Double roofs?

[Gnaatz1]

I was thinking of shoring up my roof (Plans) by using a single 1/8" layer, then putting a layer of Grace Ice and water shield down, then placing another 1/8" layer of plywood on her...Just trying to shore it up to be able to carry something like a canoe on the roof.

I am planning on building a larger teardrop. One 6'3" wide by 12 feet long, cabin will hold a Queen bed longways and 40" foldout bunk sideways, hence the 6'3" width.

I want to insulate, best I can, the floor, both walls and ceiling.

Any thoughts or comments are very welcome...

Gnaatz1

[Forrest747]

Well that should be enough the 1/8th and then another 1/8th, just offset teh seams. what are your plans for spars 1x2 should be enough for a 6'3" span. I wouldnt worry about adding the water proffing between layers. what is your profile going to be like.

[Greg M]

I don't think the water and ice shield between the layers is worth it. In fact it would probably make the roof weaker. The strength in a multi ply material is in the large sheer bond that stops each ply from sliding against the others when a bending force is applied. If the water and ice shield doesn't glue the two layers together firmly then they aren't able to reinforce each other and the roof's overall carrying capacity will be lessened. The strongest solution would be to glue the two layers of ply together with the water and ice shield on top and your finish material over all.
Hope that made sense

-Greg

[eamarquardt]

I don't think the water and ice shield between the layers is worth it. In fact it would probably make the roof weaker. The strength in a multi ply material is in the large sheer bond that stops each ply from sliding against the others when a bending force is applied. If the water and ice shield doesn't glue the two layers together firmly then they aren't able to reinforce each other and the roof's overall carrying capacity will be lessened. The strongest solution would be to glue the two layers of ply together with the water and ice shield on top and your finish material over all.
Hope that made sense

-Greg

Even better would be to separate the two 1/8" layers of ply with spars. This would result in an I-Beam like structure and would be both lightweight and strong. Hollow core doors are made this way and they are very stiff for their weight. Filling in the void with insulation would be easy and effective.

Hope this helps.

Cheers,

Gus

[bobhenry]

Even better would be to separate the two 1/8" layers of ply with spars. This would result in an I-Beam like structure and would be both lightweight and strong. Hollow core doors are made this way and they are very stiff for their weight. Filling in the void with insulation would be easy and effective.

Hope this helps.

Cheers,

Gus

I have to agree with Gus When I built the little 4x7 I only used 2 laters of pebble grained FRP panel I installed the inner ceiling attaching it to the 2x2 spars that were 12" o/c. I went outside and installed 2 layers of 3/4 foam in the voids between the spars. I then taped the foam to the spars and overlapped the osb sides for waterproofing.



I installed the roof with rosettes sealed with 100% silicone



And the end product weighed in at 535 pounds ready to sleep !



Even tested to 10 degrees and a brisk wind it was 78 inside with a tiny ceramic heater



The chuckwagon was not insulated but recieved only the FRP roof attached again with rosettes



Yes that is 1/2 of a concrete block filled with cement holding down the tarp
( the hatch was not on yet)



The rack was off of a jeep and very easy to cut down and attaches AT the spars.

Here we are showing off for the CRA Gathering

[Greg M]

Yes, building a torsion box roof creates a very stiff structure, but I'm not sure that's what the OP's question was about. I thought he was after putting a load (canoe) directly on the roof.
A single piece of 1/8 ply doesn't have a lot of point load strength. To use the hollow core door example: you can't bend it without a lot of force, but you can knock a hole in it quite easily. Now, if you wanted a roof rack, you could attach it to the spars, and not have to worry about strengthening the roof membrane. Light and strong

-Greg

[bobhenry]

Well Slow if ya had trees you could use one of these.







on a roofing note with a single ply see thru lexan roof inside temp went from 34 to 78 in 12 minutes.

How many BTU are there in a good dry meadow muffin