Dumb framing/ 'sandwich wall' construction question....

[Changer]

I've gone back to the drawing board (again - nothing better to do when you're too broke to start DOING stuff ) and am back on the "wanna build" bandwagon. I'm leaning towards a modified weekender (about halfway between the Weekender-weekender and the on eon Txstewartfamily's site) and I want framed walls to keep the weight down and have more places to put insulation.

Some of the designs I've seen that are framed have the sides made out of thicker plywood with sections cut out to reduce weight and then are 'skinned' with stuff on the inside and outside. Is this the most efficient, or would it work better to build a frame, fill with insulation, and skin the inside and outside? Which is easier for a novice builder? What dimension of wood do you want for the framing, if it's NOT cut-out plywood? Assuming you're skinning over a frame, rather than over a solid piece of plywood, what weight of wood (Leaning towards plywood with epoxy paint for the outside and ... I don't know what for the inside. Simple and cheap are keywords for this.

Thanks guys!
Cait

[angib]

Structurally, you need very little connecting the two skins. If you were making a sandwich wall with a 3/4" (nominal 1") gap, then 1x1 strips would be enough. You might want to use bigger framing, like where the door hinge screws on, but the sandwich panel doesn't need them.

You need to start thinking of this as a sandwich panel, and not the wall of a house. 'Building a frame' and then skinning it means you built the frame far too strong/heavy, as the frame never needs to stand up on its own.

Instead you take one skin and add framing to that - that combination should be strong enough to stand up on its own as there are good practical reasons for building from one-skin panels - such as being able to run wiring or add backing blocks to interior fittings, before you add the second (usually outer) skin.

Andrew

[starleen2]

If you’re looking for the least expensive way to build – then the framing method is probably the best. For instance if you are going to insulate with 3/4 foam insulation panels – then rip a 2x4 down into 3/4 widths thus doubling your material with little waste. I’ve also use some leftover ply to frame with as well. The whole sheet method by which most of the material is removed seems a little expensive to me – but is an efficient way to accomplish the same task. – Imagine No seams from the joints! These methods take in an account the strength of the plywood – not the framing, although the framing keeps the panels from warping and provide some structural stability to the panels.

[Changer]

Thanks guys! I knew 2x4 framing was overkill, but wasn't sure what WAS the right dimensions. I am theoretically going to have help on this project but suspect it's going to mostly end up being just me, so the more dumb questions I ask now, the fewer dumb mistakes I will (hopefully) make later.

[bobhenry]

An all 1x material frame is a bit daunting for a total novice with the radii and compound cuts and pocket screws and glueing.

I think the full sheet/sheets method is much more straight forward.

Find a few radii that make up the profile you like and simply cut it out.

When I built chubby I used 2 1/2 full sheets of 1/2" osb stood on end for each side.

I would have to check notes to give the exact radii but it was simply a long stinny board ripping and a nail at the pivot point and a hole drilled for a pencil to mark the cut line

Here is a 4x8 layout With refinements by Andrew
http://www.mikenchell.com/forums/viewtopic.php?p=180832&highlight=#180832

As Chubby is 5'6" tall and just under 10' long it took 3 different sheets The center sheet was narrowed to 43 inches so it would lap right on the door reinforcing post and the galley wall. The sheets were screwed and glued to the 1x4 underneath to join the two sheets



Here is the reinforcement at the door



In this framing side shot ....Notice I tied all 3 sheets together with the 1x4 bottom board running full length. The side sheets extend below the floor and are screwed and glued to the 2x4 ribbon at the edge of the frame so this 1x4 helps carry the weight of the wall to relieve the strain that would otherwise be on the fastners only



The 3/4 void is enough to wire the wall for electrical and I simply drilled 1/4 " holes thru the 1x4 where needed. These are hard to do with the outer sub skin on as the drill case get in the way a bit , so a little preplanning of these holes would make this step a bit simpler.

NOTE : try and group your electrical runs and make a mental note where they are, so should you brad nail on your inner skin you will not shoot fastners into your wiring !


After wiring fill with 3/4 blue foam board and skin the inside.

