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Mushroom Man
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# Posted: 22 Apr 2017 12:02pm - Edited by: Mushroom Man
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I am looking to start 'designing' my gambrel roof.
I was going to use the traditional OSB for gussets to tie the rafters together. However, wont the OSB be in the way when I lay the wall/ceiling panels? Should I look into 'Nail plates' since I can maneuver those out of the way for my panels?
Will it be equally as strong either way?
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bldginsp
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# Posted: 22 Apr 2017 12:05pm
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Don't see what you mean. Got a drawing?
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Mushroom Man
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# Posted: 22 Apr 2017 12:11pm
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See in original thread bldginsp (just edited). 
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Bexeler
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# Posted: 22 Apr 2017 06:05pm
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I used OSB for the gussets. I then cut and attached boards to give me something to nail the interior sheeting to. You should be able to see in this pic.
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Mushroom Man
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# Posted: 22 Apr 2017 06:12pm - Edited by: Mushroom Man
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Bexeler Did you use trim on the bends?
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Mushroom Man
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# Posted: 22 Apr 2017 06:18pm
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Well the integrity of the gambrel roof be less if I would 'shape' the gussets to the same shape as the trellises?
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Bexeler
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# Posted: 22 Apr 2017 06:21pm
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I have not got that far yet what you see in the pic is as far as I am. This is just going to be a sleeping loft and I'm planning on using plywood for the sheeting. I'm not sure if I am going to use trim on the bends or not it depends on how the pieces match up.
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Mushroom Man
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# Posted: 22 Apr 2017 06:23pm
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Thanks Bexeler
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Bexeler
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# Posted: 22 Apr 2017 06:27pm
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Here is a pic of a shed that I finished the same way but with 1/4" OSB instead of plywood sheeting. I didn't use trim in here since it's is just a 8x12 she'd I'm using a mini cabin until the one I'm working on is done. If there is a gap in the new loft like there is here I will put trim on it.
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Bexeler
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# Posted: 22 Apr 2017 06:28pm
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Sorry about pics being sideways when I post from my phone they end up sideways.
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Mushroom Man
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# Posted: 22 Apr 2017 06:29pm
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Oh...I get it Bexeler! Nah...I can understand the pictures..np. That really helps. Thanks!
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Bexeler
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# Posted: 22 Apr 2017 06:39pm
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Glad I could help I will post pics on my thread when I get the plywood up.
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Spud
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# Posted: 22 Apr 2017 09:51pm
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This post does not have anything to do with regarding your question but as for designing your trusses you may find this link helpful.
http://www.blocklayer.com/roof/gambreleng.aspx
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bldginsp
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# Posted: 22 Apr 2017 10:08pm
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Mushroom- shaping the plywood gussets may reduce their strength, depending on the design. The gussets may do more than just connect the rafters as with nail plates, they may also be needed to resist hinging, again, depending on design. I like Bexeler's idea of putting on additional pieces next to the gussets to nail the interior material to.
Remember you need cross ventilation above the insulation.
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razmichael
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# Posted: 23 Apr 2017 06:27pm
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You might want to read through this thread as well Gambrel Roof. used a gambrel roof using plywood gussets - used 3/4" so the two sides match the rafter thickness - and did not cut them - full triangles. Keep in mind that I used a Ridge Beam (not a ridge board) which substantially reduces the load and outward thrust issue. Biggest problem is then putting up a ceiling as each gusset will likely be slightly different. I took 2x4's, figured out the length and angle to cut each end to basically stick out past the biggest gusset providing a consistent nailing surface along the sides. Full disclosure - I have not yet finished the ceiling (although spray foam insulation has been done).
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OwenChristensen
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# Posted: 23 Apr 2017 07:01pm
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The joints are all compression joints, there is no real stress on them. Metal plates are fine. BUT, building a gambrel roof you are very likely to push and bend it, until the sheathing is on. Make sure to stagger all your joints for strength. I put my top sheets on first without any weight on the roof, from a step ladder on top he loft floor. Push prop up , lift any rafter set that doesn't line up, until it does , before you nail the sheathing.
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ICC
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# Posted: 23 Apr 2017 08:22pm - Edited by: ICC
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Quoting: OwenChristensen The joints are all compression joints, there is no real stress on them.
Not quite. While there are some compression forces at work, each connection is also a hinge joint. A weight on the top of a vertical wall stud is under compression, but any member at an angle has more complex forces acting on it. Join two members at angles with vertical loads such as snow or even just the weight of the materials themselves and things get more complex. Each of those joints where a pair of wood or metal plates sandwich the cut ends of the rafter sections is a potential pivot or hinge. When winds blow against the side of a gambrel roof forces are transmitted to those splices. The unbraced gambrel roof is unstable compared to a properly constructed gable rafter roof with rafter ties at the wall stud tops.
