I see from the first pic your post in the ground is 3 ft . for a pole barn, you might want to go deeper for better bracing of the wind load. Around here where i live, I had to go 40 inches to get below the frost line as part of code. you might be able to get away with 36 inches further south. AS for your floor plan, I see your walls is 12 ft apart on the sides. Perhaps if you wanted to keep your design, you could add 60 ft metal I joists on each side of the 12 ft door. you would need to add posts to support the metal i joists if your floor plan can afford it. Keep in mind , I am thinking like the northeast due to the snow loads issue for wieght supports.

I am in north Florida, so snow load is not a concern.

Thanks for all the pointers guys

Tom

Tscott9330 · Feb 11, 2009

Ok, so here is the redesign of the shop. As you will see, I changed to a flat bottom truss, set the poles 4' deep, and spaced the trusses and purlins to 4' OC. I opted to keep the 12' wide doors if I can, I have a boat that I would like to be able to maneuver into the shop, and the extra width will help a lot.

View attachment Shop side view 40' x 60' attic truss Model (1).pdf

View attachment Shop side view 40' x 60' attic truss Model (2).pdf

Let me know what you all think. If I can get the county to OK these, then I will be in business. I can't wait to get started.

Tom

Also, do you see any other notes that need to be added?

EddieWalker · Feb 12, 2009

It's looking better. Two things jump out at me that you may want to consider. First, you have your wall purlins set inside your posts. They attach to the outside of your posts. Idealy, you want them to be long enough to attach to three posts so you can overlap your ends. At 12 foot centers, you'll need them to be 24ft long.

What are you using for siding? If it's metal, then 24ft long 2x6's will work. It also looks like you have them spaceds at 16 inches. With metal, 4 feet centers is all you need. For overkill, you can go three foot, but anything more then that is just excess material.

If you are using a wood material like T1-11, then two foot centers is needed. The same is true for Hardi over OSB.

The other thing that you may want to consider is the change in pitch from your truss to your lean to. Going from one picth to another meansh you create a transition. This may or may not create a problem for you. It's more work at sealing it. How much height do you need at the ends of the roof? If you need the height, go for the change in roof pitch, but if you still have plenty of height, and from what I can tell, you do, then keep the same pitch across the entire roof.

With the same pitch, water will shed faster and you will never have a leaf buildup at the transition of the two pitches. You will never have a leak there or bugs coming into yoru building from there.

Eddie

6sunset6 · Feb 12, 2009

It looks like your doors are right up against the ceiling line. Overhead doors need a little space to make the track curve. They do allow for a reduced height with a double track. Best to call the door guys and ask them how much room they need for the height of the door.
I have an 11' door in a 12'4" ceiling height. They said I could have gone a little higher but it works fine . 3" thick but in FL you don't need that.

Tscott9330 · Feb 12, 2009

First, you have your wall purlins set inside your posts. They attach to the outside of your posts. Ideally, you want them to be long enough to attach to three posts so you can overlap your ends. At 12 foot centers, you'll need them to be 24ft long.

I recall seeing a few buildings on here with he wall purlins between the post. I was under the impression that this worked well as it framed the interior walls at the same time as the exterior. Is this not the case?

What are you using for siding? If it's metal, then 24ft long 2x6's will work. It also looks like you have them spaceds at 16 inches. With metal, 4 feet centers is all you need. For overkill, you can go three foot, but anything more then that is just excess material.

I am not really sure yet what siding we will go with. The original plan was to go with OSB sheeting covered with Hardie board to match the house, but I am beginning to think that will be a lot more expensive than painted metal. How do the cost Compare? I guess to be safe I can set it at 2' OC.

It looks like your doors are right up against the ceiling line. Overhead doors need a little space to make the track curve. They do allow for a reduced height with a double track. Best to call the door guys and ask them how much room they need for the height of the door.

I know it is close, but I plan to use sliding barn doors on the outside.

EddieWalker · Feb 13, 2009

Tscott9330 said:
I recall seeing a few buildings on here with he wall purlins between the post. I was under the impression that this worked well as it framed the interior walls at the same time as the exterior. Is this not the case? .

Anything is possible, but some things are more expensive then others, and some are allot weaker then others. I'm not familiar with what posts threads you are refering to with the purlins between the posts. I have seen purlins on the outside of the posts to attach the siding, and in addition to those purlins, framing studs between the posts that rest on a cement foundation. I've never seen anything like what you drew and don't belive it will work. The weight of the lumber in the middle will sag unless you have it supported by something like a cement footing or addtional lumber in/on the soil.

Tscott9330 said:
I am not really sure yet what siding we will go with. The original plan was to go with OSB sheeting covered with Hardie board to match the house, but I am beginning to think that will be a lot more expensive than painted metal. How do the cost Compare? I guess to be safe I can set it at 2' OC. .

Matching the house will probably increase the overall value of your home to some degree, but it's up to you to decide if it's worth the greater expense. Metal is probably your best value for your dollar for siding.

Tscott9330 said:
I know it is close, but I plan to use sliding barn doors on the outside.

Sliders are cheap and easy to build yourself. They leak wind and rain, and will let the bugs in with out any resistance. They tend to wear fairly quickly and in a few years, will require fairly regular maintenance and repair. The better you build them, but longer they will last, but it will take a considerable amount of skill and experience to do this.

I have a roll up door and highly recomend them. If you can't afford one, wait until you can. There really is no comparison.

Eddie

MarkV · Feb 13, 2009

You may want to go talk with the county building inspector before you get to set on a plan. What some of the advisors here may not realize is that Florida has really up graded their building codes after the last few hurricanes. Contractor friends of mine in the Tallahassee area tell me they are having to build completely different than in the past to meet the new code wind load requirements.

Also as mentioned, if you have the room going narrower and longer might be cheaper per square foot of building. My experience has been that trusses over 32' jump in cost considerably.

MarkV