What’s the best choice for “green” insulation in the new addition to our house?
New York, New York
There are several good alternatives to fiberglass insulation if you want a “green” product to insulate the addition.
Insulation made from recycled denim is treated with a fire retardant. It’s not made of used fabric but scraps from the manufacturing process. In general, growing cotton is tough on the environment because of the heavy use of pesticides, so this may not be the best option, although it’s a good use of otherwise wasted material.
Wool insulation provides an option that is natural and renewable. Although wool is flame resistant naturally, it is subject to insect damage. So the insulation is usually treated with boron to deter insects. But boron is a naturally occurring element and not known to be carcinogenic.
Cellulose insulation is probably your best bet. It’s made from 80% recycled newspaper, and the chemicals that hold it together do not use formaldehyde. Fire-retardant chemicals are also necessary to make the product safe. R-values of fiberglass, wool cellulose are similar, but can vary significantly based on a number of factors. Cellulose insulation is more affordable than wool insulation, too.
Don’t overlook Structural Insulated Panels (SIPs) as an option for building the new addition. SIPs are basically slabs of polystyrene sandwiched between two sheets of oriented strand board (OSB). Because the polystyrene allows very little air to pass through the walls, they produce a super-insulated structure.
— Troy Griepentrog, senior associate editor