Roof spars spacing

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Roof spars spacing

Postby bobwhite215 » Sun Dec 25, 2016 4:59 pm

Getting ready to put in my roof spars. Just curious how others have spaced them. I'm thinking about every 16" or so. Maybe a little closer around the front of my profile which has a little tighter bend. Thanks.

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Re: Roof spars spacing

Postby Tomterrific » Sun Dec 25, 2016 6:34 pm

I did 16" on center except at the bend in front where I used 8" on center. I used 1x2 flat and 3/4" insulation. At the hatch I used a 1x4 for the hinge. Along the edges i used gluded blocks after the ceiling was installed before the roof. I don't think it would be a bad idea to use tighter on center spacing but mine worked out okay on my very light weight build.

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Re: Roof spars spacing

Postby mikeschn » Mon Dec 26, 2016 6:03 am

I tried for about 12" centers, and a little closer if on a tight bends. Also, used 14 1/4" opening for the roof vent.

Look here, on page 16. http://www.mikenchell.com/images/GenericBenroyPlans.pdf

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Re: Roof spars spacing

Postby bobhenry » Mon Dec 26, 2016 8:32 am

For some reason I added a 2x6 where the roof was almost dead flat , as a spar. It turned out to be a blessing as I installed a handicap bar. It helps in setting up and moving about and has allowed me to suspend heaters and fans overhead as a temporary mount. It was a happy accident that have proven time and again to be a great feature. (for what it's worth )
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Re: Roof spars spacing

Postby daveesl77 » Mon Dec 26, 2016 8:53 am

Being the "belt/suspenders" guy, I overdid mine (as usual). 1.5" square spruce spars, spaced every 12" (maybe it was 8) plus 4 full width 1/4" all-thread tension rods. Spars push against the walls, rods pull them in. That said, I can stand on the top of my roof structure.

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Re: Roof spars spacing

Postby Dan242 » Mon Dec 26, 2016 11:56 pm

bobhenry wrote:For some reason I added a 2x6 where the roof was almost dead flat , as a spar. It turned out to be a blessing as I installed a handicap bar. It helps in setting up and moving about and has allowed me to suspend heaters and fans overhead as a temporary mount. It was a happy accident that have proven time and again to be a great feature. (for what it's worth )

I can see this as a great idea, thanks,
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Re: Roof spars spacing

Postby yrock87 » Tue Dec 27, 2016 1:05 pm

My roof only has 3 spars with over 24 inche gaps. but I also used a foam core bonded to the plywood skins for strength. I can sit on the roof now that it is complete. it all depends on your construction method. If bonding plywood skins to foam core you don't really need much as roof spars go. a more traditional stick built with a single skin would need closer spacing for the spars.
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Re: Roof spars spacing

Postby QueticoBill » Tue Dec 27, 2016 8:50 pm

1*2 or 2*2 spars or 1 1/2" foam will barely support themselves I've 5'. The ply skins do all the work, with spars or foam simply keeping them acting together. Is it harder to get a foam tonpky bond than wood spar to ply? Probably. I just think it's worth it. Partly no thermal bridging but largely engineering "elegance". My comfort level with all foam core is based on a lot of experience with it in other applications (orchestra shells and portable platforms used in live entertainment). My problem is very little engineering data on less than 1/4" ply so 1/8" ply design is more instinct and guess.
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Re: Roof spars spacing

Postby KCStudly » Thu Dec 29, 2016 4:32 pm

I used a 5mm Okoume ply ceiling with 1-1/2 thk foam over a slightly arched roof profile (something like 572 inch radius, IIRC). What I found was that the ply would not support itself initially. Rather than buying a bunch of lumber to make temporary props or a form to allow the foam to be laminated onto the curved ceiling, or attempting to laminate the foam on and them bend it over the profile after the fact, I glued 1x2 spars (on edge) about 8 inches on center, plus 2x2's spaced 14-1/2 inches at the fan, installed that as an assembly all in one piece (ceiling skin with spars attached running from the galley bulkhead to the bottom of the front cabinet), and then infilled in between the spars with pieces of foam before skinning with epoxy and FG.

I was a bit picky about not letting the ceiling ply sag. Perhaps a more highly arched roof or thinner (lighter) ply wouldn't have sagged as much, but adding the spars seemed to be the path of least resistance for me at the time.
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Re: Roof spars spacing

Postby OP827 » Fri Dec 30, 2016 12:35 am

QueticoBill wrote:1*2 or 2*2 spars or 1 1/2" foam will barely support themselves I've 5'. The ply skins do all the work, with spars or foam simply keeping them acting together. Is it harder to get a foam tonpky bond than wood spar to ply? Probably. I just think it's worth it. Partly no thermal bridging but largely engineering "elegance". My comfort level with all foam core is based on a lot of experience with it in other applications (orchestra shells and portable platforms used in live entertainment). My problem is very little engineering data on less than 1/4" ply so 1/8" ply design is more instinct and guess.


I know that Glen from BC has built a 1/8" baltic birch plywood with 1" xps foam sandwich teardrop using his vacuum pump equipment and TBII. And it seems to work fine for his curved roof teardop with no roof spars.
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