Engineering question on rafters

[River Lizard]

Thanks all !!

Another thing I don't think I mentioned before is the metal roof panel grooves will be running the direction of the length of the building to match the carport (which I don't like but don't have a choice now that they installed the panels on my carport that way) this will "catch" snow more and not allow for it to slide off when melting.

After the comments, I'm leaning towards just upgrading the 10' x 10' section to 2' x 6' rafters and raise that area another 14" to give me plenty of headroom (I'm 6' 4" so I need all the headroom I can get!!)

I'm sure as I go along I'll be asking for all your opinions on a number of issues since I'm working from a blue-print drawing in my head!

I'll definitely put cross bracings between the 2' x 4's over the nursier/supply room. I'll also increase the sub-roof from 1/4" to 1/2" plywood as recommended.

Thanks everyone, it helps to get some suggestions from ya'll.
Appreciate it.

 

[cmjust0]

Check out this link .. It's the American Wood Council's span calculator.

I think I'd go with 2"x6" rafters, too... I spanned just over 10' with 2"x6" floor joists in my coop, and it's fairly bouncy. I can't imagine spanning that with 2x4s.. Granted, you won't be walking on it, but snow gets heavy! (I knew my floor would be a little bouncy, but I don't plan on spending much time walking around inside the coop...plus, chickens are light and don't require much furniture.

)

Here's a little tidbit to keep in the back of your brain for future reference: The bending strength of a joist or rafter is equal to the square of its depth. While the number that comes out the other side of that equation doesn't necessarily tell you about maximum live loads or anything like that, it will give you an idea of how much stronger one board is than another.

For instance...take the "4" in 2x4, and square it. 4x4=16. Now, look at a 2x6...6x6=36. So, right there you can see that a single 2x6 is more than twice as strong as a 2x4. Practically, what that means is that you can't scab two 2x4s together and make something quite as strong as it would be with a 2x6..

For a 2x8, 8x8=64...that means it's four times the strength of a 2x4, but not quite twice the strength of a 2x6...so, four 2x4s scabbed up is roughly equivalent to a 2x8, but two 2x6s would be stronger still..

That equation has helped me a bunch.

 

[River Lizard]

Yeah, I was going cheap and I shouldn't have ( I know better than to do that) but I started thinking about the $$ times how many rafters I was going to need and took the cheap route! Then I've been stressing over it ever since...it always came up in my mind when I was building the walls this last weekend...a little part of me was telling me "don't use 2 x 4's for the rafters!! It's too much of a span to be running that thin of a board." So after three days of torment, I thought I'd better seek out opinions here before I reached the point of no-return!


Now since I have let out my tormented thoughts.....I might as well let this one out too (it's been bugging me also).
Building wrap....what's your opinion on using it before I put the siding on? It's $99.00 a 150' which is way more than I need. I'm planning on using Hardy Board (concrete and fiber) for the siding on the whole coop.

 

[Intheswamp]

Quote:
Ah, the innermost conflicts of man...

You could go the 15# felt route...not sure about the cost savings, would take a bit longer to install, and would not be as vapor sealed as the wrap would be but it was used for years. Or, you could look around for a builder and see if they have any remnants or if they'd cut off the amount you need.

Just some thoughts,
Ed

 

[Big Chicken Little]

I used Hardy Plank siding that i had left over from building my house and did not use a vapor barrier as I felt that it is a coop and not a living space for humans. It is hard not to do everything 100% all the time which is how i do things Have fun !!

 

[River Lizard]

Quote:
My thought on using it was to possibly cut out the need for adding heat for the winter time. I've got the tall side facing South and will be adding several sets of windows to that side and 1 to the East side for thermo heat, so I was hoping to not have to have any type of heater other than maybe a community heat lamp for them.

Yesterday my wife drops a small bomb-shell on me......
"Honey, it would be great if I had a water source in the supply room"

Let's see, I just got done installing the sub-floor and had 1 wall up when she brings up plumbing!!!

