wall insulating

[Henry Benner]

I initially built a tiny trailer with solid plywood walls but found that they 'sweat' in cold weather and on cool nights. My bedding was soaked by morning.

The present trailer uses 3/4" thick walls with 1/4" outer skins, fiberglass insulation (gleaned from an old truck camper), and 3/16" templast interior skins (looks like plastic cardboard, used for signs). No more 'sweating' and I've camped in temperatures as low as 12 deg F with an alcohol tin can heater.

There is probably a 'point of no return' with insulating your trailer. Are your windows single or double glazed? Is the floor insulated? How good is the weather stripping?

As well, consider what will happen to the rest of your gear, your food, water, when camping in cold weather. It's not much fun if you have to bring your food and water into your sleeping space every night to keep it from freezing.

[TwilightLane]

Condensation on the walls, ceiling and floor will be less when it is cool outside if you insulate. nothing worse than laying in bed and having sweaty walls...

hot & humid nights can be a problem too. in _my_ opinion, nothing worse than laying in bed and having sweaty balls...


(sorry, couldn't resist. i've camped too much in hot weather.)

[LDK]

Condensation on the walls, ceiling and floor will be less when it is cool outside if you insulate. nothing worse than laying in bed and having sweaty walls...

hot & humid nights can be a problem too. in _my_ opinion, nothing worse than laying in bed and having sweaty balls...


(sorry, couldn't resist. i've camped too much in hot weather.)

I'm building a solid wall TD

At least my ceiling and floor will be insulated so maybe mine won't get so sweaty.

[Wolffarmer]

Unless you really want to build one fast and sure you can live without insulation. Insulated it. I built mine with 3/8 outside ply and 1/4 inside ply with 1 inch of blue foam. Way over built. need not go over 1/4 outside and 1/8 inch inside. Of course you will now be building 2 teardrops at once. And once insulated you can camp in cold weather not worry about sweaty anything. I built the wall on a bench I made from a sheet of 1/2 mdf. and the inside wall is set in the thickness of the spars + the thickness of the ceiling material. After I set the walls up. then put on the ceiling ply on the nice 1 1/4 inch shelf and then the spars on top of that. Then the outer skin of 1/8 baltic birch ( after filling the space with Blue foam. The 1/8 ply on the ceiling and front of the trailer is still plenty thick enough and I would consider building the walls 1/8 inside and out.

Randy

[bobhenry]

Len , I found the answer to your question about carpet R value here

http://www.allwallsystem.com/design/RValueTable.html

We were discussing this over on Tearjerkers forum here is my spin on R value of 2 different wall styles.............

Panel #1 is a stick built panel w/3/4" Styrofoam insulation consisting of;

2 sheets of 1/4" plywood .31 ea .62 R
32sq foot of 3/4 Styrofoam 20.4 sq ft 3.75 x .64 = 2.4
7. 8' 1X3's 11.6 sq ft .93 x .36 = .3348
so your composit 1x3 and foam wall is 2.735
Wall #1 total "r" value is 3.355
A bottle of glue n/a ?
a hand full of nails and a quart of paint (inside finish)

You can add 1.056 to this wall by substituting 3/4 foil faced polyisocyanurate ( 5.4 "R" value) in lieu of the blue (or pink) foam

Panel #2 is a solid sheet of 1/2" plywood with a foam backed rug glued to one side consisting of;

1 sheet of 1/2" plywood .63
32 sq foot of foam backed rug 1.23 (see note)
wall #2 total "r" value is 1.86
1 quart of rug glue n/a

NOTE:

Curiously a material backed carpet is 2.08 instead of the rubber backed 1.23 indicating that the foam rubber is a better thermal conductor of heat and cold.

All info above subject to change by a resident thermal engineer ! Just my good guess based on my cheat sheet info.
_________________

[bobhenry]

I took this info and evaluated my builds.

My barn build was built with extreme cold weather and extreme hot weather camping in mind after freezing and baking in the lexan roof teardrop.

My barn trailer walls layer by layer out to in !

3/8" T-111 .47

3 layers of foam 90% of wall area 11.25 x .9 = 10.13

2x4 framing ripped to 2.5 " as studs 10 % of wall area 3.12 x .1 = .31

1/4 luan interior paneling .32

Total wall and roof "R" value 11.23

Had to figure the floor it was bugging me..

Trailer came with a 2x8 wood floor which I sealed top and bottom caulked and left to build on .

sub floor existing 1.875
2 layers of 3/4 foam 7.5
layer of osb as sub floor .63
material backed carpet 2.08

Total "R" value for floor 12.09

[jimqpublic]

The trick in heat flow calculations is you can't pro-rate R-value. Take the example of a wall that's 90% R-30 insulated and 10% single pane glass, which is only R 0.14. The pro-rated average would be R 27.015, but would be completely incorrect.

The U-factor is a measure of heat flow and is basically 1/R. 90% of the wall at R-30 passes only 1/30 BTU/Degree_F/Square Foot. 10% of the wall at R-0.14 passes 1/0.14 or 7 BTU/Degree_F/Square Foot. So the composite average is (90% x 1/30) + (10% x 1/0.15) = 0.74. Convert this back to R-value and you find the whole wall system gets R=1.34. Almost all the heat gain/loss is through the glass- it wouldn't matter much whether the wall insulation were R5 or R500.

...
We were discussing this over on Tearjerkers forum here is my spin on R value of 2 different wall styles.............

Panel #1 is a stick built panel w/3/4" Styrofoam insulation consisting of;

2 sheets of 1/4" plywood .31 ea .62 R
32sq foot of 3/4 Styrofoam 20.4 sq ft 3.75 x .64 = 2.4
7. 8' 1X3's 11.6 sq ft .93 x .36 = .3348
so your composit 1x3 and foam wall is 2.735
Wall #1 total "r" value is 3.355 ...

