The foil-bubble-foil insulation thread

[TimNY]

So... a single layer of foil-bubble-foil insulation is routinely approved elsewhere for duct insulation. It's stamped R-4.2, which doesn't meet the R-8 required outside the thermal envelope.. but I digress...

I failed an inspection for having this stuff as the only insulation on the ducts. Left note R-8 required.

Contractor installed another layer of bubble wrap. Ugh. I tell contractor you can't do that and that I want test results from a 3rd party substantiating the R-4.2 claim. He sends me specification sheets. Ugh.

Got a call from the manufacturer who basically sided with me, stated the insulation was installed wrong and instructions not followed.

Anyway, here are the details I used to cite the violation:

1. Energy conservation code defines thermal resistance (R-Value) as the reciprocal. of thermal conductance. Thermal conductance is measured from one bounding surface to another bounding surface. Air spaces are not included. These bubble wraps all include an air space to achieve their rating. I spoke with the rep about this and he rattled off some other ASTM test that was needed to get those values.

2. Manufacturer's instructions state "Not recommended as the only insulation" a condensation will form.

3. Here is the good one. Manufacturer states you cannot double the material to achieve twice the R-value. If further states when this is does that the value is reduced to R-1.1 per layer. So now we know it has an actual R-Value (in the real world) of R-1.1.

Hope this helps. We all knew it wasn't right, but I needed to cite something.

 

[jim baird]

Good for you Tim.

I wonder just what the stuff was meant for if they bothered to calculate R-vals at all.

I'm told double wrapping any wrap defeats the purpose by increasing the surface area, ergo more surface heat loss. Make sense?

 

[TimNY]

It has it's use. My intent was not to discourage it's use, but to make sure it's used properly.

Strangely enough I just saw this stuff in the walls of a modular home. Looked like R-11 fiberglass batts towards the exterior (maybe R-13), then this stuff towards the interior. Modulars are approved by the State at the factory, so I'm not sure what the deal was.

 

[Paul Sweet]

The only way to get R-4.2 from insulation like this is when it has a confined air space on both sides, as in the middle of a stud cavity. In order to double the R-value you would have to have 2 layers of this insulation with air on both sides of each, plus a membrane between them to separate the center air cavities.

This is the problem with reflective insulation. In theory it works great, but in the real world of uneven stud spacing and wires, pipes, etc. in the stud cavities, it just gets crumpled during installation and the multiple air spaces are lost.

 

[TimNY]

O be honest, I used it in my own home. However, I used it properly.

Staple up radiant heat between TJIs, radiant insul stapled to the bottom of the TJI top chord, then R-19 batts resting on top of the TJI bottom chord. Works great.

 

[TimNY]

EDIT:

Finally got a reply from the State. As suspected, f-b-f requires an "air film" to achieve its rating, and air films are not permitted per N1102.1.1 (2003).

Another valid point they made is that even if the air film were permitted, there would be no air space at the corners when the duct is wrapped.

To my fellow NYS inspectors.. stop allowing the installation of this stuff!