Need some guidance on sandwich walls with foam as skeleton

[Sara-TNT]

I am thinking of using a sandwiched wall with 1/4 okoume on the outside (will extend to cover sides of floor) and 1 inch xps foam in the middle, with 1/8 inch Baltic birch on the inside. Foam and 1/8 inch will sit on floor.

I will use poplar framing around the doors.

The 1" foam will be the shelf for the spars (following Tony Lathans book but using foam for the skeleton).

Will glue be enough to hold walls to floor. I was thinking I should put a layer of wood trim around the bottom of the walls on the inside of the trailer.

Is this going to be too flimsy?

 

[pchast]

The wall should be stiff enough. You may need a stronger attachment to the floor IMHO. Screws?

 

[QueticoBill]

I have been thinking very similar. I was planning on attaching a 1x1 to edge of floor - screws and glue - and leaving foam and inch short at bottom. Set wall on 1x1 rib with glue and maybe a few small finish nails. I think the overlap with floor and the rib will be sufficient.

 

[GTS225-TNT]

The 1" foam will be the shelf for the spars (following Tony Lathans book but using foam for the skeleton).

Sara; Please clarify this portion of your post. I interpret it as saying the only wood framework will be around the door, leaving the entire wall to be foam. Seems to me you'll need a "skeleton" of wood of some type for any real strength.

Roger

 

[Sara-TNT]

Thanks for the question...yes, I was thinking of only using the foam, outside of the door frame for the skeleton. I was trying to reduce the weight of Tony's design...but I don't want to jeopardize structural integrity. I think I will talk to the lumber yard about the lightest wood I can use for the skeleton. Thank you.

 

[GTS225-TNT]

OK....but know this. I tend to "over-engineer" things when I build, so I could be fulla-crap. I'll defer to those that have already built out of foam, as there might be a method that works, and keep it a high percentage of foam like you want to do.

There is a wood that has good weight-to-strength. It's called Sitka Spruce, and is used quite frequently in the home-built airplane community. BUT.....it's pricey as wood goes.

Roger

 

[QueticoBill]

Sara; Please clarify this portion of your post. I interpret it as saying the only wood framework will be around the door, leaving the entire wall to be foam. Seems to me you'll need a "skeleton" of wood of some type for any real strength.

Roger

With good foam to ply skin adhesion, you don't need other internal framing.

 

[GTS225-TNT]

With good foam to ply skin adhesion, you don't need other internal framing.

OK.....I stand, (well, sit actually), corrected.

Roger

 

[Woodbutcher-TNT]

This is how I build my frames. The little extra wood usd in framing is well worth the extra support.

 

[reaver]

This is how I build my frames. The little extra wood usd in framing is well worth the extra support.

This is how I would do it. Create the skeleton, and fill all the voids with xps foam. Attach the skeleton at the base to the floor. This will be considerably stronger than gluing foam to the floor as your primary attachment method. Weight difference will be minimal, and you're not going to notice a difference in the insulation value between 3/4 in foam and 1 inch foam.

 

[Tony Latham]

I am thinking of using a sandwiched wall with 1/4 okoume on the outside (will extend to cover sides of floor) and 1 inch xps foam in the middle, with 1/8 inch Baltic birch on the inside. Foam and 1/8 inch will sit on floor.

Sara:

If you go down this road, I think you'll be creating a lot of issues to save 15-20 pounds.

How will you attach the headliner to the foam? How will you attach the walls to the floor? How will you attach or frame out the doors? How will you join the bulkheads? And of course, that's not touching on the challenge of attaching the sheathing to the foam.

The list is long, all for 15-20 pounds.

Tony

 

[S. Heisley]

" I think I will talk to the lumber yard about the lightest wood I can use for the skeleton."

I weighed every piece of wood that I used in my build and found that the weight of the wood can vary even within the same species. I found that Poplar was the lightest wood with the least knots and blemishes, but even then, the weight could vary. Wood that is lighter in color is usually lighter in weight. Especially, don't buy any wood that is still tinged with green. When available, Poplar is often what carpenters use for the framework of cabinets.

 

[Sara-TNT]

Thanks everyone!

 

[McFish1951]

I am thinking of using a sandwiched wall with 1/4 okoume on the outside (will extend to cover sides of floor) and 1 inch xps foam in the middle, with 1/8 inch Baltic birch on the inside. Foam and 1/8 inch will sit on floor.

I will use poplar framing around the doors.

The 1" foam will be the shelf for the spars (following Tony Lathans book but using foam for the skeleton).

Will glue be enough to hold walls to floor. I was thinking I should put a layer of wood trim around the bottom of the walls on the inside of the trailer.

Is this going to be too flimsy?

Review the techniques and strength of foamies in that section. Or see this video TeardropTrailers/comments/9pekq2/is_a_foam_trailer_strong_a_short_video_of_the_bug/

 

[Onajourney]

I am thinking of using a sandwiched wall with 1/4 okoume on the outside (will extend to cover sides of floor) and 1 inch xps foam in the middle, with 1/8 inch Baltic birch on the inside. Foam and 1/8 inch will sit on floor.

I will use poplar framing around the doors.

The 1" foam will be the shelf for the spars (following Tony Lathans book but using foam for the skeleton).

Will glue be enough to hold walls to floor. I was thinking I should put a layer of wood trim around the bottom of the walls on the inside of the trailer.

Is this going to be too flimsy?

Very happy with how I did mine. Very very sturdy, well insulated and super quite.

 

[Sara-TNT]

 

[Sara-TNT]

I started cutting the skeleton. I have not connected the smaller piece of plywood (30") on the front of the skeleton yet. My concern/question is that will the spline connection be strong enough since the spline connection will be in the the gap where the door will be. I bought a vintage technology door that is 30" wide and 36" tall.

I have not fully cut out the door opening. 3" of the opening will be on the extra 30" ply that I will attach to the 4x8.

I think it will be ok because the hinges will be on the 30" piece surrounded by 4" of solid wood from floor to ceiling.

 

[Tony Latham]

My concern/question is that will the spline connection be strong enough since the spline connection will be in the the gap where the door will be.

I think so. Ideally, the plywood is joined where the joint can run the full length of the sheet, of course.

Tony