Cross Beams or Ribs Question

[Nitetimes]

Eh, I posted to this when the board went down then it got lost. I'll make a short version:

Argeed with Arne, you don't need a super duper roof.

Put spars wide side down for 3 reasons:
1. easier to hit with the brad nailer (like Arne)
2. easier to butt plywood on a spar
3. more surface area for glue

Yep, all of those 'cept I ripped cheap 2x2's for mine. Two layers of ply with a board between however thick is more than sufficient.

[cracker39]

I agree with Rich. I bought 10' 2x6s and ripped my 5' spars from them as all were 1" or more wide by 1 1/2" thick, and quite a few that were ripped at angles were even wider.

[halfdome, Danny]

I used 1" x 1 3/4" popular spaced about every 12", 1 3/4" rigid foam with 2 layers of Baltic Birch covered with .040 aluminum on a 5' wide TD. I have been on my knees on the roof while installing the fantastic fan with no deflection whatsoever. Danny

[Loader]

I used 1" x 1 3/4" popular spaced about every 12", 1 3/4" rigid foam with 2 layers of Baltic Birch covered with .040 aluminum on a 5' wide TD. I have been on my knees on the roof while installing the fantastic fan with no deflection whatsoever. Danny

Danny, is that what many would consider "overbuilt"? Sure it is very strong as you say indicate by the time you spent on top. Would a single 1/8 sheet be strong enough for the outer skin?

Time to use the search function I guess.

[halfdome, Danny]

I used 1" x 1 3/4" popular spaced about every 12", 1 3/4" rigid foam with 2 layers of Baltic Birch covered with .040 aluminum on a 5' wide TD. I have been on my knees on the roof while installing the fantastic fan with no deflection whatsoever. Danny

Danny, is that what many would consider "overbuilt"? Sure it is very strong as you say indicate by the time you spent on top. Would a single 1/8 sheet be strong enough for the outer skin?

Time to use the search function I guess.

I used 1X2 Poplar, face down (wide side) 12in on center. With 2 layers of 1/8 ply, it is plenty strong enough. I think Gage did his like that too.

Loader, You may consider it over built but the extra layer if 1/8" ply makes a very stiff form for very little weight gain. I would rather error in over building something than be dissapointed with a failure. Danny

[Loader]

Loader, You may consider it over built but the extra layer if 1/8" ply makes a very stiff form for very little weight gain. I would rather error in over building something than be dissapointed with a failure. Danny

I don't consider it overbuilt Danny. Agree, always error on the side of caution. I said some may, as you know, many threads on that subject. My question was, is a single layer of 1/8 outer strong enough. Of course it is over the 1.5 foam core, and another 1/8 inner skin. I have been searching the subject and find mixed reviews.

[Chris C]

Earl,

It's just an opinion, but I agree with Danny about "beams" being placed on 12" centers and two layers of 1/8" for the roof................whether planning on leaving the wood exposed or covering it with aluminum. Might be interesting to run a pole on the matter and see what people have done.........or plan on doing.

[cracker39]

A pole? You want a pole??? OK...I wasn't going to chime in anymore. BUT...since you asked....

My spars as described above, 12 inches apart, with 1 layer of 1/4" luan for skins. I think I could stand on the roof if I wanted to without any damage and very little bending. But, who is going to be standing on their roof? And if yor were going to, WHY? And, what else would be up there to bend it? I don't think that a couple of feet of snow on mine would bother it either...not that I live where there is any now.

You had to ask didn't you???

[asianflava]

I staggered each layer of ply so that it would cover the places where the bottom layer butted together.

[Arne]

I am toying with using full foam in the roof, and going with 1/8" ply on the exterior...

Has anyone used 1/8 instead of 1/4? Also, the roof would be fully curved, with the only flat area where the vent would mount.....

[Sonetpro]

I used 2 layers of 1/8" staggered seams. After the first layer I looked at it for strength, it was springy. It looked as if you put the aluminum on it, it would ding and dent easily. The second layer really stiffened it up. My spars are 12" on center in the radius and 18" on center on top.

[Jim Marshall]

I used 1X2 with 1/8 inch baltic birch inside and outside. I used .040 aluminum skin and I have had no problems at all. The roof is very stiff and it held my weight when I cut out the vent hole, without giving at all. I was very impressed with it's strength. I did use 2X2s for the vent framing. Here is a photo of my spars.

[Laredo]

Jim Marshall,
did that interior finish come on your ply for the sides, or is that fabric?

It looks so *fine*....

[Jim Marshall]

Laredo, it came on the plywood. They have it at Lowe's for about $18 a sheet. Thanks buddy.