A wind-tested roof for the Chicken McMansion (Part 2)

Discussion in 'Coop & Run - Design, Construction, & Maintenance' started by Chieftain, Jan 9, 2010.

  1. Chieftain

    Chieftain Chillin' With My Peeps

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    https://www.backyardchickens.com/forum/viewtopic.php?id=280847

    In
    the above thread, I built a solid foundation that is critter proof and suitable for the high winds here in the Columbia River Gorge. You have probably seen the recent video on the news that was taken at Crown Point Oregon the other day, when the sustained winds at that point were 100 MPH. We didn't get that kind of wind here, but we did have sustained winds in the 40's with gusts up as high as 60 mph. That's enough wind to ruin any kind of structure that is not anchored properly, so please review that thread to see how we got to the point we are at today.

    I am installing a double beam supported roof that slants one foot to the rear. The front posts were cut off level at seven feet above the top of the foundation timbers, and the rear timbers were cut off level six feet above the top of the rear foundation timbers. The two beams are made from 12' lengths of 4x6 green Douglas Fir. It is inexpensive, and it will not rot, ever. (The East span that carries I-5 over the Columbia River at Portland, OR was built 103 years ago on top of multiple douglas fir pilings that were driven 50 feet into the bottom of the river, and they are still there today.)

    I prepared the timbers by measuring the layout between the base of the 4x4 posts, and carefully drawing it out on the timber. Then I used a countersink bit to bore a 3/4" deep hole, then switched to a 3/8" auger and drilled holes nice and straight all the way through the 6" dimension of the timbers, in three spots on each timber.

    [​IMG]

    Once I got the timbers into position on the posts, I dropped an 8" long by 3/8" diameter carriage bolt with a washer into each hole, and used my air impact gun to drive each bolt tightly down into the center of each 4x4 timber. You can feel the assembly solidify as the bolt draws down.

    [​IMG]

    [​IMG]

    As you can probably tell, this assembly is extremely rigid. It is not overkill to use a timber that size. It fits perfectly on top of the post, and the size of it means it will never sag between the posts as a 2x4 surely would. By using a solid beam like this, it will also break up any wind that does get under the roof as you will see...

    Now it is a matter of fitting the roof joists into place. i am using 8' green Douglas Fir 2x4 for roof framing. I designed and built my roof for a specific type of roofing, a corrugated foamed polycarbonate which you will see soon. I chose to frame the entire roof on 12" centers to simplify things in a number of ways down the road. The material I am using for roofing is opaque, dark green in color, very light weight, and the manufacturer offers a neat pamphlet at the Home Center that explains exactly how to install it, what other materials you need, and especially the special fasteners that you need to secure the material properly. You must choose your own roofing material, and design and build to that. My design needs to be waterproof and wind proof, and be able to support a moderate occasional snow load.

    The first step is to locate, mark and cut a pair of "birdsmouths" on the 2x4 roof joists. Friction is what holds wooden buildings together, and the fasteners you use merely squeeze the parts together in order to maximize friction. If you make sure that two pieces of wood touch with the maximum amount of surface area, your joints will be very strong. (I won't describe how to make a birdsmouth, it is a carpentry skill that is explained elsewhere). I laid out and cut all of my joists to length and cut both birdsmouths in my shop on a rainy day.

    I also cut a series of 10.5" 2x4 spacers to fill the gap between the joists, to provide a further attachment point to the 4x6 beams, and to provide a nailer to support the roofing down the center of the roof.

    [​IMG]

    A word on assembly. I used my air nailer with 2" galvanized wire nails to do all of my assembly and to immobilize the parts, and then came back and secured everything to the main beams with 3.5" construction screws. Screws will never pull out, and you avoid bursitis in your elbows if you don't go swinging a framing hammer several million times. I use "Gold Screws" because they are stainless steel, are very strong and are very easy to drive. I buy them by the five pound box, and this project will use several different sizes.

    [​IMG]

    Add a joist, screw it down, nail in the spacers, repeat.

    Once all the joists were in, I added another 2x4 to the front and the back. I used a large C-clamp to help align everything, and the front cap is double-screwed into each roof joist. The front support for the roof panels will be nailed to this 2x4 so it must be rigid and well supported.

    [​IMG]

    [​IMG]

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    Once you have everything attached firmly with enough screws, you will be amazed at how rigid the entire structure is, and that's good because now it's time to roof it. Again, what you do now depends entirely upon what kind of roofing you have chosen and how the manufacturer recommends you install it.

    My roofing started with a set of the corrugated supports air nailed in position, then each 26" sheet was progressively added and screwed into place. My screws had an EPDM rubber gasket on each one, and a quarter-inch drive bolt head; so I got a 1/4 drive socket for the power driver and used it to install the screws. They are so sharp that they drill neatly through the foamed plastic and into the roof joists. My roof turned out incredibly strong, and the winds of the past few days have proven how durable it is.

    You can also see how the beam and the spacers between the joists act as a solid wind break across the entire length of the beam, and it protects the whole structure from gusts.

    [​IMG]

    Looks really good, and best of all, no leaks! I'm on to building the coop now that I can work under cover with no danger of getting wet. And the whole structure is now so incredibly strong, It's very satisfying to give it a pound once in a while just to feel how solid it is...

    I will shortly be putting up another post that begins to detail where I am on the McMansion itself.

    Cheers!!

    [​IMG]
     
  2. Janos&Jen

    Janos&Jen Out Of The Brooder

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    That looks great...Can't wait to see how it all turns out!!
     
  3. SOchick

    SOchick Chillin' With My Peeps

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    looking good!
     