[aggie79]

Still working on my first teardrop, but if you're going to insulate the walls, I think the plywood "framing" route is the way to go.




Gig'em, Tom

[bbarry]

On my Kampster, I used 3/4" ply and cut out sections to create the "framing." After filling the voids with foamboard insulation, I then epoxied on 1/8" ply to both sides to end up with a 1" wall. I did have to biscuit on a small piece at the galley end because I couldn't get ply in 10' lengths.



As far as what would be "simple and cheap" as you say, I'd say you have a couple options.

1) Simplest: Just use 3/4" plywood, epoxy over and paint. You don't have to worry about stick framing, cutting out any plywood, or skinning any panels.

2) If you are dead-set on having an insulated wall, my choice would be to do it like I did. Although it is a waste of material, it makes for a strong wall without all the biscuiting and joining from a stick built wall.

Good luck!

Brad

[Changer]

I'm dead set on insulating. It's just too miserable here a lot of the year not to (and my biggest reason for wanting to get out of the tent is that I *hate* waking up with condensation on me and my bedding. )

I have not even started THINKING about electrical beyond "Battery powered?" I want a vented fan, I think, hooked up to that battery, a reading light, and a way to hook up to shore power for when it's available (with the intention of adding 110V AC later on), but I was thinking I'd just run all those things in a channel on top of the insulation+panelling?

I'm going back and forth on 'easier'. Would framing be significantly lighter?

I really wanted to go to the teardrop gathering yesterday to pick people's brains and got tied up with work. Hopefully the next one. I'm also still messing with sizes (it'll either be 5x8 or 6x8, but today I'm leaning towards 5x8 with a 'tilt-out' foot space so I can put the bed crosswise and have interior floorspace for cargo.....)

[asianflava]

I used 1X2 framing and 3/4 thick insulation, don't use furring strips because they aren't quite 3/4in. It was just plain ole pine, but I used poplar at the door hinge area. The inside and outside were skinned with 1/8in luan and 1/8in baltic birch.

[angib]

Although it is a waste of material, it makes for a strong wall without all the biscuiting and joining from a stick built wall.

Yes, but "all that biscuiting and jointing" is also a complete waste, once the two skins are in place. All the framing needs to do in a sandwich panel is to connect the two skins together. There is no need for the framing to stand up on its own- that's just a misunderstanding of what it's there for.

Andrew

[alffink]

Yes, Yes

as andrew is saying, don't think of the 1 x 2's or what ever you will eventually use, as frameing. they are merely spacers for the Foam and the cleats to hang your shelves on. They don't need bisuits or pocket screws etc.....now if you trying to go ultra lite and use 1/8" ply + 3/4" foam + 1/8" ply you may have to have a more substantial frame but I can't see that substantial of a weight savings to make all that extra work worth while, and just making the two walls indentical would be much more dificult for little gain.

Theoretically, you could just use 1/2" ply for the wall, attach 3/4" insulation and then 1/8" interior paneling, but then the paneling and foam does not make for a good mount for every thing your going to hang on the walls such as bulkheads and shelves.

Just my opinion, as has been mentioned a couple of times, this is just a stressed box not a house, try not to think of framing in the same way.

[Arne]

see the link at the bottom of this note.

[alffink]

Great build page Arne

I have similar photos in my build file, but not in my album

A good picture really is worth thousand words

[steve smoot]

Although it is a waste of material, it makes for a strong wall without all the biscuiting and joining from a stick built wall.

Yes, but "all that biscuiting and jointing" is also a complete waste, once the two skins are in place. All the framing needs to do in a sandwich panel is to connect the two skins together. There is no need for the framing to stand up on its own- that's just a misunderstanding of what it's there for.

Andrew

I think Andrew has the right idea. This is how I plan to build my walls, if and when I ever get the cash..

[Changer]

I'm not planning on putting much of anything in the way of shelves and bulkheads in- a nightstand (that will go over the future A/C if I don't use an RV roof type) and a platform for the bed - the rest is going to be open space for crates and storage bins.

Does that make a difference?