Coop roof questions...

Discussion in 'Coop & Run - Design, Construction, & Maintenance' started by corvidae, May 21, 2011.

  1. corvidae

    corvidae Chillin' With My Peeps

    488
    5
    111
    Feb 27, 2011
    Utah
    Okay, having never built a roof before (our other coop was a converted playhouse), I have a couple of what may actually be completely idiotic questions for the more experienced of you! We are building a 12' x 16' coop, walls made out of pallets. For the roof, what I was thinking waas a single pitch with 2 x 6's spanning the 12 foot side every four feet and braced with 2 x 4 pieces in between. The plan for the covering is metal roofing with Reflectix underneath to keep it from heating up too much (or losing too much heat during winter) and keep condensation down. We get a moderate amount of snow--usually melts off within a day or two, but can get those nasty storms that dump 2-4 feet at times. Does this plan sound like it would hold up to the snow load? Is polycarbonate better than metal for snow load (or anything else?)?

    Thanks-
    Donna
     
  2. fireguy56

    fireguy56 Chillin' With My Peeps

    533
    120
    161
    Oct 2, 2010
    Slidell, Louisiana
    Donna,

    First of all, there are no "stupid" questions. That's how we learn.
    Having a
    construction background i thought my might be able to make a few suggestions and ask a few qestions.
    1. Being in the south (Louisiana), I can't tell ya how to deal with snow, but I would definitely recommend metal over polycarbonate due to understanding the load put on any roof by snow. Not to mention light transparency which will help to heat up in summer.
    2. How much pitch along the shorter run are you planning? Are ya thinking one wall(ie front) 2- 3 feet or so higher than back wall, thus giving you a shed roof so melting snow can run off?
    3. Could go several ways on purlins. Blocking on flat between each joist or 1x4 material on flat perpendicular to rafters spaced about 36' apart. I would space the rafters no less than 24'' on center. Or if the budget allows , you could sheath the entire roof with an inexpensive material like OSB(plywood looking 4x8 sheets), covered with 15lb felt. Then you can fasten your metal in lines anywhere you want and won't take the chance of missing your purlins. Plus, much sturdier if ya wanna get up there and shovel the snow off.
    4. What will you be covering the pallets with? Or will it open coop with no covering? Just curious.
    5. Dirt floor or some sort of platform foundation?

    Hope this helps,
    Erik
     
  3. Bear Foot Farm

    Bear Foot Farm Overrun With Chickens

    5,545
    224
    288
    Mar 31, 2008
    Grifton NC
    nasty storms that dump 2-4 feet at times.

    Put your 2 X 6's on a 24" center and it should handle the load, although 2 X 8's would be better​
     
  4. patandchickens

    patandchickens Flock Mistress

    12,521
    86
    341
    Apr 20, 2007
    Ontario, Canada
    Your rafters need to be closer together, no more than 2' apart and possibly more like 16-18" (I'd have to look at tables to be sure, and am too lazy at the minute plus about to have to go make dinner, sorry).

    You need to make EXTREMELY CERTAIN that the top plate of the walls (at least the high and low ones) are strongly-enough engineered too, b/c remember THEY will be what's carrying the total weight of the roof plus all its snow. If you are wanting to use pallets I would extremely strongly recommend pole-style framing (just using the pallets to fill in the walls) using either 6x6s (pressure treated) if you want to use only corner posts, or a series of 4x4s set all along the wall (again, would have to look up tables for spacing but they'll probably have to be fairly close together.

    If you are going with 6x6 corner posts, you will need some really pretty serious beams (the plate at the top of the wall, on which the rafters rest), I live in an area with comparable-or-smaller snowloads and when designing my horse shed, which has 10x12' bays, had to use doubled 2x10s or 2x12s (I forget which) and your span will be longer than mine is so you may have to go to *trebled*. (This gets expensive, and also good exercise to put up there). If you use a bunch of 4x4 posts all along both loadbearing walls, you can get away with less-serious beams, the exact details depending on the spacing of your 4x4s. Consult engineering tables.

