Blown-in insulation

Brad White_200

It depends what type and how applied.

Blown-in cellulose can vary from 2.0 to 4.0 depending on density and settling. The newer "dense-pack" cellulose applications can get you to the higher numbers. A typical conservative value would be about 3.4 in my estimation for a good cellulose job under the older standards using larger nozzles.

If short-fiber fiberglass, roughly the same story but air infiltration through the material if you do not have good air barriers, will reduce this.

Rock wool or mineral wool will be in the 2.5 range as it tends to be rather clunky and lumpy with air gaps.

Icynene will get you an R of 3.4, same as fiberglass batts, but with high integrity and good air sealing ability. (Fiberglass works well in a lab, not so much when it is not properly sealed from ambient air. Fiberglass's R-value diminishes the colder it gets due to internal convection.

Urethane foams (Corbond among others) can get you to the R-6 aged or R-7+ range new and are also air tight. They are more brittle than Icynene which is almost fluffy/spongy and flexible against settling.

So, what was your question again? :)

Ryan_8

Blown-in insulation

How do you measure the "R" value for blown-in insulation?

Mike T., Swampeast MO

GREAT reply Brad. I must add that in my renovation experience, earlier cellulose insulation (not the new "dense pack") tends to settle significantly while fiberglass tends to stay pretty well where it was installed. Unfortunately though, blown in fiberglass seems to be awful with regards to infiltration--if the wind can blow through the outer wall skin it will blow right through the fiberglass as well...

I've also found that there's no such thing as a "waterproof" house. They may start almost perfectly so, but over time and under "unusual" weather conditions they all seem to leak. Blown in cellulose will absorb water just like a sponge and since air does not move through it easily, it can set up some ideal conditions for rot. Fiberglass on the other hand does not [appear] to be affected by small amounts of water and since air can move through it rather freely, it tends to dry relatively quickly before nasty problems set in.

I've been watching a number of high end (for my area at least) homes built in the last 18 years or so and most of the style I call "multi-gable monstrosity". They are NOT faring well and I suspect they'll rot into the ground well before my old frame house built in 1903. I can only hope that my small, recent addition using modern framing (but old solid sheathing with plain old tar paper on the outside) will fare well and that my meticulously installed batt fiberglass wall insulation won't cause a problem despite some water intrusion that is historic, ongoing and seemingly unstoppable in "unusual" conditions.