Structural question about a 3 sided lean to (for livestock)

So I need to build a 3 sided lean to in order to provide some basic protection for Alpaca.

I need the building to be 8x12, with the slope going up the short side. No floor is needed.

My plan is to use pier blocks for the foundation. 4x4 posts braced in place with either horizontal 2x6 or 2x4s. Then mount siding on the horizontal boards. I am thinking the posts will be 5.5 on front, 7 in back. So the height will be that plus pier blocks.

My question is relatively simple... for an 8x12 structure, how many pier blocks will I need? One every 4 feet? Just the 4 corners?

do i need 2x4s or 2x6s? Do I need top middle bottom, or just top and bottom? I'm going to need to put rafters on for the fiberglass corrugated roofing, does that load change anything?

Also... if I have posts at 4 feet, i could mount siding to posts instead of horizontals and have those on the inside. Or i could have the horizontal boards on the outside and mount to them... i assume this second version is superior? But i dont know for sure.

thanks for any advice!

 

I can't really rubber stamp your idea, if you get any high winds, that thing has the potential to be like a large kite. Instead of blocks, I would recommend sonotubes and post bases, so that the structure is at least solidly anchored down. So I can't really comment much on your questions as I don't agree with the premise of building on blocks. Putting posts in the ground and backfilling with rock would even be better than building on blocks, IMO.

Open structures catch a lot of wind, so the issue is uplift.

You don't necessarily need siding, but you should likely have some structure to keep the posts plumb and the walls square. That's usually accomplished with a single diagonal brace on each section of wall on a freestanding structure, but if this is a lean to (attached to another building) then that building provides the structure needed to plumb and square the walls.

Can't really comment much, since the plan is pretty vague. If your front is open, then you either need a beam in front for the rafters to sit on and you would need purlins laid perpendicular on top of those rafters for your roofing to fasten to. Alternatively, your side walls could be built in such a way to provide the correct pitch for the rafters... in other words if your side walls are the load bearing walls, your rafters then could run parallel to the front wall, and there would be no need for purlins for the roofing. (But purlins are nicer to walk on and give you a larger area for the roofing to fasten to.)

 

Hmmm, no, I don't want rubber stamps, I'd prefer critical issues be pointed out.

I had thought about the issue of wind but figured it would have enough weight and some venting to dissipate any wind (Pacific North West). The venting would (or would have, potentially) been the triangles between the siding on the low side and the top of the rafters (so, 1.5 foot by 8 foot triangles, left and right). I could also cut vents in the back wall if necessary... and it will also have some venting at the bottom since it sits on piers in the current design. But I totally understand how air could potentially get up and under the roof, causing issues.... i wonder if that is an issue regardless of the structure for the corrugated roofing...

I could put posts into the ground... though that would require a lot of digging I guess. How deep would you recommend if I went that route? For better or worse I already bought some of the lumber.

the original plan does have a 2x6x12 across the top of the front to hold rafters. All posts are held together by the horizontal 2x6s, plus siding on top of that.

The structure needs to basically just provide wind and rain protection for Alpaca, who generally do not care about cold. We also have a barn to put them in at night if necessary, this is a recommended building for them to nap in, basically.

I would appreciate any help getting this to a point where I am not putting anyone or thing in harms way. I have a supply of 4x4 posts (some 8 and 10 footers), piers blocks, siding, 2x6s, 2x4s, and corrugated roofing... i was envisioning this to be a relatively simple build (we just built a tank like shed as a coop... since this was just 3 sided and didn't need predator protection i was trying to go easy on time and money.

it is freestanding, not part of another structure.

i can provide a better diagram of my original plan if it helps to visualize it, but the main goal is an 8x12 3 sided structure (though as in the picture above we had part of the 4th wall covered.

 

I discovered the building is called a 'run in' when dealing with horses, I assume the same for alpaca, The end result I am going for shape wise is 8x12, something like:



But constructed differently. Posts on pier blocks connected by multiple 2x6s and then clad in siding. Open top triangles like the one above for ventilation.. so visually a bit more like below.




Again, constructed differently but similar goal.

 

wind could be an issue but being open partially should help would still consider the way its facing for your area and how much wind it may see under the roof in a storm. setting post in the ground or even just anchoring to the piers some way would very likely prevent the structure from blowing over do to the added weight of the concrete pier otherwise it looks like a simple build to me.

 

Thanks, @alan73

I agree it's a simple build... unlike the coop/shed I just built I didn't draw this out at all and just bought the wood based on the image in my head.

In fact, my biggest concern was that I was over building and bought too many posts. I was thinking a post every 4 feet at first (breadth of siding) but nowI am wondering if I could get away with less posts.

live Iin Oregon so we generally don't get too much wind, and there will be significant venting, though I do want to be careful not to make something dangerous.

 

I'd be inclined to use the extra posts so you have stouter walls.I don't know much about alpacas but you don't want them kicking or otherwise weakening the walls.

 

Alpaca are gentle, and shouldn't damage it.

i did some more research and decided to do posts every 4 feet. That means 4 on the back wall, then 2, and then I will do 4 again on the front... except on the front, the extra 2 will be 2 feet away from the outside wall leaving an 8 foot open stretch (2 foot wall, 8 foot open, 2 foot wall) to add some integrity.

My father suggested simply drilling some holes with a hole saw in the back wall (swiss cheese) to relieve any potential wind sail issues. We are also thinking about adding a concrete foundation to the front posts, though I am unsure about that. I fear if I don't solve for wind, even if I could keep the structure on the ground I'd just cause roof panels to sheer off which is still dangerous, so I think perhaps I need to provide a way for the wind to escape regardless of foundation. The alpaca do not care about cold as much as heat and rain, so swiss cheese on the back wall might provide more summer ventilation and not matter much in the winter.

i have looked at a lot of online pictures and many run ins don't seem to take any of this stuff into consideration so hopefully i'm not over designing.

 

different types of corrugated roofing but would probably suggest metal roofing, you mentioned fiberglass in your original post if its the thinner stuff that allows light to transmit through probably wont hold up very well just not strong enough it cracks and breaks around the fasteners. and typically when you see it used in pole barns or garages its only in small sections to make a sky light effect.