Wall Construction

[lacofdfireman]

What's RTT?

I also wonder at the weight savings of skeleton and then having to add 1/8" skins on both sides.... that almost seems like zero weight savings.

(RTT) Rooftop Tent




Sent from my iPhone using Tapatalk

[Andrew Herrick]

Also I figured if I used a solid sheet of 1/2-3/4” that would be plenty of insulation?

I'm one of those odd people who become excited over such mundane topics as thermal insulation. So with that said …

Insulation serves two purposes: acoustic and thermal resistance. If you're talking a 1/2-inch to 3/4-inch of plywood as sufficient insulation, then I would argue the answer is a resounding NO. This is for many different reasons, but a big one is that controlling air temperature is only half the battle. In small campers, controlling the temperature of the walls and ceiling is of equal importance due to all the radiant heat in such a small space.

So I would argue that some form of thermal insulation should ALWAYS be specified. Even something as simple as carpet or foam-backed vinyl on the interior walls will make the camper FEEL much cooler on a hot day. Many fiberglass "eggshell" campers have done this for years.

Obviously, as has been pointed out, vintage campers made do with 1/2-inch plywood walls. So do you need insulation? No. But there's no question that foam insulation makes the camper more comfortable and useful. After having built both construction styles, I would always recommend an insulated shell (minimum an insulated roof).

*Hopping off soapbox*

[Ottsville]

Also I figured if I used a solid sheet of 1/2-3/4” that would be plenty of insulation?


Sent from my iPhone using Tapatalk

build yourself a plywood box, let it sit in the sun all day, then go sit in it...
My guess is you'll find the wood transfers a surprising amount of heat.

I question the strength of just a 1/2" or even 3/4" wall to support the stress of a RTT on the roof while off-roading. Remember, we are talking about much more than just vertical load. Unless you are going to add some framing, and if you are going to add framing, then why not just go with 1/4"? Or even 1/8"?


I'm excited to see your build though. Your first one was pretty cool.

[lacofdfireman]

Also I figured if I used a solid sheet of 1/2-3/4” that would be plenty of insulation?


Sent from my iPhone using Tapatalk

build yourself a plywood box, let it sit in the sun all day, then go sit in it...
My guess is you'll find the wood transfers a surprising amount of heat.

I question the strength of just a 1/2" or even 3/4" wall to support the stress of a RTT on the roof while off-roading. Remember, we are talking about much more than just vertical load. Unless you are going to add some framing, and if you are going to add framing, then why not just go with 1/4"? Or even 1/8"?


I'm excited to see your build though. Your first one was pretty cool.

My last build I did 3/4” outer walls with 2x3 framed inner wall with a 1/8” inside wall. And 2” foam board insulation between the outer and inner walls. Was super insulated.

I think I’ve convinced myself to do this one with a 1/4”outer wall and a 2x3 inner wall and 1/8” inner wall and then I’ll also do the 2” insulation between the studs again. Should be sturdy enough to hold my RTT. Then I’ll do 1/2” roof so I can stand on it. Sound good?

[Ottsville]

That sounds reasonable. Strong, yet lighter than last build, which is what you were looking for.

[aggie79]

Also I figured if I used a solid sheet of 1/2-3/4” that would be plenty of insulation?


Sent from my iPhone using Tapatalk

It's hard to quantify "plenty". EPS has about three times the insulation value per thickness of plywood. XPS has about 3-1/2 times the value of plywood. Granted, stick framing is a thermal bridge, so you don't get the true value of insulation only.

Insulation does provide both thermal and acoustical insulation benefits.

[Jeepertrains]

TD Wall structure.jpg (26.97 KiB) Viewed 2103 times

This is the structure I'm considering using on my TD.
Has anyone tried this?

[Esteban]

homeconstructionimprovement.com/foam-board-insulation-values indicates that:
!) Expanded polystyrene foam (EPS) typically has an R value of 3.6 to 4.0 per inch of thickness.
2) Extruded polystyrene foam (XPS) typically has an R value of 4.5 to 5.0 per inch of thickness.
3) Polyisocyanurate (polyiso) often has a foil facing and typically has R values of 7.0 to 8.0 per inch of thickness.