  4. crazy_4_chickens

    crazy_4_chickens Out Of The Brooder

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    I LOVE it!!!!! [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     
  5. Chieftain

    Chieftain Chillin' With My Peeps

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    Thanks! Let me tell you, it has been thoroughly wind tested here over the past two weeks, with some serious steady winds in the forties with gusts into the 60s lasting for several days. Nothing leaks and the roof doesn't even rattle...good enough for me!

    I've been working under cover now for several weeks and it's made all of the difference.

    [​IMG]
     
  6. patandchickens

    patandchickens Flock Mistress

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    Uh, I hope you are aware that untreated doug fir certainly *does* rot; even the heartwood is only of sort of intermediate rot-resistance compared to other wood types. The reason you it lasts as bridge pilings "forever" is that they are UNDERWATER, where NO wood will rot much due to low oxygen levels, that is why people make lotsa money these days fishing up long-submerged logs and dead trees from old-growth forests and can sell them as high-grade lumber. It's still quite a reasonable choice for aboveground parts of the coop, I am just pointing this out so that others reading it do not think that fir is rotproof or is as rot-resistant as (say) heartwood cedar.

    I am confused about how the beams are attached to the posts, though. You can't be using actual carriage bolts if they're going vertically down into the center of the posts, because they would not be coming out the other side to attach the nut to... do you mean you're using lag bolts (aka lag screws), which do NOT emerge on the other side and *could* be installed with a washer and driven by an impact driver??

    If you do mean lag bolts, then can I suggest a hurricane tie of some sort to attach the beam to the posts? Right now, the only thing keeping wind from lifting that (rather wind-catching, because it's a steeply pitched shed roof) top off the posts is the weight of the lumber and those few screws (lag bolts are really screws) sent into the *end grain* of the 4x4 posts. Screwing into end grain is really not a durable or strong proposition -- it always SEEMS fine at the start, but as the wood wets and swells and shrinks, and especially as it begins to soften and rot a little bit over time which I assure you it will even if you caulk that joint, it takes hardly any loosening of the wood fibers to permit the screw (lag bolt, whatever) to pull out really rather easily indeed. It would be really cheap and easy to put a metal plate or metal strapping up on each post-beam union, to tie them strongly together in a way that the wind will not be able to disassemble.

    Not criticizing, it'd just be a shame to see such careful work and nice materials wasted in a few years because of just one weak point [​IMG]

    Good luck, have fun,

    Pat
     
  7. LynneP

    LynneP Chillin' With My Peeps

    It's been a long time since I saw douglas fir, out in British Columbia, and I remember a brother-in-law extolling it's properties. Your project made me nostalgic and I ended up here:
    http://www.softwood.org/douglas fir web/edougfir/EN/PGSA.htm

    The cost is prohibitive here, as you can imagine, but it's a lovely wood for construction. Lucky chooks!

    I hear you concerning wind, we're at the top of the Rawdon Hills in central Nova Scotia and we certainly get hammered by it regularly.
    We also built stronger than some folks would choose, but we know our coop and run will last. We added hurricane hangers where each joist on the run roof joined the structure- this can be done after construction, too, provided the area is not blocked with wire or other hardware. Shown in the link below.
    I've been following your thread with delight...[​IMG][​IMG]
     
    Last edited: Jan 26, 2010
  8. Chieftain

    Chieftain Chillin' With My Peeps

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    Let me correct my less than accurate language.

    Doug fir is more rot resistant than other materials as long as it is not in ground contact. If it is protected from the weather properly (and mine is) it will not rot out in my lifetime. I am in the process of protecting it with stain, and the entire rood framing is completely protected by the roofing itself.

    Carriage bolt s/b lag screw.

    Again, the ends of my posts, especially the top ends, are preserved, and driving a lag screw deeply and firmly into the end grain is extremely strong. There is no way for water to infiltrate those joints because they are up underneath the roof. Yes, those six bolts do a lot of work, but I believe they are up to it. More steel strapping is certainly an option and I will take a hard look at that, but the four posts that form the coop are structurally tied to both overhead beams with construction screws and there is no way that is going to tear apart in a few years from just the prevailing winds here.

    In addition, the roof slopes toward the prevailing wind, so there is down pressure on the whole roof, and it has not caught an updraft yet, in large part because those beams block the wind from getting underneath the structure.

    I understand your concerns Pat, but I have not found any weakness in this design yet, and I was on top of that roof daily while I was building it. It didn't even shudder with my 200 lbs on top of it, and as I mentioned we have had significant winds here ever since it went up.

    Sorry for the inaccuracies earlier, but I've been covering a lot of ground lately...

    [​IMG]
     
  9. patandchickens

    patandchickens Flock Mistress

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    All I'm saying is that rigidity when brand spankin' new, esp. rigidity to downwards or sideways forces, is a whole big lot different than rigidity after 5 years and to LIFTING forces, which is whatcha get from storm winds. Screwing into end grain just cannot ever be a very strong situation. This is precisely WHY you do not see this design used for sheds -- the beams need some horizontal tying-on, be it pinning through a mortise and tenon joint or nailing horizontally into a recess cut into the post or nailing horizontally into the post with a scab supporting the beam also.

    I am not trying to bug you, I was just concerned that your labor not be wasted by a single weak link in the chain so to speak -- I was looking at your design because I am wanting to build something really clean-looking for the turkeys this summer (without props or fasteners visible, with the appearance of mortise-and-tenon work except I do not have the time to invest in ACTUAL mortise-and-tenon craftsmanship [​IMG]), saw your design which has the aesthetic qualities I'm looking for, and was poring over your description to figure out how you got it to look that way [​IMG]

    Good luck, have fun,

    Pat
     
  10. SandyK

    SandyK Chillin' With My Peeps

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    Looks really good. As my husband would say, you could hang on it! Is there any reason you didn't use the metal corrugated instead? We used it on my shed porch sorta and it has held up great.

    Sandy
     

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