Concave Curved Roofs

[chaddhamilton]

I'm building a 12x 8 shed on some property my wife and I recently purchased.  I've been thinking...rather, dreaming about putting a curved roof on it.  I haven't been able to find much info about how to go about it, nor have I seen firsthand the interior details of a completed roof.  

I found an image online showing a cross section view of such a desgn(I wouldn't want that much pitch):


My initial thought was that once I have the walls up, I could use a peice of plywood to make a rafter template from.  Then take that home to my woodshop and trace my template onto sheets of  3/4" OSB. Cut these, and then laminate them together for a ~ 1 1/2" rafter.    I've rough drafted this on paper and estimate the rafter length to be under 8'.

What says ye?  I'd love some comments, criticism and suggestions.

[archangel]

Possibly intended to avoid any type of snow load?

Also looks like it might creek loudly and would need to be secured well in an area with high winds.

[PEG688]

  I'd suggest 1 1/8" CDX plywood for your rafters.

  You'll more than likely need to screw the sheathing on to get it to suck down tight. Find a screw with a large head , about the size of  roofing nail , so the heads don't just pull thru the sheathing.

I'd also glue the sheathing to the rafter , and nail it off agian with big  headed nails, the screw would really be acting as clamps to suck the sheathing down.

  Inside you could use a collar tie similar to a "normal" roof of this size.

  Would you be intending to finish the interior? Like with drywall , or paneling.

   

[chaddhamilton]

Peg, the plans are for just a standard equipment/garden shed.   I was just wondering what you would reccommend for rafter spacing.   This is in the upstate of South Carolina where snow load is not an issue.

[MushCreek]

I wouldn't go more than 24" spacing to be sure the sheathing has enough support. I don't think OSB will hold fastenings well enough for that kind of application. Even plywood is iffy fastening into the end grain. I would either splice together 2X material, using glued and screwed plywood gussets, or if you really want to be different, make a form, and laminate 1X2's, gluing enough of them together to reach the desired strength and size. That would be real strong, and a definite conversation piece.

Where abouts are you in the upstate? Our property is about 5 miles north of Travelers Rest, almost to Tigerville.

[chaddhamilton]

Jay, we're off 11 at Table Rock State Park by the old CCC camp.   We talked earlier this year.  I have a road in and the building site is leveled and cleared.  Before I start on the 16x28 little house(next spring), I am putting this shed up to store my less-valuables.

I'll think about your 1x2' tip.  that might be the ticket.

[JRR]

If you take the shape the other direction ... "convex" .. or, more conventionally, "bowed" roofs ... you can find a good bit of building info on-line.

[MushCreek]

Jay, we're off 11 at Table Rock State Park by the old CCC camp.   We talked earlier this year.  I have a road in and the building site is leveled and cleared.  Before I start on the 16x28 little house(next spring), I am putting this shed up to store my less-valuables.

I'll think about your 1x2' tip.  that might be the ticket.

Now I remember chatting with you- I get 'CRS' once in a while!

[firefox]

Crazy idea here, butI was thinking that if the top is made of thick plywood, you could bond it at the top and spread it out at the bottom and that would be plenty strong. So I threw together some thoughs along these lines and came up with a doodle.
Most of it should be obvious, but if there is any real interest I will supply more details.

Drawing is at http://www.eecs.berkeley.edu/~bruce/Temp/roof-concave.jpg

The top section would also be carriage bolted to the bottom section.

If it were me I would use galvanized sheet metal to cover the plywood with 30# felt underneath.
horrizontal strips. Fold the top piece in half so that it covers the peak. Start at the bottom like you would
with shingles and nail so that the next piece conceals the nails. Where you need to secure the pieces together
without nailing, use 3M VHB tape.

The side bottom sections are semetrical  and can be made on the ground and lifted into place as an assembly
which makes this a candidate for ease of movement at a later time. Note all 45 deg corners.

[PEG688]

Peg, the plans are for just a standard equipment/garden shed.   I was just wondering what you would reccommend for rafter spacing.   This is in the upstate of South Carolina where snow load is not an issue.

I'd go 16 OC mainly due to the fact you'll need to get the sheathing to bend , closer spacing = more fasteners to pull it down.

  OSB might be a better choice or two layers to 3/8 CDX depending on the arch you cut.

  The two layers would be for mass / thickness to hold the roofing nails.


G/L PEG

Sorry for the slow reply ,  I sort of lost track of this thread.   

[chaddhamilton]

Bruce, thanks for taking the time to make that drawing.  I think I found just the perfect roof(and good illustrations to boot). With this pitch, I think rafters could be cut from 2x12's or even 2x10's.  I gotta draw it up tonight on paper and see.

It would really go a long way to add a little character to an otherwise boring storage shed...

[firefox]

That looks very nice!
Bruce

[MushCreek]

If you're careful selecting 2X4's at Home Depot, you could probably end up with a roof like that- without trying! (j/k)

[firefox]

Good point
You might be able to get a bunch of 2x4's and band them together tightly,
secure one end to a table or some such, then secure the other end so that there
is a constant tension on it pulling the ends down evenly. Then hose it down with water.
Ever so often increase the tension. Should work if done carefully with attention to detail.
Bruce

[Don_P]

That last pic made me think of a scissor truss with a curved "haunch" applied to it's top edge tangent to the slopes. The pitches could vary as could the size of the haunch to fair the curve if desired. It could be sheathed with 1x t&g.

[flyingvan]

http://countryplans.com/smf/index.php?topic=11822.msg151946#msg151946

   Here's a bit on curved rafters....