Hard foam insulation, aluminum side facing out or in?

[ioan]

I'm installing the insulation on the roof of my teardrop, should the aluminum foil side face the outside? Is how I installed it in the side walls, but I can't find anywhere the right way to do it. Help?

[GuitarPhotog]

I installed mine with the aluminum side facing in.

Yesterday.

It seems logical to want to reflect the interior heat back in, right?

<Chas>

[ioan]

I installed mine with the aluminum side facing in.

Yesterday.

It seems logical to want to reflect the interior heat back in, right?

<Chas>

Well, I was thinking that I want to reflect the heat (and cold) out! Inside I'm pretty sure it won't be cold, 2 people sleeping in such a small place... even at home, in the winter we sleep at night with the window cracked (we like to sleep in cold air, warm under the blanket)
Hmm, any other opinions?

[ioan]

Man, I posted this in the wrong place... I'll x-post in the right one.

[ioan]

(I originally posted this in the wrong place, here is the post and answer I got)

I'm installing the insulation on the roof of my teardrop, should the aluminum foil side face the outside? Is how I installed it in the side walls, but I can't find anywhere the right way to do it. Help?

I installed mine with the aluminum side facing in.

Yesterday.

It seems logical to want to reflect the interior heat back in, right?

<Chas>

Well, I was thinking that I want to reflect the heat (and cold) out! Inside I'm pretty sure it won't be cold, 2 people sleeping in such a small place... even at home, in the winter we sleep at night with the window cracked (we like to sleep in cold air, warm under the blanket)
Hmm, any other opinions?

[Gage]

Man, I posted this in the wrong place... I'll x-post in the right one.

Must have been a long day.

[bobhenry]

Polyisocyanurate foil faced foam boards are semi porus and can encapsulate small amounts of water. It is also degraded by UV light. The foil face is applied to combat both of these problems. External seams are to be foil face taped to block water intrusion. The foil side should face the elements. In this position It will also reflect a portion of the solar gain.

Once you have blocked out these elements you CAN add a second interior layer as a vapor barrier on the interior side of the wall

[GuitarPhotog]

You don't "reflect cold"

Cold is the absence of heat. The role of insulation is to keep heat on one side and not permit it to travel to the other side.

Putting the foil side out helps reflect heat out, but will make no improvement in the heat retention inside the trailer.

Since I'm insulating a metal trailer, putting the foam side out doesn't add anything to the ability of the outside to reflect heat out, therefore I put it on the inside.

That's my story and I'm sticking to it.

<Chas>

[GuitarPhotog]

See my reply in your original thread

viewtopic.php?f=40&t=49284

[ioan]

You don't "reflect cold"

Cold is the absence of heat.

I said that as a joke ;-)

Since I'm insulating a metal trailer, putting the foam side out doesn't add anything to the ability of the outside to reflect heat out, therefore I put it on the inside.

Well, it does (I think). The aluminum exterior, when hot, is going to radiate infrared, and the aluminum foil is going to reflect away part of it. As I said before I'm not afraid that I'm going to be cold in the trailer, it's easier to put another blanket on.. but what if is way too hot and I have nothing else to take off? :-)

[aggie79]

I believe radiant barriers only work if there is an air gap, so if the foil of your insulation is tight to plywood there will be heat conduction but not radiation. It will function as a vapor barrier as Bob said (unless you have the foil that is punched with small holes to allow moisture vapor to permeate.)

[SteveW]

I believe radiant barriers only work if there is an air gap, so if the foil of your insulation is tight to plywood there will be heat conduction but not radiation.

^ This ^ If there is no air gap, the foil really serves no purpose other than as a vapor barrier.

Hmm, I might need to look into a pop-up canopy that has foil on top. Haven't seen one, but that seems to be a perfect application for it.

[deceiver]

From Maine here, where insulation is an art. When you insulate a house, we hang and staple plastic to the inside of the studs in the walls. If you put it on the outside, moiture gets trapped there and will actually flood the walls. So, any moisture proof barrier goes on the inside.

On another point. shiny aluminum reflects light that can be converted to heat, or infrared energy. But will heat be reflected by aluminum? Actually isn't aluminum a good conductor of heat?

Put sheet aluminum in the sun and it will stay cool. Put a hairdryer blowing on it and it will heat up and transfer it to the other side better than most other materials.

[Martiangod]

I put the foil inward, filled all gaps with spray foam, then foil taped every seam, corner and so on to prevent internal moister from getting to the insulation. Foil faced styrofoam degrades approximatley 20% in the first 5 years, faster with moisture intrusion.
Condensation is a trailer killer, and the build up in a small box is high, with foam it is especially important to have a vapour barier, more so then in tin and stick construction, that by its nature breathes.
Ever tryed to pick up a hot tob cover, leatherette wrapper styrofoam? Saturated
If you cool weather camp you know how much condensation builds up, its exagerated from warm weather camping but its still there.
Anything put on the cold side needs to breath, like Typar. Otherwise your roof will rot from the inside out.
Even though I put styrofoam in my roof, 2" SM, i crowned 2x4's so there is an air space on top of the insulation so the ply can breath.
I've replace to many rv roofs in 29 years of working on them

And the main reason for a surface coating on white insulation is to make it easier to work with, so it doesn't break so easy when cutting and handling. Trying to mimick the workability of XPS foam board due to loss of market share to the XPS foams.
And marketing the foil coating as providing higher R value, again due to the higher R values of XPS board.
The foil is basicaly a marketing ploy