What Is the Greenest Insulation? The Case for Mineral Wool

mineral wool carry
©. Greg Lavardara

© Greg Lavardara

One of the toughest decisions in green building is the choice of insulation. Each type has its own set of virtues and problems. Last summer I wrote an article to try and address this confusion. I didn't even mention rock wool, and have pretty much always sort of lumped it together with fiberglass.

Not so; architect Greg Lavardera claims that it is very different, and if " you think that Mineral Wool batts are similar enough to Fiberglass batts that you already know what you need to know about it, then you are a fool." So, fool that I am, I continued reading.

Greg first makes the case that batt insulation has merits that we overlook.

Lets make this absolutely clear: There is Nothing wrong with insulation in the form of batts. Batts are a convenient way to package insulation for transport, handling, and installation, which is why it is the predominant form for insulation in the US....Lets summarize the lesson here. What most green pundits blame on batt insulation is the fault of fiberglass insulation. While Mineral Wool is also a batt, it is a completely different product with many different properties. It does not suffer from any of the above problems of fiberglass, yet retains the best part - its easy to handle, easy to install, and best of all your labor force already knows how to do it. That is no small point.

Greg concludes:

Mineral Wool's rigid shape and ability to be measured and cut accurately enables it to fill stud voids more completely than any other insulation product, with less effort, and more speed. Mineral Wool fits into the building practices of 99.9% of Americas' builders with no need for new process, extensive re-training, or changes to new sub-contractors, new suppliers, and new business relationships. Mineral Wool is the easiest way for the vast majority of builders to step up their game and start building better.

Then Greg shows an installation in a factory, with walls laid on their sides, with a big mitre box cutter to make the cutting of batts perfectly square. Except in the real world that isn't the case; there are wires, there are studs that are not perfectly square, they are using a knife instead of a mitre saw, and they are getting paid by the square foot like every other batt installer. Then all the virtues of the insulation disappear and it becomes as leaky and awful as fiberglass. Call me a fool, but I do not see how the stuff is intrinsically going to result in a better installation. In BuildingGreen's Guide to Insulation Products and Practices, he writes about mineral wool:

Proper installation is key: Performance is significantly compromised by poor installation—such as compressing batts behind wiring in a wall cavity. Greater rigidity of mineral wool batts makes this installation mistake less common than with fiberglass batts, but as with fiberglass, care must be taken to cut batts accurately (with a knife or saw) around electrical boxes, etc.

Greg then turns the rant away from support of mineral wool to an attack on cellulose, the darling of the green building industry. I have never been comfortable with the stuff, and neither is Greg.

Its made of shredded newsprint. Thats it. It is fire treated because as you might guess it would be dangerous otherwise. A warning - water and moisture will quickly separate the newspaper from its fire retardant. Any wall failure or introduction of water into a wall with this insulation becomes a greater concern than the threat of mold. You have to be sure the fire retardant has not been compromised. Add to this wall configurations without interior vapor retarders, and you may be playing with fire, literally.

I am not certain that this is really true. First of all, if the stuff gets wet it is probably ruined anyways, which is one of the reasons I don't like it. Alex Wilson writes that " soaked cellulose will often slump, resulting in major voids and loss of insulating performance. Should be avoided in applications where moisture is a significant concern," which for me, is every wall north of Phoenix. Secondly, it would need a lot of water to wash away the boric acid. Thirdly, all kinds of insulations are flammable, which is why we protect them with drywall. And burning newspaper is not going to be as quick a killer as burning plastic foams. But Greg really doesn't like it.

It is "designer" insulation, made from garbage, riding on the hype of its recycled content. Its the Emperors New Insulation. Buy into the hype - be my guest. Don't expect the rest of the industry to come along with you.

So while I agree with much of Greg's complaint about cellulose, I am not yet convinced that mineral wool is the definitive answer; I remain confused. But I am certain that Greg has started what will be a lively discussion. Read it all at Greg La Vardera Architect