Why I Don’t Use Cellulose or Blue-Jean Insulation
Yesterday, a young builder came up to me after I spoke at the Atlantic Green conference in Charleston, S.C., and started talking about the new green house he was building. It had no-VOC paint, bamboo flooring, and insulation made from shredded blue jeans. And without thinking, I said, “So what’s so green about blue jean insulation?” The poor kid was expecting a pat on the back and what he got was a kick in his assumptions.
The whole idea about using a third-party green building verification system is to force designers and builders to look at the big picture, and to separate the “green-ness” of a product from its cost and marketing hype. The popular press is all in a tizzy about recycled-content building products. That includes anything bamboo, and über-groovy countertops, but the bulk of the things that make up a well-integrated green home are conventional products used with an unconventional attention to detail. It’s not about the silver bullets, it’s about getting the details right.
So what’s wrong with blue-jean insulation? Well, I have to drive past cotton fields here in North Carolina and they give me a strong incentive to choose organic cotton whenever I buy clothes. Even the work pants I wear are organic. Producing cotton is brutal on the land, far worse than wood fiber in every way, and processed cotton is a high-value commodity. Denim scraps diverted from the landfill? I think it’s more likely that they are diverted from a commodity stream that was already using them for another purpose, which still needs to be filled.
It would be fine if denim insulation was actually more economical and a better insulator than the alternative. But it doesn’t cut easily, so it’s more difficult to install correctly, and it doesn’t expand well to fill the cavities. It needs to be treated with fire retardants and insecticides and it can hold moisture. No wonder you won’t get a lot of green points for using it in your homes. It’s just not that green.
Cellulose retains moisture
What about cellulose? It’s just recycled newspaper, and that’s got to be green, right? Well that’s what I used to think, too, and you will get more green points for cellulose than for cotton. But I have seen what happens when cellulose gets wet inside a wall.
On two occasions, homes I have built with cellulose insulation had plumbing leaks. The moisture was absorbed and spread by the cellulose and it took days for the homeowner to notice. By the time we located and repaired the leaks, the cellulose had wicked up the water and become saturated. While the cellulose itself hadn’t mildewed, the studs, exterior sheathing and drywall were covered with mold. We removed the sheetrock and cleaned the wood and set the cellulose aside to dry. It was remarkable how long it stayed wet.
I have had trees fall on my roofs many times during ice storms or hurricanes. Fiberglass and spray polyurethane foam don’t retain moisture, it just flows right through and lets us know we have a problem. We fix the leak and move on. In homes with cellulose insulation I’m concerned about closing up a bunch of wet newspaper in my attic after a leak during an ice storm. I’m much more concerned with cellulose in walls than attics because most attics are both hot and well ventilated and foster better drying, but a winter ice storm could really lead to some problems.
Green building is about durability and performance more than it is about recycled content.
More on insulation:
Does Fiberglass Still Make Sense? – Still a popular and affordable insulation option, fiberglass batts now share the stage with a variety of other products, including blown-in products and spray polyurethane foam. Here’s a look at some of the offerings.
Installing Rockwool for Continuous Exterior Insulation – Here’s a look at how the 2018 FHB House is wrapped in an exterior layer of mineral wool insulation to minimize thermal bridging through the building’s frame.
Choosing the Right Thickness of Exterior Foam – Rigid foam applied on top of the roof improves thermal performance dramatically. But to prevent condensation on the roof sheathing, the insulation must be thick enough.
Reconsidering R-Value Recommendations – Many energy-conscious builders rely on Building Science Corporation recommendations for insulation thickness. But falling prices for photovoltaic panels prompts another look.
I still use fiberglass in my walls and I spray 8” of foam in my roofs. But you won’t see me using cellulose or blue-jean insulation in my homes.
Blue-jean insulation doesn’t cut easily, it's difficult to install, and it doesn’t expand well. It's just not that green.Photo: Courtesy of Amy Gahran.