Gable rafters plus rafter ties produce a triangle. A triangle is inherently stable, resists deformation by outside forces. The unbraced gambrel roof produces an irregular pentagon with no built in stability. The stability of the unbraced gambrel shape is provided strictly by mechanical means at each joint.
Get some popsicle sticks to simulate 2x's. Layout a triangle and a gambrel shape. Insert a few pins and then apply sideways pressure on the triangle and the gambrel pentagon. You can lock the triangle with a single pin or thumtack at each corner. The gambrel shape with a single pin is very loosey-goosey and deforms readily, falls down. The gambrel pentagon requires multiple pins at each joint to maintain the gambrel shape. That shape is held solely by the pin connections. If the wood member develops a split all strength at that pin is lost. Ditto for nails in a real 2x roof.
BUT, building a gambrel roof you are very likely to push and bend it, until the sheathing is on.
Isn't that alone enough to cause some uneasiness? Unstable even with sheathing on the roof. Sheathing may prevent distortion in the direction perpendicular to the vertical rafters, forces being applied against an end wall for example.But sheathing does nothing to reinforce against wind force against the side of the roof or the weight of snow on the upper, more horizontal surfaces. Those forces are being restrained by the mechanical connections where one rafter section meets another.
The main saving grace with these roofs on small sheds is the small size of the structure which reduces the total forces at play.
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ICC
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# Posted: 23 Apr 2017 09:02pm - Edited by: ICC
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If I wanted to build my own gambrel roofed shed, I would not use nail plates. Plywood plates would be vastly superior as they can be larger and spread the forces out over more rafter length, and I'd probably use 3/4" thick material. But for the reasons above I really don't like DIY gambrel trusses.
BTW, the plates used in factory built sheds and the plates used by manufacturers of factory built trusses of all shapes are NOT nail plates. They are quite different and have dozens of points that are pressed into the wood under great pressure. They are sized according to engineer calculations for the local snow and wind loads.
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toyota_mdt_tech
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# Posted: 23 Apr 2017 10:35pm
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Plywood, NO OSB, hate the stuff.
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morock
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# Posted: 24 Apr 2017 07:56am
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I'm with toyota, plywood only. I had an inspector in Ontario tell me plywood only as he would not pass a job done with an OSB gussets. Just an FYI.
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Cowracer
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# Posted: 24 Apr 2017 10:44am
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Nail plates take a bit of pressure to embed. I worked for MiTek inc for 8 years making roof truss equipment. Our tk-8 clincher would do at a max an 8" x 8" plate and it made 15 tons of force.
Here is a video of one in action, and bear in mind that they would routinely break that big aluminum c-frame after a few thousand presses.
URL
I have heard of guys using a "potato masher" tamper on a concrete floor doing it by hand, but that is the absolute minimum. If you do not do it on a super firm surface like the afore mention concrete floor you will not get good embedding of the teeth. You cannot do it on dirt or a wooden subfloor, and you cant beat them in with a hammer.
I used plywood for mine just so I know they are secure.
Tim
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ICC
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# Posted: 24 Apr 2017 03:05pm
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The Mitek connectors are the type that truss factories use. As stated above they need a big press for installation, not for hammers.
I believe the OP was meaning to use a metal plate with pre punched holes like the Simpson TP and TPAplates. Simpson does not rate these for any loads. They are not meant for structural uses. They are a nail on version of their MP, mending plates, that look more like the Mitek connectors. However on the MP plates Simpson stamps "not for trusses" right on them. We're really on our own if we build trusses by hand.
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Cowracer
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# Posted: 24 Apr 2017 04:26pm
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One thing I forgot to mention...
To the OP; Yes, if you use plywood or osb, you will have to notch the plywood for drywall clearance.
Here is a picture of mine as we were building:
If you look closely in the corners, you can see where the plywood 'plates' hung over the edges of the boards. 10 minutes with a sawzall fixed that right up
Tim
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OwenChristensen
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# Posted: 27 Apr 2017 08:38am
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While I do agree that over sized plywood plates are the best and it would be nice if the roof did not distort while sheathing, after building about one hundred gambrel sheds with lofts, I find they are very strong and if the roof plywood is staggered, and if you adjust the rafters to be where they are supposed to be, the roof will support huge wind stress and snow load. It is an art to put one together properly.
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Ushuaya
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# Posted: 26 Apr 2021 02:46pm
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Why not getting a professional to do that?
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Ushuaya
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# Posted: 26 Apr 2021 02:47pm
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Oh my, I didn't even see this post is so old 
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Landore
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# Posted: 26 Apr 2021 02:50pm
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It's kinda complicated when it comes to tieing the rafters together. In general, I wouldn't start to plan something such complicated. Or maybe I'm like this, idk.
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Brettny
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# Posted: 27 Apr 2021 05:29am
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These gambrel roofs arnt that complicated and blocklayer.com has a really good calculator for them. They tell you every angle, length and even gusset size. After knowing all that it's just a matter of reading a tape measure, cutting the wood and screwing things together.
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