Minimum height roofspars?

[WillemII]

Hi,
As I am still in the design stage of a lightweight TD, I do have a question:
The roof will be 3 mm (1/8") outside and inside, and insulated. Trailer will be 4' wide. However, I'm still undecided about the roof 'thickness': I believe 2" height for the spars is quite common, but does anyone have experience with less? Is 38 mm (1 1/2") still acceptable? How about even less than that? Structurally, the thicker the better, I know... I don't expect to go and sit on the roof

Willem

[Gage]

My spares are only 3/4" and then 3/4" foam board for installation. Makes for a strong sandwich construction.

[Woodbutcher]

I use 1"X1 1/2". My fear using 3/4" is there is limited strength in carrying a load. Take a 3/4 x 1 1/2 board and flex it in each direction and see what I mean. Over time the roof may begin to sag a little trapping water around your vent if you use one.

[terryjones1]

I used 3/4" W x 1" H x 78" roof spars spaced approximately 10" apart.
I used sandwitch contruction with 1/4" plywood.
The roof is very strong.
It supports my weight (225 lbs).

[Lgboro]

I'm with Gage on this one.....I biscuit joined and dowel pinned 3/4 inch cedar to form a T for all my framing (ceiling,walls, and floor) and built in a sandwich with 1 1/2 inches of foam. If I were building I would build with 1/2 inch cedar and still feel very confident that I would have a more than adequate frame. The interior is sub 1/8 inch cedar strip and I floated my aluminum over the foam and frame much like Madjack and many others have. If i survive the "cedar lung" from this build I may build my son one with 1/2 inch framing.

I'm hoping the weight is low enough to be worth the extra effort and time, but at any rate, I know my tear is quite capable of being towed anywhere I should want to go.

[jdarkoregon]

I did the 3/4 X 1.5 plus some artsfartsy nonsense to give it even more strength, A total waste of energy.

Either way you go, there is less than an inch difference. Both ways are enough.

The way Gage did it gives you more surface area to glue the top ply, which is good. The way I did it has more structual strength, The insulation sandwich is where you will really gain a more rigid strength.

Just choose a way, go for it, you won't be unhappy. BOTH methods will be more than you need.

John

[Gage]

I use 1"X1 1/2". My fear using 3/4" is there is limited strength in carrying a load. Take a 3/4 x 1 1/2 board and flex it in each direction and see what I mean. Over time the roof may begin to sag a little trapping water around your vent if you use one.

I can see you know nothing about stress engineering or sandwich construction. Yep, that 3/4 x 1 1/2 board by itself will flex. BUT do a sandwich construction like I suggested above and try and flex it. Heck, I bet you even skinned your teardrop with 1/4" ply, which 1/8" is good enough when doing sandwich construction, and a lot stronger. Plus your dealing with an arc, not a flat.

[KCStudly]

If i survive the "cedar lung" from this build...

One word, "respirator". Just do it.

[Woodbutcher]

I use 1"X1 1/2". My fear using 3/4" is there is limited strength in carrying a load. Take a 3/4 x 1 1/2 board and flex it in each direction and see what I mean. Over time the roof may begin to sag a little trapping water around your vent if you use one.

I can see you know nothing about stress engineering or sandwich construction. Yep, that 3/4 x 1 1/2 board by itself will flex. BUT do a sandwich construction like I suggested above and try and flex it. Heck, I bet you even skinned your teardrop with 1/4" ply, which 1/8" is good enough when doing sandwich construction, and a lot stronger. Plus your dealing with an arc, not a flat.

You always know the nicest way to answer someones question. Every pancake has two sides. I did not insult you sir I offered a different perspective. My opinion was based on the fact that most home builders have limited experience. That is the reason they are asking questions here. If a sandwich construction is not done right it will fail. So rather then chance that I offered a safer alternative with the only down side being a loss of 3/4" inside and a plus of being able to use 1 1/2" ridged foam insulation.

Gage you have a nice day, I wish you well.

[Gage]

It's the pits being straight forward; someone is bound to be offended no matter how you put it. Sorry I hurt your feelings. I spent all day yesterday in the hospital, maybe I should have stayed off the board.

[aggie79]

To show you how crazy I was, my completely flat floor is 1x2 framing laid flat with 1/4" plywood skins yet my curved roof framing is 1x2 on edge with 1/8" plywood skins. The roof assembly is stronger than the floor assembly even though it didn't need to be.