Wednesday, December 21, 2011

Insulation Choices

Now that all my Christmas parties are done, I can re-focus on issues about making my houses more energy efficient.

I say my houses like I really own a bunch of property. I have my house built in the 1950s which is less than 2000 square feet but certainly large enough for my cats, 2 doggies, my craft supplies and me. Really my craft supplies and craft magazines take up the most space.

I bought a 1960s house to renovate that is less than a 1000 sq. feet and I rent that out to Kathy and her family. We needed enough space for Kohle, the greyhound, to be able to run.  The house did not have one speck of insulation in the walls unless you count a few widely scattered areas of crumpled up newspaper. It does have some fiberglass batts in the attic that are actually installed better and thicker than the ones in my house.

Ok, so those are my two houses. Well, I’ve been getting into some other buildings that require insulation. One of my family members lives in a mobile home that is less than adequate as a living space. So the first step in getting my brother, John, into a real home is to build a shop. He is a cabinet-maker but he needs space to be able to build cabinets for his new home (and my kitchen, bathroom, my other brother’s kitchen, Kathy’s kitchen and bathrooms, etc, etc.). We (well, really it’s Randy, Carlton, Chris, Don and Buck) are building a beautiful shop for him. We are also using it as practice for the issues you face in building a home.

We are now at the stage for insulation. I thought I would go over my decision-making process for choosing insulation.  I’ll briefly review the choices with pros and cons for the main categories of insulation – fiberglass, cellulose, denim or cotton, and mineral wool.

The shop is on relatively low-lying land in the humid South so moisture control is an issue. Since it is a woodworking shop, fire resistance is also a consideration. I am not considering foam for this particular building so I will not be discussing those choices here, though I will discuss it when we talk about building and insulating a house.

All of these forms of insulation have an R-value (resistance to heat flow) between 3-4. Since they are not very different, the R-value will not be the determining factor.


1.     Pros – commonly available, cheapest insulation, familiar installation, R value equal to most other insulations except for foam, lightweight, some brands no longer have formaldehyde binder so no off-gassing, sometimes uses recycled glass, resistance to moisture damage and fire are rated as excellent, can be blown in

2.     Cons – high embodied energy in making fiberglass (10 times as much energy to make fiberglass as it does to make cellulose insulation), little recycled content, difficult to install well, more air permeable than most other insulation, prone to convective loops since it is a low density material primarily composed of air, similar problem is “wind washing”, difficult to recycle, cannot compost, questionable health effects from inhaling glass fibers (the fiberglass industry heavily disputes these claims). Itchy unless encapsulated, requires protective clothing


1.     Pros- commonly available, pretty cheap, can install DIY attic installations, R-value similar to fiberglass (generally 3-4 per inch), low embodied energy. No other insulation uses less energy for production. Since it is primarily made out of newspaper, keeps newspaper out of landfill. Ties up some carbon from the newspaper. Borates used for fire resistance and mold prevention are safe chemicals. Can moderate moisture in air. Better air barrier than fiberglass though not rated as an air barrier, compostable.  Good retrofit for insulating intact walls

2.     Cons – holds moisture if it gets wet, fire resistance is less than fiberglass, dense pack installation in walls difficult for DIY (need commercial grade blower, not one from the large stores), wall installation may leave voids, gaps. Can support some mold growth if very wet. No batts available(why don’t we have cellulose batts?), settling can occur if not properly installed, requires dust mask

Denim or Cotton

1.     Pros – very easy, pleasant DIY installation, not itchy at all, somewhat available, R value similar to fiberglass and cellulose, not too expensive, low embodied energy as the material used is recycled, usually pre-consumer though some post-consumer fibers are being used now, no formaldehyde binders, uses borates for mold and fire resistance, sound reduction, no protective clothing required though a mask should be used for cutting the batts, better air barrier than fiberglass though not rated as air barrier

2.     Cons – can be difficult to find, only available in batt form, can’t do a retrofit unless the wall is open, poor moisture resistance, moderate fire resistance, can have gaps, must install carefully behind wires and boxes similar to fiberglass, can be hard to cut (but tears easily)

Mineral Wool – 2 main forms, rock wool from basalt (volcanic rock) and slag wool from blast furnace slag (material that forms on surface of molten metal)

1.     Pros – durable, fire resistant (withstands temps up to 2150 F), no release of toxic gases, will not absorb water, R value similar to fiberglass and cellulose, will not support growth of mold, mildew, bacterial growth, available in batts or blown in, batts are relatively easy to install, a little less itchy than fiberglass, no chemical off-gassing, no fire or mold retardants, no health effects, good sound absorption, better air barrier than fiberglass (though it is not considered an air barrier), can be reused, does not deteriorate

2.     Cons –difficult to find, no local sources, expensive, relatively high embodied energy to produce, requires careful installation like fiberglass to avoid gaps


For John’s shop, I have chosen mineral wool insulation based on its fire resistance, moisture resistance, and sound attenuation. I am not a fan of fiberglass at all and feel that any of others would be superior to fiberglass. Fiberglass just allows too much air to circulate (convection currents, windwashing) through for me to consider that as a viable choice in insulation. I did not choose denim or cellulose primarily because of the moisture issue.


“Installing Fiberglass Right” in Musings of an Energy Nerd, Green Building Advisor July 2009

“A Visual Guide to Why Fiberglass Batt Insulation Underperforms” in Alison Bailes blog, Energy Vanguard

“Should Batt Insulation be Outlawed” in the Green Building Curmudgeon blog, Green Building Advisor

“Insulation Education” by Max Alexander, This Old House Magazine,,20435285,00.html

“How to Make Your Home More Energy Efficient” TLC website

“What is Wind Washing (and why every homeowner should know)?” by Erik North July 8, 2011 on the Energy Auditing Blog

“Fiberglass-Batt Insulation” in How It Works – The Mechanics of Home Building by Rob Yagid in Fine Homebuilding August/September 2011

“Heat Transfer Through Insulation” in How It Works – The Mechanics of Home Building by Rob Yagid in Fine Homebuilding September  2009 pp. 16-17

“Insulation Comes of Age” by Alex Wilson in Fine Homebuilding, March 1, 1996,pp 46-53

“Blown Cellulose Insulations” in John Brooks Real Homes for Real People Blog.


  1. The shop is looking good! You are making nice progress!

  2. John is so happy with it. He says "You can't get better carpenters than Carlton and Chris." Which is high praise from a cabintetmaker to a carpenter.