    Seriously, that is a lot of weight and you need to design for it to be well-supported or you're going to go out there one morning and find your roof caved in on your hens. Do it right the first time [​IMG] It is certainly very doable, I am not at all trying to be discouraging, it's just important to actually find these things out BEFORE putting anything together [​IMG]

    Good luck, have fun,

    Pat
     
  5. corvidae

    corvidae Chillin' With My Peeps

    488
    5
    111
    Feb 27, 2011
    Utah
    Oh, yeesh, we are going to need a few more 2 x 6's it sounds like (actually, sounds like 2 x 8's are the better option, yes?). The pallets are going to be covered with a whole buttload of hardwood (oak and such) simply because the guy that lives across the street from us had tons and tons of it sitting around that we were given for free. The problem with it is that none of it was more that 2-3 inches wide, so we are making panels out of all of it to go over the pallet walls. The corners are only 2 x 4's, so it sounds like we may have to put some poles for support in the middle of the coop? The floor will be dirt--we are planning to do DLM and want the at least marginal warmth from it in winter. We already actually have the pallet walls up-- they run 6'6" high and I was planning to frame up a higher part on one side to accomodate the rise. How high up should I be going? Would we be better off doing a double pitched roof (like a normal house)? Which way is it actually stronger, or is it simply a matter of support down the middle? I don't mind putting a bit more money into it, since it seems that would be better than finding a bunch of dead chickens and a big pile of collapsed wood. [​IMG] My welder friend who is helping to build this is using steel straps he made to reinforce the corners--he didn't seem to feel that screwing the wood together was sufficient stability. That, and I think he just like throwing steel on everything. [​IMG]
     
  6. patandchickens

    patandchickens Flock Mistress

    12,521
    86
    341
    Apr 20, 2007
    Ontario, Canada
    Quote:No, 2x6s are probably the correct size, you just have to get them at the right spacing.

    But the thing is, that's not your BIGGEST strength issue -- the biggest issue is the engineering of the wall top plates (or beams, if it's pole-type construction) that HOLD THOSE RAFTERS UP.

    The corners are only 2 x 4's, so it sounds like we may have to put some poles for support in the middle of the coop?

    Having poles down the middle would help reduce the load on the two bearing walls, but not REMOTELY to the extent of just being able to use 2x4s and pallets and expect it to hold up. Honest, you are going to have to invest in 4x4s or bigger (or something comparable -- in some cases, round cedar farm-fence posts can be nearly as good and cheaper, only it is hard to get the 5-6" diameter ones you need in long enough lengths to make a walk-in height building if they are also being set adequately deeply.) Otherwise, there is a very, very high chance it will all go flat within the first winter, given the size of the building and your snow conditions.

    (edited to add: well, there is one alternative way to go. Find a way to add vertical 2x4s to your wall every 16" or so -- they must be absolutely vertical and absolutely continuous from top to bottom, not 'stacked pallets strapped together and we'll say that they're *like* a 2x4' -- and top it with a 2x4 or 2x6 on flat, so it is effectively sort of a stud wall. That might be adequate too. I don't know whether your wall construction lends itself to doing this or not)

    I was planning to frame up a higher part on one side to accomodate the rise. How high up should I be going?

    If you are using metal roofing, a 2:12 pitch is marginally-ok (more is better). If you are going to be doing a shingled roof, you'd want more like 3:12

    Would we be better off doing a double pitched roof (like a normal house)? Which way is it actually stronger, or is it simply a matter of support down the middle?

    It's mainly aesthetics, honestly. And which way you want the runoff going [​IMG] There is not a huge lot of difference in the engineering. You can do either way WITH posts down the center, or you can do either way without (so it's clearspan).

    I don't mind putting a bit more money into it

    First look up what support you need (and you can look up different options, e.g. with vs without center posts, and with different wall-post spacings [which affects how heavy a beam you need to build] so you can price it out different ways and make a sensible decision)

    Then invest in the necessary amount of p/t 4x4s or 6x6s (depending on how you decide to build) plus the necessary 2x8-10-12 stuff required to build adequately strong beams.

    Really really [​IMG]

    You can maybe cheat a little on the table values you find, since this is not going to be human occupancy (and, having a steeper-pitched metal roof also helps you get away with less support, since snow slides off better)... but there is a real limit to "how low you can go" and still expect it to hold up.

    JMHO, good luck, have fun,

    Pat​
     
    Last edited: May 21, 2011

BackYard Chickens is proudly sponsored by