Roof Spar Joint - Alternatives to Butt Joint

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Re: Roof Spar Joint - Alternatives to Butt Joint

Postby noseoil » Sat Nov 19, 2016 9:42 am

Suggestion for QB, go to home center store. Look at hollow core doors. Ponder roof structures....

I'm thinking that a spar/skin roof with an inner & outer layer is simple, light, easily insulated, strong & works well structurally. The curved panels provide strength laterally, 1/8" plywood is strong & light. Granted, the foam insulation simply acts as a "web" in that it ends up being a simple, weak compression member, with no real ability to transfer loads, but in this application it really isn't necessary. In the flat sections, spars supply resistance to bending loads & axial forces are transmitted into the side panels, where they are distributed into the frame, eventually.

I guess my question would be, with the accumulated knowledge from builds spanning many years & empirical evidence to "support" it, why reinvent the wheel in this instance? Sure, there's plenty of room for innovation in a build, but putting legs on a snake has never been my idea of fun. I guess I spent too many years dealing with people who had vast amounts of education & theoretical knowledge, while all it ended up doing in most cases was to cost more in the end product & make a less efficient use of time for me at the computer.
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Re: Roof Spar Joint - Alternatives to Butt Joint

Postby QueticoBill » Sat Nov 19, 2016 11:53 am

noseoil wrote:Suggestion for QB, go to home center store. Look at hollow core doors. Ponder roof structures....

I'm thinking that a spar/skin roof with an inner & outer layer is simple, light, easily insulated, strong & works well structurally. The curved panels provide strength laterally, 1/8" plywood is strong & light. Granted, the foam insulation simply acts as a "web" in that it ends up being a simple, weak compression member, with no real ability to transfer loads, but in this application it really isn't necessary. In the flat sections, spars supply resistance to bending loads & axial forces are transmitted into the side panels, where they are distributed into the frame, eventually.

I guess my question would be, with the accumulated knowledge from builds spanning many years & empirical evidence to "support" it, why reinvent the wheel in this instance? Sure, there's plenty of room for innovation in a build, but putting legs on a snake has never been my idea of fun. I guess I spent too many years dealing with people who had vast amounts of education & theoretical knowledge, while all it ended up doing in most cases was to cost more in the end product & make a less efficient use of time for me at the computer.


The sparless roof with inner and outer skins, well supported by the foam and bond, should be strong, better insulated, light, and easier to build. This was a discussion about alternatives to attaching spars and omitting them is about as simple as it gets.

Your point about why change and develop new designs is simply not in my nature. Its leisure activity, not business, and doing research and development on my own dime that affects no one else. It's no different than going canoeing or backpacking where few or no one has gone before, or simply avoiding crowds. I appreciate you and all here sharing their experience and advice, but certainly a sparless roof is not even as radical as an all foam, glue, and canvas roof - my hats off to that crowd as I don't have the courage - and - if I can find the right adhesive - should be easier, lighter, and structurally much more than acceptable. Besides, in my work I've designed many similar stressed skin pieces for very different applications and it's worked fine. The only difference is the panels were built in a factory with some specialize gluing equipment and expertise, but a lot of that was designed for people to walk and jump and dance on, so finding a glue system that I can do in my garage that will work for the minimal live loads of a TD roof is my only challenge.
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