But again, you can't average R-values. The stick built panel is 1/4" plywood on each side with flat 1x3's covering 11.6 square feet or 36% of the area, and 3/4" foam covering 20.4 square feet or 64% of the area.

Ply+foam+ply gets R0.31 + R3.75 + R0.31 = R4.37; U-factor is 1/4.37
Ply+"1x"+ply gets R0.31 + R0.93 + R0.31 = R1.55; U-factor is 1/1.55

Combined U-factor is: (64% x 1/4.37) + (36% x 1/1.155) = 0.46;
Combined or "total" R-value is R-2.2

Panel #2 is a solid sheet of 1/2" plywood with a foam backed rug glued to one side consisting of;

1 sheet of 1/2" plywood .63
32 sq foot of foam backed rug 1.23 (see note)
wall #2 total "r" value is 1.86 ...

Since the rug is continuous, the added R-value is correct for this wall. Go with a bit thicker foam backing and the wall exceeds the stick-panel. Or conversely, with a stick panel work to minimize the percentage that's solid wood. If you do 4/4" x 3/4" strips instead of 1x3 you would reduce the solid wood from 36% to 14%, and the combined R-value would go up from R-2.2 to R-3.1, and you would save some weight as well.

Doing a bit of googling for "carpet pad R-value" I found that thin foam rubber pads get low values that you quoted, thick fiber mats get higher, but thick (1/2") urethane or eva foam pads are over R-2 (for the pad alone). So the basic 1/2" plywood wall with a good, soft foam pad is quite well insulated, easy to build, and cozy.

One caveat is that if you have porous insulation on the inside (carpet, open cell foam, or fiber pads), on a cold night moisture vapor will migrate through and condense against the inside of your plywood. Maybe not a big deal if you can thoroughally dry out the trailer during the day, but something to consider.

All info above subject to change by a resident thermal engineer ! Just my good guess based on my cheat sheet info.
_________________

I'm not a thermal engineer, but I do have to work with numbers all day and they aren't always what they seem. I studied up on heat calc's when I was trying to convince my dad to not go "stick built" with the two homes he's building right now. I failed though- he did 2x6 on 16".

[bobhenry]

"All info above subject to change by a resident thermal engineer ! Just my good guess based on my cheat sheet info. " _________________


SEE I TOLD YA

But thanks , I gotta re read this 3 - 4 times and try
and better understand what is happening

[jimqpublic]

...But thanks , I gotta re read this 3 - 4 times and try
and better understand what is happening

Better read it again as I just edited it.

And I make no great claims about the accuracy of my math- at work I have a two stage review process to catch blunders...

So I'll do another edit here just for fun.

We're talking about the sidewalls of the sleeping compartment. My focus is mostly on cold weather- heat gain from the sun beating down is a completely different calculation that's well beyond me.

So for the sidewalls of the cabin on a typical trailer, let's say the area is 44"x80" with some deduction for cabinets and curvature, or about 25 square feet each of 50 for both sides. Let's say you want it 60 degrees inside while it's 30 degrees outside.

R-value is 2; U-factor is 0.5

50 square feet x 30 degree temp differential x 0.5 U-factor = 750 BTU/hr

You'll need ventilation and that will probably lose more heat than you save by going to more insulation....

Back to the initial point made a few pages ago that comfort and not touching a cold wall wet with condensation is more important than superinsulation

[jimqpublic]

Finally, here's my idea (having never built a trailer, but I have owned a couple that were both much bigger and built much lighter than the typical TD.)




What do you think? The roof profile would be all curve- though rather mild curve for much of the central portion. I figure if commercial trailers can do 16" ceiling joists with long spans, a teardrop ought to be fine with the same- especially if I added a lengthwise "center rib" of plywood to help keep the curve smooth.

[len19070]

My thoughts on comparing the 2 wall systems was that both the weight and insulating values were comparable.

And that for the first time builder a solid wall would be easier to build. Even if they went to a 3/4" plywood wall.

Another factor in figuring the insulating value on the stick built wall given in the example is that almost 10sq Ft. of the 32 sq. Ft. is wood (1X3s) and not foam insulation, with gaps in the insulation its almost like wearing a good coat with holes in it.

And that's a lot of work to do, thinking somethings superior...and it may or not be.

Where as the solid wall with a continuous piece of rug has no gaps and has a consistent insulation, be it better or not.

And that brings us back to the Root question "in what Temperatures do you camp?" And for the 1 or 2 (and maybe more) times you do go into extremes what is the best solution.

Is it worth preparing for these random situations

That said, windows and doors are consistent insulation gaps in both systems.

Once again I'm not saying one is better, or that anyone has or has not had good or bad results with either...just that the 2 systems are close.

It is a personal choice.

Happy Trails

Len

[kennyrayandersen]

The real advantage to the sandwich build happens when you bond it all together. Then, you could easily use 1/8 skins on the inside and outside and they are MUCH stiffer and stronger than a 5/8 inch thick side wall (3/4 is structurally unnecessary for most teardrop trailers). Additionally, some people might be sensitive to the out-gassing of the synthetic [rubber backed] carpet. In the end either will ‘work’ but I’m betting on the more insulated version will be a bit more comfortable.

The point about fresh air is not trivial, since you are in a pretty small environment air exchanges are obviously needed, but they are needed whether you have well insulated walls or not. If you wall isn’t well insulated, and you need to leave some vent open, you are losing heat from both sources. By using a well-insulated wall, you cut the heat loss to primarily the vent source (other infiltration aside).