Roof structure

[Dorte]

I am NOT a builder. At all. My only experience is the little I helped my father back on our farm when I was younger, and honestly my father isn't much of a builder either...

Anyway, I have friends who can help and I am sure I can learn... I need some construction help though. Usually Google has the answers, but it is failing me on this one. Wrong keywords, I am sure.

Let me outline the idea for my coop first. It will be placed on an oddly shaped lawn next to our driveway. No way I can build the coop in odd angles, so my plan is to make a regular 4x6 coop with a flat roof that expands into the run for solid shade. I am in central CA, so it gets hot around here in summer. I cannot roof the whole run, but it is placed under trees that provides some shade, and the extended roof is meant to protect at least some of the run from rain and sun. The run will be an odd shape, but the roof will be square and I will somehow close of the gap with netting or something. The water will run off the roof to outside the run, and the plot is angled so it runs away from the run.

This is a very rough draft of what I envision:

I may be crazy to want to build it myself with my limited skills, now let me go completely insane: I have had a desire to play with green roofs for a long time, and this seems to be the perfect application! A green roof will (hopefully) be esthetically pleasing (my coop goes in the front yard) and it offers good protection from the summer heat with both evaporative cooling and large thermal mass. Plus a have a friend who is an expert on the plants for greenroofs. My main concern with the green roof is that it will be HEAVY, between 15 to 50 pounds per square foot (sorry for the wide range, that is what I could find. I am sure with my little roof I can design it to be closer to 15 than 50). We never have snow here, so no need to worry about extra weight from that.

I was planning on supporting the roof on 6 4x4's (or bigger?) posts, one in each corner of the coop and two under the extended section. The area of the roof will be about 65-80 sq. ft. I have studied coop designs with similar roof structures, but I have a hard time figuring out exactly how it is done and how strong the construction is. I'd much appreciate links that can help.

The angle of the roof on the drawing is 5 deg. It has to be above 3 deg for the water to run off properly, and I figured it was safer to go a little steeper. I am considering making it even steeper sacrificing height on the back side of the coop, but then I'd like to be able to open that side also to clean it out.

My specific questions:

1) Is 6 4x4's enough to support the roof?
2) What is the best (and easiest to build) design for the roof? How close does the rafters need to be?

Feel free to point out all the flaws you see in the plan....

 

[illegal avian]

Either white pants or a black shirt would look nice.

 

[NurseELB]

I'm not sure about clothing, but as far as the coop, I'd make sure you have very strong footings and then you should be fine.

 

[illegal avian]

Quote:
For a nice selection of strong footings you might want to consider LLBean.com for some ideas.

 

[Gypsi]

I kinda thought concrete footings - even the preformed kind: foundation strength dense concrete from home depot - would be more useful than new shoes. But ya never know, this is a california coop...

 

[Prospector]

For a more serious answer... (Although I do agree with some of the fashion suggestions, and wonder why no one has addressed what th ebest choice of socks is.)

Your loading may be more than you think. Take out your bathroom scale and a rubbermade or other tub. Put in as much dirt as you think you will have on th eroof (6 inches deep? 8? 12?) Saturate the dirt so its like a rainstorm just hit. Now check how much it weighs. measure the area of the tub in inches, and convert it to square feet. Now you have your loading persquare foot. But wait, thats only dead load.

On top of that you need to add live load. Are you ever going to be up there to tend to your garden? Will you be vigorously digging and pulling weeds, or will this just be grasses gone wild? How much would it suck to be up there with one of those 3-tine weeder thingies getting the weeds outta the tomatoes and have the whole structure come down? That would be even worse than having an aspen fall on your coop.

So however much the heaviest person plus the equipment they have up there weighs is the live load. Equipment could include a pail of water, liquid fertilizer, One of those sprayer things, whatever you will have up there.

Now we have a feel for the weights the roof needs to support, and the movement it needs to support, and you are thinking, hey, thats a lot of weight. Never fear, We have technology to overcome.

