Rigid Foam Insulation?

[rumblecloud]

Hey...I'm putting foil-backed rigid foam on the interior walls of my workshop in the pole barn -1-1/2 inch thick. I'm supposed to put the foil side in to reflect heat back into the space. But what does that matter if the insulation is going to be covered anyway?
I'm still going to do that, but just curious because when it's used outside, the foil faces out and is covered -- so how does that reflect heat back into the living/work space

Do we need a forum category for construction questions - not that we have a ton of them

 

[Jazzer]

The foil face goes towards the inside, but there has to be an airspace on that side for thermal radiation to reflect back into the building.

If your interior covering is tight against the foil, little to no reflection occurs. You could do batten strips on top of the foil before your interior panels, but that's kind of a hassle.

-Jazzer

 

[rumblecloud]

Dang...that's really good to know. I was going to use the 1-1/2 inch which would have left 0 space. So I'll drop down to1 inch to get close to the 1/2 inch space (pole barn construction 2x4s are on their side). And dropping down to 1 inch saves me a couple of bucks per sheet.

 

[Uncle Gump]

I wonder if the half inch thicker insulation is a better bet then the reflective surface?

 

[rumblecloud]

Don't really know and probably no way to find out. The 1 inch is rated R-3.85 and 1=1/2 inch is 5.78.
There's a $30 difference between the two for the amount of sheets I need (14), so not a big deal. I'm headed to the store this morning so I'll figure it out on the way.

 

[alwaysFlOoReD]

Iirc, 5/8" or less air gap in windows prevents circulation, and non circulating air has an insulation value. I dont know what that is tho. So making sure that air can't circulate will be very important to insulation values. A vapor barrier and proper caulking on the inside would be money well spent IMO.

 

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I've installed radiant barriers for a few people. They seem to really like the results. Different product, I know, but may be an alternative to the air gap issue.

 

[stmitch]

Pack in as much insulation as you can. Air has an R value of 0, and a gap won't do anything to stop air movement. Foam gives you more R value, and stops air movement too, which reduces drafts and effectively amplifies the R value.

 

[alwaysFlOoReD]

Pack in as much insulation as you can. Air has an R value of 0, and a gap won't do anything to stop air movement. Foam gives you more R value, and stops air movement too, which reduces drafts and effectively amplifies the R value.

If I understand window R values, air has an R value. Iirc the gap between panes cannot exceed 5/8" or the air will circulate and transfer heat from one glass pane to the other. Less gap and the air is stationary and no heat transfer. Granted, I'm no scientist , but I've installed thousands of windows and looked into the insulation properties of them. So I'm assuming the same properties would apply to an air gap with other types of material, but I dont really know. But I do know that stopping air movement is critical to making the most of whatever type of insulation you have. Pressure difference between inside and outside will cause air movement thru the walls unless dealt with. I've pulled enough dirty fiberglass to see that first hand.

 

[Vindictus]

In every house I've done with ridged insulation. 2 inch ridged 1 inch air space , stud up 2x4 wall insulate with bat insulation give you R-25. And if you want to know why the air space leave the bat's out of one space for one day and then hold your hand in the gap and you will feel the cold air. The air gap lets the cold air coming in get warmed by the hot air going out so you don't have cold up against hot. It matters enough up here for it to be put in the building code for insulating basements

 

[sgtsandman]

I think the air gap is also there to prevent moisture build up and mold issues. But I may have the wrong application in mind.

 

[Roert42]

Air is an ok insulator. Two slabs of steel with an air gap is better then two slabs of steel butt to butt. Much less temperature transfer.

I think even on the pink batten insulation it tells you not to pack too tight or it musses up the transfer.

 

[sgtsandman]

He said butt...

 

[Uncle Gump]

He actually said Butt to Butt...

Someone needs to tell him he's doing it all wrong.

 

[rumblecloud]

Not that there's anything wrong with that...