Foil in or out?

sediener · 06-07-2008, 04:28 PM

I'm insulating my garage door (in anticipation of a garage A/C

) and picked up 4 sheets of 1/2" foil backed R2.9 styrofoam and 4 sheets blue 3/4" R4 foam board to cut and stick in the panels. I might be able to cram another 1/2" foil in there and have foil on both sides but we'll see how tight it is once I get what I have in there. Then again there is always great stuff to tighten things up.

So, should I put the foil facing the outside or the inside? I'm thinking outside since I want the heat bounced out as much as possible.
- Steve (hiding inside until it drops below 90)

LeftyTom · 06-07-2008, 05:26 PM

I think the foil goes toward the door, to act as vapor barrier.

Gotcha6 · 06-07-2008, 05:28 PM

This is a product typically applied to the outside of studs as sheathing, and the foil should go outward, acting also as a vapor barrier. But as you are using it on a garage where moisture control cannot be readily achieved, and assuming it's a metal garage door, it doesn't really matter for that aspect. I'd probably put it up as the innermost layer and with the foil in if you aren't covering it with anything else to help prevent UV breakdown on the insulation. Even blue styrofoam will deteriorate with time when exposed to light.

sediener · 06-07-2008, 05:45 PM

thanks,

It's a metal door and I'm just filling the voids in it with foam to help keep it reasonable in there during the summer. (All the foam would be on the inside of the door so not so much of a worry for UV breakdown) I was thinking the foil would go closest to the metal since I saw this: http://texasgarages.com/insulation.htm and the foil reflective property is pretty much the only "insulation" that provides.

- Steve

Gotcha6 · 06-07-2008, 06:52 PM

All insulations act in one of two ways; reducing convection/conduction by trapping air, or reducing radiation by reflcectivity. This system looks like it will work by trapping the air in a void between the film and the metal door panel. I suppose they require the panel to be calulked up and a vent hole left somewhere. It's like making an insulated glass panel. The foil is also a very effective radiation barrier. The vinyl covered option appears to be for esthetics.
Your styrofoam will do just as well if it is placed to avoid drafting through the barrier & the foil will help no matter where you put it. Good luck.

Glennbear · 06-07-2008, 08:56 PM

Originally Posted by sediener

I'm insulating my garage door (in anticipation of a garage A/C ) and picked up 4 sheets of 1/2" foil backed R2.9 styrofoam and 4 sheets blue 3/4" R4 foam board to cut and stick in the panels. I might be able to cram another 1/2" foil in there and have foil on both sides but we'll see how tight it is once I get what I have in there. Then again there is always great stuff to tighten things up.

So, should I put the foil facing the outside or the inside? I'm thinking outside since I want the heat bounced out as much as possible.
- Steve (hiding inside until it drops below 90)

I insulated my 16 foot wide door using a sandwich of foil faced and plain foamboard with the shiny foil facing the door. Despite the recent heat wave and the east facing door, with good wall and ceiling insulation a small window AC unit has kept the 24 x 24 shop at 75 degrees or less. Here is my original thread with pics:

http://www.ncwoodworker.net/forums/f...ge-door-12486/

Note : The foil faced board I used had two foil faces, I used the more shiny side against the door skin.

sediener · 06-08-2008, 04:07 PM

That looks familiar, except I have a nice blue color. I spent all morning installing the insulation and it is still hot as heck in the garage... I guess I'll need that AC unit too, huh?

- Steve

cpowell · 06-08-2008, 07:41 PM

You're gonna be spoiled once you get the AC installed and cooling. I have a marginally sized unit for my 20 x 24 shop...it keeps things pretty cool unless the DC is running non-stop.

The shop is insulated very well but there is a fair amount of mass in the shop that needs to be cooled/heated. I noticed when I use the shop frequently it is easier to keep cool. If I don't go to the shop for a few weeks then the temp is probably pretty close to avg or median outside temp.

Chuck

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