So not only do I have to figure out running the water line (which isn't that hard) BUT trying to figure out how to add a drain line and run it to the other side of the chicken coop to whether the ground slopes down. I'm really trying hard not to think about that whole plumbing project right now!!

 

[annek]

I didn't put wrap on my coop but opted instead for standard tar paper. The vapor wrap isn't going to gain much in my opinion when we cut holes in the walls and leave it open for ventilation. The tar paper is more to protect my wood from moisture than anything else. I did my exterior in hardiboard also, I ripped off the cardboard crap that was up there, it was pretty much sawdust anywhere that water got on it anyway.

I also agree on going with the 2x6 and not 2x4, 11' is way too far of a span for that size unless supported 1/2 way across with another joist. Bad thing about when they sag, the middle would drop and become a great source of leaks.

 

[annek]

Quote:
My thought on using it was to possibly cut out the need for adding heat for the winter time. I've got the tall side facing South and will be adding several sets of windows to that side and 1 to the East side for thermo heat, so I was hoping to not have to have any type of heater other than maybe a community heat lamp for them.

Yesterday my wife drops a small bomb-shell on me......
"Honey, it would be great if I had a water source in the supply room"

Let's see, I just got done installing the sub-floor and had 1 wall up when she brings up plumbing!!!

So not only do I have to figure out running the water line (which isn't that hard) BUT trying to figure out how to add a drain line and run it to the other side of the chicken coop to whether the ground slopes down. I'm really trying hard not to think about that whole plumbing project right now!!

If you want to help with heat, go with insulation. The vapor barrier isn't going to help much without insulation being installed. I used the rigid pink foam so I didn't have to worry about my walls getting wet if I decide to hose the coop out.

On the drain, you could send it to a gravel pit anywhere. Just dig a hole, fill it with gravel for drainage and put in your pipe. It is not like you would be running water in it constantly and it would be gray water, not black.

We are in SC but ran our pipes on the outside of the building up from the ground. I figured I could insulate it better outside and my chicks would pick it apart if inside. I ran the water to the uninsulated mini run that is part of my coop, so I will have to shut it off a few times a year when we get a hard freeze.

 

[patandchickens]

Vapor barrier is not in any way whatsoever going to decrease the 'need' for heat or help the coop hold in warmth. If anything, in some situations it may make the indoor air incrementally damper, thus causing frostbite at (slightly) less-low temperatures. (And IMO it is highly questionable whether most coops should have an intentional vapor barrier...)

Are you suuuuuure you really want to put your roofing on the wrong way just to match the carport's being on wrong? That just doubles the area on which you have problems with snow accumulation and roof leaks. I'd think it'd be best to have at least HALF the roofing (i.e. the new coop) done in a correct and functional manner...

And I'd use 2x6s, fwiw. It won't cost that much more, and is FAR likelier to result in a durably strong/straight/plumb/nonsaggy structure.

Good luck, have fun,

Pat

 

[River Lizard]

Quote:
Yeah I know, if I could really afford it, I'd pull the sheet metal back off the carport and hang it the correct way also. Since I'm running 16" on center for the rafters, I shouldn't have a problem hanging the sheet metal the correct way unlike the carport rafters, which are some odd-ball width between 4' and 5' ft. That's why they installed them the way they did.

I'm going to switch to 2 x 6's and just use tar paper/felt as the backing on the sides. I was hoping to just stop any drafts from coming into the coop using the vapor wrap. I'm going to insulate with styrofoam on at least the North and West sides of the coop for sure and play it by ear on the other two sides.

As far as the drain system, I was planning on digging a pit and installing a 55 gallon plastic drum with holes drilled into it at the bottom that drains into a bed of rocks and then run a PVC pipe from the top to about 2 inches from the surface so if I ever need it pumped out, I can have them just draw from the PVC pipe. I don't think in my life time I'll ever have to have it pumped out since the slop-sink isn't going to be used that much .

I'll see if I can't sit down tonight and get some drawings done and post them up on my BYC page on some of the design ideas for this project and see what you think about them.
Thanks everyone for your input!