I am posting this as a public service announcement on accounta at least one BYC member has *already* posted about their coop/run being flattened by snow, and it is not even November yet. (Thus, you have time to do it while it's still decent working weather, but ought to do it before you too get a freak wet snowstorm that tests your setup's engineering)
(edited to add, since horsejody's post below made me realize what i forgot to mention, the following is really aimed at those with new(ish) coops
)
The weight of snow varies depending how dry/powdery vs wet/slushy it is, and will change as it compacts with drifting or settling, but a reasonable rule of thumb is that snow accumulating on a roof will weigh in the vicinity of 5-20 lb per cubic foot, up to 50 lb per cubic foot if there is rain involved too. If you care about knowing actual numbers to be engineering for, your municipal zoning office should be able to quote you a snow load number (note that this will represent what can be expected from a particularly bad storm, not from a typical winter)
Realistically most people are not going to go into structural tables to figure out what snowload their coop is good for, however (tho frankly it is kind of entertaining to work out, if you like that sort of thing
). I would at least suggest that you take one of the folllowing two approaches: either a) ensure that your structure is built with the same post size/spacing, beam size, rafter size/spacing, and (if applicable) purlin size/spacing as a number of other buildings in your area that have been standing for at least a decade; or b) go beef it up as much as you realistically are gonna do.
One thing that will really strengthen a raftered roof is to use collar ties (google if you are not sure what I'm talking about), a piece of 2x4 or 2x6 that runs horizontally between the two rafters of a pair, a few feet below the peak fo the roof. This prevents them from "doing the splits" and letting the roof collapse.
Another thing that will strengthen a building is to add diagonal bracing, since another common mechanism of collapse is for a box-shaped building to become parallelogram-shaped and then flat. If you have heavy plywood siding well-screwed on, you are prolly ok; but with anything else, especially just wire mesh or tongue-and-groove boards, it is really worth running a coupla 2x4s diagonally on (or in) each wall, screwed to all the studs. (there are less conspicuous ways to do it too)
You think your run can't collapse because the top is mesh, and snow will jsut fall through it? Think again. (Or go browse last year's coop design section, in which you will see pics of a lot of flattened mesh-top runs). Unless it is a dead-dry powdery snow, it easily starts to accumulate on the wires, and frequently becomes a solid snowpack up there, with all the weight issues that go along with it. Freezing rain can be a bad problem in some areas too.
Netting will come down under stress from snow or ice, hopefully just pulling/ripping free of its supports; chickenwire will stretch; but wire can also easily *pull down* its supporting structure, sometimes causing a lot of hard-to-fix damage.
One easy fix is to add support posts in the middle of your run, under the 'rafters' that support the mesh top. Rotate the 'rafters' if necessary so they are narrow edge up, btw, not wide edge up the way many people install them - this is much stronger. Don't just prop the post there, actually screw it (directly or using galvanized fixings) into the structure atop it, and peg it very securely into the ground, so it will not simply fall over under snow load. (Yes, they do).
Diagonal braces help too, as described above.
And think verrrrry carefully before putting roofing sheets or a tarp onto a minimally-supported run top. You may *think* all the snow should slide off or that you will go out and knock all the snow off before it accumulates too much, but realistically this scenario seems to result in a lot of damaged or flattened runs.
Finally, those in southern or coastal climates, where snow is rare (but does happen sometimes), should probably take heed at *least* as much as more northerly or -inland people. Because when it DOES snow in 'borderline winter' climates like that, the snow is almost always very wet, often mixed with rain or freezing rain, and it takes a lot less of that to mash down your coop or run than it takes -20F powder snow
Really, think about those numbers -- are you SURE your run top and roof can handle them, both in terms of point loading and in terms of the support for the whole shootin' match? If not, NOW is the time to beef things up. It's a lot easier than *picking* things up later.
We now return you to your regularly scheduled "warm wet late October weather" (at least that's what we've got here, just rain),
Pat
(edited to add, since horsejody's post below made me realize what i forgot to mention, the following is really aimed at those with new(ish) coops
The weight of snow varies depending how dry/powdery vs wet/slushy it is, and will change as it compacts with drifting or settling, but a reasonable rule of thumb is that snow accumulating on a roof will weigh in the vicinity of 5-20 lb per cubic foot, up to 50 lb per cubic foot if there is rain involved too. If you care about knowing actual numbers to be engineering for, your municipal zoning office should be able to quote you a snow load number (note that this will represent what can be expected from a particularly bad storm, not from a typical winter)
Realistically most people are not going to go into structural tables to figure out what snowload their coop is good for, however (tho frankly it is kind of entertaining to work out, if you like that sort of thing
One thing that will really strengthen a raftered roof is to use collar ties (google if you are not sure what I'm talking about), a piece of 2x4 or 2x6 that runs horizontally between the two rafters of a pair, a few feet below the peak fo the roof. This prevents them from "doing the splits" and letting the roof collapse.
Another thing that will strengthen a building is to add diagonal bracing, since another common mechanism of collapse is for a box-shaped building to become parallelogram-shaped and then flat. If you have heavy plywood siding well-screwed on, you are prolly ok; but with anything else, especially just wire mesh or tongue-and-groove boards, it is really worth running a coupla 2x4s diagonally on (or in) each wall, screwed to all the studs. (there are less conspicuous ways to do it too)
You think your run can't collapse because the top is mesh, and snow will jsut fall through it? Think again. (Or go browse last year's coop design section, in which you will see pics of a lot of flattened mesh-top runs). Unless it is a dead-dry powdery snow, it easily starts to accumulate on the wires, and frequently becomes a solid snowpack up there, with all the weight issues that go along with it. Freezing rain can be a bad problem in some areas too.
Netting will come down under stress from snow or ice, hopefully just pulling/ripping free of its supports; chickenwire will stretch; but wire can also easily *pull down* its supporting structure, sometimes causing a lot of hard-to-fix damage.
One easy fix is to add support posts in the middle of your run, under the 'rafters' that support the mesh top. Rotate the 'rafters' if necessary so they are narrow edge up, btw, not wide edge up the way many people install them - this is much stronger. Don't just prop the post there, actually screw it (directly or using galvanized fixings) into the structure atop it, and peg it very securely into the ground, so it will not simply fall over under snow load. (Yes, they do).
Diagonal braces help too, as described above.
And think verrrrry carefully before putting roofing sheets or a tarp onto a minimally-supported run top. You may *think* all the snow should slide off or that you will go out and knock all the snow off before it accumulates too much, but realistically this scenario seems to result in a lot of damaged or flattened runs.
Finally, those in southern or coastal climates, where snow is rare (but does happen sometimes), should probably take heed at *least* as much as more northerly or -inland people. Because when it DOES snow in 'borderline winter' climates like that, the snow is almost always very wet, often mixed with rain or freezing rain, and it takes a lot less of that to mash down your coop or run than it takes -20F powder snow
Really, think about those numbers -- are you SURE your run top and roof can handle them, both in terms of point loading and in terms of the support for the whole shootin' match? If not, NOW is the time to beef things up. It's a lot easier than *picking* things up later.
We now return you to your regularly scheduled "warm wet late October weather" (at least that's what we've got here, just rain),
Pat
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