My teardrop will be insulated with polyiso foam boards to achieve higher R values (which will be reduced by the wood framing):

Floor. The floor will have 3/4" thick polyiso in it. The floor's rigid foam R value will be about R 5.25 to R 6.0. I'll use 3/8" plywood for the top of the floor and 1/8" plywood on the bottom of the floor.

Walls. The cabin side walls will have 1" thick polyiso. The walls rigid foam R value will be about R 6.0 to R 8.0. I'll use 1/8" plywood inside and outside the cabin.
The bulkhead between the sleeping cabin and the galley will have 3/4" polyiso with a rigid foam R value of about R 5.25 to R 6.0. The bulkhead will have 1/8" plywood on both sides.

Roof. The roof and front wall will have 1-1/2" polyiso. The roof and front walls rigid foam R value will be about R 10.5 to R 12.0. I'll use 1/8" plywood for the cabin ceiling and the roof skin.

The outside of the teardrop will be fiberglassed (and painted) to add strength, rigidity and waterproofing.

[greygoos]

TD Wall structure.jpg

This is the structure I'm considering using on my TD.
Has anyone tried this?

Look at this build. He did the same if not similar to what you are asking about. viewtopic.php?f=50&t=66930

[QueticoBill]

I'm not keen on polyiso . By many reports it looses r value as it outgasses and ages. You might check https://buildingscience.com/documents/i ... nt-r-value

Its also seems hard to get a structural bond between foam and skin, if you plan on any strength from the composite panel. And it's always seemed a little more brittle and less able to bend.

[Ottsville]

I don't believe you can get polyiso without a facing of some sort, usually foil or tarpaper, so composite panels will be limited by the strength of that facing. Polyiso also absorbs water more readily than eps or xps. Performance of Polyiso also drops with temperature, and some builders in colder climates give it a lesser R value because of that.

[Andrew Herrick]

Also I figured if I used a solid sheet of 1/2-3/4” that would be plenty of insulation?


Sent from my iPhone using Tapatalk

Plywood and solid wood has an R-value (insulation effectiveness) of approximately 1 per inch. While much better than aluminum or steel, that's not much compared to any other insulation material, such as fiberglass strand, cellulose, mineral wool, EPS/XPS/Polyiso foam, spray polyurethane foam, etc., which boast R-values between 3.3 and 7.5 per inch. To put that into a perspective: Adding 1-inch of EPS insulation to a wall assembly reduces the conductive heat transfer about 5x. Denser forms of insulation may also help mitigate sound transmission, making for a quieter and more relaxing camper.

Yes, old school camper bodies were made with solid plywood. If you pay attention to building an airtight shell, this will retain heat decently. If you want something that stays comfortable in all seasons, though, and has a quieter interior, then you'll want insulation. You get what you pay for

[noseoil]

"I also wonder at the weight savings of skeleton and then having to add 1/8" skins on both sides.... that almost seems like zero weight savings." Sorry to get back to this comment so late, been a bit busy with the move.

3/4" plywood is about 1.91 pounds per square foot. 1/8" Baltic birch is about .44 pounds per square foot. If you look at a Benroy that is 4' tall X 9' long (like we made), the original 3/4" sheet-weight is about 85 pounds before cutting, due to the type of exterior plywood used & the added foot of length. The Baltic birch weight is about 31# for both sides before any trimming, door cut-outs, etc. Once you remove most of the 3/4" plywood to make the skeleton, whittle out the doors & windows, trim the curves & remove the extras, it's much less weight, stronger & easier to insulate.

Here's the skeleton panel, trimmed of excess weight it tips the scales at 17#, quite a bit less than the original one. It's actually about half the weight of a solid panel, with the two 1/8" skins attached & finish applied & sealed. Could it be less weight? Yes, less labor? Yes. Better for what we wanted? Nope!