Target R values for surfaces?

aernan

Observer
Hi I'm new here. I've seen some discussions of materials for campers and I didn't want to resurrect threads from 2012.

For those of you who have built/upgraded expedition campers. What target R values are you going for for: Roof, Walls, Floor?

I have found some good recommendations for houses and here are the numbers:
I will post for regions 3 (California) and Region 7 which is cold places like Alaska


-------------- region 3 | region 7
Attic (roof) R30 to R60 | R49 to R60
Wall (cavity) R13 to R15 | R13 to R21
Floor ---------- R25 | R25 to R30
 

john61ct

Adventurer
Takes 4" of polyiso to get R-23

Need a big living space to be willing to give that up.

From extreme heat you really have to, boondocking with aircon, yuck.

But extreme cold can be easily overcome with an efficient heater.
 

aernan

Observer
Yeah looking at those numbers it looks like you need like 8 or more inches of insulation on the roof. That seems pretty extreme to me.
 

trailscape

Explorer
I don't want to derail the thread, but I'd be curious how different materials impact thermal properties and ratings when specific to camper designs. You also have the options of fiberglass, aluminum, composite, etc..

Yeah looking at those numbers it looks like you need like 8 or more inches of insulation on the roof. That seems pretty extreme to me.
 

IdaSHO

IDACAMPER
comparing recommended R-values for homes to campers is not advised.

Two completely different animals.


You are far better off to think of a camper as an ice-chest.


FYI, we have been down to -20F more than a few times with zero problems keeping 68-70 degree cabin temps.

That's two people, our custom camper that is insulted to roughly R10 in floor, walls, and ceiling, and nothing more than a 6kBTU of propane furnace.
 

IdaSHO

IDACAMPER
I don't want to derail the thread, but I'd be curious how different materials impact thermal properties and ratings when specific to camper designs. You also have the options of fiberglass, aluminum, composite, etc..

Everything impacts it.


And anything metal framed is pretty well doomed from the start from a thermal property standpoint.

The thermal bridging is terrible on units built using aluminum or steel framing is terrible.

Same goes for units that use aluminum extrusions for corners and seams, when using composites.
 

aernan

Observer
IdaShow thanks for the advice. From my initial research it looks like many expedition vehicles have some type of laminated foam insulation as the main walls and roof.

What confuses me is the Stewart & Stevenson LMTV series have a S-280 shelter on them that is constructed from what looks like square aluminum tube and foam insulation with a thick aluminum skin on the inside/outside. I am guessing there would be thermal bridging everywhere. On the flip side the structure is massively strong and is direct attached to the frame with no 3/4 point tortion frame under it.

I'm doing the initial calculations to see how much solar it would take to run an AC unit in a warm climate to see if there is enough roof space. If not it will help me size a generator. For heating I think there are lots of good options and it should be fairly easy to get the place warm enough.
 

ebbs

Observer
comparing recommended R-values for homes to campers is not advised.

Two completely different animals.


You are far better off to think of a camper as an ice-chest.


FYI, we have been down to -20F more than a few times with zero problems keeping 68-70 degree cabin temps.

That's two people, our custom camper that is insulted to roughly R10 in floor, walls, and ceiling, and nothing more than a 6kBTU of propane furnace.

That's what I've been thinking. I was looking at building my project out of rhinokore which has a 1" R value of 3.19, meaning to get to tier 5+ standards I'd need 6"+

Thinking about it, as you described like a ice chest, air space in an ice chests really effect the efficiency. knowing that, means to a point, the smaller the enclosure the less insulation needed. since most of us aren't dealing with even a small apartment sized space, it's clear to me that we could get away with less insulation. The issue is figuring out just how much less.

I've read some experiences with the rhinokore as an enclosure in Canada that said they had great experiences with cold. I can't remember the specifics on exactly how cold they experienced or how thick the walls were, but I know there was snow and think the walls were 1.5-3".

From my research, the biggest thing is getting rid of thermal bridges and using efficient heaters. it'd be nice to have a chart, like residential homes do, but I suspect that with the mobile nature makes that a bit tough in more than one way.
 

aernan

Observer
I looked into the target values and designs. I can say for certain that entry level tow behind trailers have almost no insulation and not very efficient heating or cooling. Any solid foam insulation that is thicker than 1/2 would be on par. Some foam core materials can have very high R values. Spray foams can also be excellent. The thing that will really affect your design is windows and doors. Single pane windows are completely thermally transparent.
 

downhill

Adventurer
In a camper sized space, the dominate factor in thermal efficiency is not R value of the walls. It is air exchange. Two people require approximately 1.6 CFM of fresh air exchange to maintain adequate levels of O2. In a 2000 sq ft house, that would be one exchange every 10,000 hours. In a medium size camper, it is more like one exchange every 2.5 to 3 hours. That is a pretty massive air leak. The best strategy is to eliminate cold bridging, including windows, and maybe shoot for an R value in the walls of 5 to 7. Any more than that is mostly wasted. One camper that I built was insulated with a total of 1/2" of material. It could be kept comfortable down to 10 below with just 3,000 BTU. Like all campers though, it requires a steady heat source. No matter what the R value, the heat goes out with the air exchange.
 

java

Expedition Leader
I have 1.75" in the walls, and 3.75" in the ceilings. None in the floor yet. It stays warm with a 1500W electric heater at freezing. Have a 3500W (just under 12k btu) Webasto and it cooks us out. I did not do a great job on thermal bridging, its aluminum shell, alum frame windows etc.

As to venting, I leave one or both roof vents open all the time, way too much moisture inside otherwise. Heater works a little harder, but its a good trade off IMO
 

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