Hello! I am in the midst of designing a Tiny House that will sit on a 26' trailer. Because I will need to pull the house behind a truck my #1 priority is to come up with the lightest construction technique possible. Some other requirements are as follows:

*100MPH wind ready - (due to 60pmh highway driving)
*Good moisture control (due to living in Portland, OR with >200 rainy days/yr)
*<=6" walls (each additional 1" reduces the living space substantially.)
*Easy construction technique (I'm a first time builder.)
*R-Value not a huge priority as energy savings come from small size of house (<3000 Cubic Feet)

So far I'm leaning towards the RayCore "SIP" panels (I know, I know - they're not really SIPs because of the studs.) What appeals to me about these panels is the ease of construction, the relatively thin panels (with their 4" model), and the (potential) ability to save a ton of weight by constructing without (heavy) side paneling. This leads me to my main question: Would it be possible to build a tiny, one story house using RayCore panels *without* fastening (heavy) OSB/Plywood panels to one or both sides? More specifically:

1: Could I skip fastening OSB/Plywood t the exterior and go straight from the RayCore panels to a water barrier and then house siding without completely compromising the structural stability and/or causing big moisture problems or a completely horrid overall R-Value?
2:Could I skip fastening a layer of OSB/Ply to the interior wall and go straight from the RayCore to wall panelling? (I won't be using gypsum as it is also prohibitively weighty.)

Again, I realize that these are not best practices and that I'm sacrificing a certain amount of R-value in building this way *but* without keeping my house lightweight I will not be able to "roll" and constructing without fastening OSB/ply to one - or both - sides of the wall would significantly cut down the weight of the house.

I very much thank you for your thoughts on this technique and/or alternatives that I may not have thought of yet!

Thanks!!! =Zach=

Ok, so I've done some research and answered some of my own rookie questions:

As far as structural stability goes it looks like using OSB just on the corners of the house will be sufficient. Perhaps even 1x4 let-in braces will be sufficient but the research looks tenuous as far as let-in braces in high wind areas (a given for me if I'm pulling my house at highway speeds.)

Overall what I'm thinking at this point is the following wall layers:

*RayCore boards with the seams taped together to create a vapor barrier.
*A housewrap as an additional vapor barrier (if an additional vapor barrier is necessary over the taped Raycore boards.)
*1/2" Furring strips on top of the studs in the RayCore Boards and 1/2" 4x8 OSB at the corners for structural stability.
*Vented rain screens between the furring strips as a moisture drain
*Siding nailed directly into the furring strips over the rain screens. (I'm not a big fan, but I'll probably be using Vinyl Siding as it's by far the lightest weight siding I can find.)

So is there anything I'm missing? Am I missing anything in regards to structural stability? Moisture Control (Remember I'l be living in Portland, OR so its wet, wet ,wet)? Are there any other lightweight construction techniques that I'm over-looking?

Thanks!!!
Zach

Plywood is lighter and generally more weather resistant than OSB. You could use a T1-11, 3/8" (11/32") plywood siding that would serve both your siding and structural purposes. Google T1-11 siding for more info.

Thank you, Arkie6! That suggestion saves me ~80# off my design if I'm using the ply instead of OSB for the corners - and every pound counts!

You can get SIP's made with T111 applied on one side and 7/16 OSB on the other.   Fisher makes them as does General Panel Corp.  probably others too. When you put them together make sure you paint all the edges to prevent moisture infiltration which could cause swelling/rot. Then assemble the panels and caulk the joints and paint with a good quality exterior paint.   This eliminates  extra weight, moisture barrier, and extra layer.  Gives you great insulation as well. another option would be to cover osb sips with an aluminum skin.  or galvalume roofing or siding which comes prepainted with 40+ year warranty.  Not as attractive but very lightweight and will last 2 lifetimes.

If you really want to go light, find a grocery store or reatuarant that is out of business and buy there old walk in cooler.  You can usually find them pretty cheap especially if the cooling unit no longer works which you won't need anyways. They are basically aluminum skinned sips. They are only about 2" thick and very light.

I assume you do not have to meet any specific codes as you are building on a trailer.

How about this as the core of your house? Strong. Weatherproof. Can be linked together.
http://www.brouwerbouwplaats.nl/custom/page/page_block/bouwbedrijf-de-waal-amesfoort_original.jpg

As with some boats and airplanes, I'd build the whole thing from foam and then put fiberglass/epoxy on both sides. Next best would be some type of aluminum skinned foam panels.