How much insulation???

[Scott L]

My current trailer has 3/4" plywood walls and an insulated ceiling. On a ski trip last year, on a night when the temperature dropped to -8 F, I decided that my next trailer would have insulated sandwich walls in addition to the insulated ceiling. I'm just wondering if I should go for 1.5" in the walls or is 3/4" insulation enough? From what I've read, most of you are going with the 3/4" insulation.

Thanks,
Scott

[mikeschn]

Scott,

Plywood thickness
(inch) R-value
1/4 0.31
3/8 0.47
15/32 0.59
1/2 0.62
19/32 0.74
5/8 0.78
23/32 0.90
3/4 0.94
7/8 1.09
1 1.25
1-1/8 1.41

I'm looking for something similar for extruded polystyrene, but I happen to know that 1/2" EPS has an R-value of 3.0 and I believe 1" EPS has an R-value of 5.0. So 3/4" would be 4.0, right?

So compared to your wooden walls, by building up a sandwich of wood, 3/4" EPS and wood, You'll probably have an R-Value of 4.62.

Unless you are planning on camping at the south pole, (or maybe Colorado), the 3/4" EPS is probably plenty.

However, RPH used 1 1/2" insulation...
http://tnttt.com/viewtopic.php?t=12820

Mike...

P.S. Remember too, that you want to keep a window cracked to get some fresh air in there. That kinda wipes out some of the benefit of heavy insulation.

[dwgriff1]

Scott,

I used 1" of white on the floor and walls and 1 1/2" of pink on the ceiling. I've slept in it to plus 10, and after it warmed up a bit was comfortable.

Doing it again, I'd do it pretty well the same, though I'd probably use at least Pink.

Remember that 1/2" foam is rarely 1/2" and so on. Frame afer you buy the insulation.

Pink or blue is the easiest to find, but there is a black that is better yet.

Keep your framing lumber quite thin. You don't need real thick framing, it is the resulting sandwich that has the strength.

dave

[Arne]

My current tear has 1/4 ply in/out, with 3/4 insulation. It warms up easily, but the walls are cold when it is 30 outside. My next one is going to have 1/8 in and out and 1.5 insul. And, I may carpet the part I touch at night while lying down... cold walls just don't feel good.

Framing is not a problem, except the perimeter. I had wanted to cut it out of 2 thicknesses of 3/4" ply, but 3/4 ply is not 3/4, it is slightly less, but 1.5 insul is usually 1.5, so the perimeter would have to be built up with a piece of 1/8, but I want the insul to completely fill the void for stability, because of the 1/8" walls (I want to glue the walls to the insul as well)... I have not figured out exactly how to solve this problem yet.

[dwgriff1]

Arne,

That is the problem with all of these materials. None are the advertized thickness.

I framed out of double layer of 1/2 Obece ply, but it wasn't enogh and I had to put in a spacer. If I build again, I'd bend the out frame over a form (Mike did it that way on his UltraLight start) and stick frame the walls.

There is a point where this is redundant, however. My windows are single strength acrylic. That has pretty low insulation value. To make a real difference that needs to be dealt with.

And then there is the ventilation issue. My guess is that we could crack our windows less and get away fine.

dave

[mikeschn]

I may have a few inches of space between the bed and the wall on the next build. So I won't have to touch the walls at all.

And I am considering bringing in the fresh air closer to our feet instead of thru the door windows. Using the windows, my back always gets cold from the night air.

Mike...

And, I may carpet the part I touch at night while lying down... cold walls just don't feel good.

[Arne]

Dave, that is probably the best way.. I don't like building forms, but what you say makes sense.... I could build it to the thickness of the insulation, and it would actually be a lot cheaper than buying 4+ pieces of 3/4 ply. That's exactly what I did to add the galley to my tear.. I expoxied 4 pieces of 1/4 to build up a frame to attach the new 1/2" ply to......

[Scott L]

Because of the differences in the thickness of framing materials and insulation, I've wondered about the practicality of building hollow walls and filling them with expaning foam. I'd have to drill holes in the exterior walls to spray foam through and to allow for the escape of too much foam but I'm going to cover it with an aluminum skin anyway. Is this a viable solution? How do I make sure that I don't end up with any large air pockets?

Thanks,
Scott

[Kevin A]

Because of the differences in the thickness of framing materials and insulation, I've wondered about the practicality of building hollow walls and filling them with expaning foam. I'd have to drill holes in the exterior walls to spray foam through and to allow for the escape of too much foam but I'm going to cover it with an aluminum skin anyway. Is this a viable solution? How do I make sure that I don't end up with any large air pockets?

Thanks,
Scott

If I recall, someone tried this with limited success, it made quite a mess with foam oozing all over and had a tendency to distort the sidewalls as the foam expanded.

[apratt]

How about buying rough cut 1x then plane it down to the thickness that matches the insulation.

[dwgriff1]

Arthur
Yea, that is what you do. Buy thick and plane it down, or glue up sections and plane them.

Scott,
I wondered about framing it up, with the inside skin and having a spray insulation company spray the whole thing. It would require some sanding when it was set, but the foam would glue it all together.

Once built a VW pickup and filled most of the back seat area with foam like that. Sure made the little beastie quieter.

Arne
Often it is glue up and plane down. There are guys building without a planer, but I don't envy them.

dave

[Arne]

The ideal way would be to frame the ceiling and put in the interior ply in, then spray the ceiling from the outside.. after it set, use a 'hot wire' setup to slice off the extra. then cover the outside.

http://www.vatsaas.org/rtv/construction/hotwirecutter.aspx

[dwgriff1]

Would it be worth the trouble?

Would the advantages outweigh the pain to do it?

I decided not, for this build at least. Someone will do it, one day and they can report!

dave

[Arne]

I'm using 1/8 ply on the outside. I do not plan on doing foam, but would it I could at at reasonable price... my plan is to use flexible pink foam.. The reason foam would be nice is it would give support to the back of the 1/8 ply.... So, yes, in a perfect world, that is what I would do.