Your 4X4 posts may be able to support the load, but it will depend on how well anchored they are to the ground and how rigid of a structure the coop is. If you build the coop sloppy and use undersized fasteners, you are really asking for trouble here. If the coop is built solid, and the studs are spaced a little tight (maybe 12 or 14" centers rather than the traditional 16), with solid plywood sheathing to prevent shifting, you have a chance. I would make judicious use of bolts to attache the roof and floor as separate decks to the posts. Don't just nail them in place. You have too much loading for nails. A little twisting and they will start to work out of the wood. Nuts and bolts won't look as pretty but they will hold up better. Get galvanized carriage bolts to prevent rusting. Through bolt on 2 sides, so your beams running fore and aft and the beams runing lengthwise are all bolted to the posts.

With th ebeams secure at the top and floor level, your posts shouldn't move as much, and you may be able to support the load. Now tha tthe beams are in place you can think about rafters. a 3-5% grade may work, I don't know. If you put the roof up at 3%, you will need to find the joist size to support the load you measured above. There are floor joist sizing tables that should help you with this. As a guess I am going to say 2X10's spaced at 20" but that is just a guess. The run of your roof is pretty small, so you might find that smaller lumber will work. The tables will give you 2 considerations in sizing your joists - clear span and load. Clear span is the length of the joist that you can see lying on the floor. So you will have the clear span inside th ecoop, and then a second clear span out in the overhang. I would suggest setting up your joists so they sit on the wall of your coop and run out over the yard, sitting on a beam bolted to the posts at the far end. This means each joist wil lhave 2 clear spans. In the table look up whichever of these 2 spans is longest.

Here is an example of a span table: http://www.southernpine.com/pdf/table07.pdf This is for 60 pounds per square foot live load, and 20 pounds per square foot dead load (Major over kill, but its a small surface). It shows that ss (Standard Stud) grade 2X10's could support the load (60 live, 20 dead) if spaced at 24 inches, for a span of 10' 2" - which may be the size of your overhang (I don't know).

If I were you, I would subtract 1 foot from the lengths shown in the table, since you may be doing some vigorous work up there, and (as you said) your construction may not be at teh same level as the pros. By subtracting a foot, you allow for a little leeway. I also tend to over-build.

Hope this helps some,
Prospector.

 

[patandchickens]

What Prospector said. Load tables like that are very useful. So are books on building green-roofed sheds.

But there is one other thing to consider here.

YOu will be constructing a VERY VERY topheavy structure that is almost completely lacking in diagonal bracing. This will make it extremely fragile to sideways forces, such as wind or being bumped into. You do NOT want many many hundreds of pounds of roof to pull the whole thing over, parallelogram-wise, SPLAT the whole coop flat on the ground in splinters.

So, you will need to add MUCH ADDITIONAL DIAGONAL BRACING. Wire does not count, small portions of the walls covered in plywood do not count, you need SERIOUS DURABLE HEAVY-DUTY bracing. There are various ways to do it, depending on your aesthetic tastes (and tastes in construction methods), but DO NOT skip it!!!!!

Can I ask, though, what is the purpose of making it a green roof? It is not clear you'll get much benefit from it, especially if you go with the closer-to-15-lbs-per-sq-ft "brown roof" type designs... you'd have to have deepish soil and water it a bunch to get evaporative cooling, and the whole thing is so small that I have a prohibitively hard time envisioning that coop temperature will be more influenced by *roof* temp than by *air* temp. By all means do it if you want a significant engineering/construction challenge, but I honestly doubt you would get any PRACTICAL return from it. An alternative would be a metal roof, insulated underneath, from which you collect roof water for the chickens or garden...

JMHO, good luck, have fun,

Pat

 

[Dorte]

Thank you for the help! It is clear that my plan needs some modifications. The green roof is really just for fun (as are the chickens), I don't expect to get any real practical use from it that I couldn't get from simple insulation of a regular roof. At this point I have to decide if it is fun enough considering the complications it involves or start out simpler and safer. Right now I am definitely leaning towards the latter.

The fashion suggestions I will leave to Google, they made the man. To those of you who doesn't know the program it is GREAT if you need to sketch a project like this. The drawing I made below didn't take two minutes to make because it was just meant as a rough draft. I honestly think it would take me longer to illustrate it by hand. I left the guy in there because I figured it was useful for sizing reference.

Thank you Prospector for your detailed post, I realize now that I should have looked for information for FLOORS.

 

[Prospector]

No Problem Dorte, I hope you were able to make sense of it!!

I'm still figuring out chickens as well, so its nice when I can have some answers instead of questions!!