Insulation
Insulation’s job is to slow heat flow by Conduction (see Building Science Basics). Air flowing through or around the insulation will greatly reduce or even nullify its’ performance. Therefore, airsealing must be done before adding insulation.
Insulation Types
Reading about insulation types is confusing, everyone has a bias (including us). Here is a frank discussion of the insulation types and their pros and cons. Which products we recommend depends on the project, the budget, and the goals to be met. We are not product people, we are solution people and will recommend whatever has the best chance to deliver results.
Cellulose
Description
80-85% recycled newspaper with fire and pest retardants added. Delivers R3.5/inch (loose fill) to R4.0/inch (dense pack).
Pros
Probably the greenest material because it is mostly recycled. It also takes very little energy to produce it. Inexpensive. Does not lose R-value as the temperature drops. Provides a decent air seal when dense packed. (Dense packing is like putting 3 pounds of stuff in a 2 pound box. Check out this great video from Building Doctors about dense packing techniques.) It is harmful to bugs and may reduce mice and other critters from coming into the attic.
Cons
When wet the boric acid fire retardant is corrosive to metal and brick. If installed incorrectly in walls it is prone to settling. Absorbs moisture.
Our Take
For simple attics and uninsulated walls in older homes, we like cellulose. In attics it must be paired with proper air sealing or it could cause auxiliary problems like mold and mildew. In walls when dense packed, it provides about the best air sealing possible without opening up walls, better than many types of retrofit foam insulation, in our experience. Be careful using it against brick or metal, as it can be corrosive.
Fiberglass
Description
Spun glass fibers made just like cotton candy only at 2000 degrees. Not as tasty, though. Delivers R2.5/inch (loose fill) to R3.2/inch (batt or blanket)
Pros
Essentially non-combustible. Non-corrosive. Fairly inexpensive. Easy to install. Sold everywhere. 30-40% recycled, the rest is sand which is a rapidly renewable resource. Decent R-value/inch. Does not absorb moisture. Will not support mold/fungus.
Cons
Itchy. Batts are easy to install poorly, even small installation errors can have a large negative impact on performance. Loses substantial R-value as temperature falls, approximately 20% at 30 degrees and 50% at -20 degrees. Slightly more expensive than cellulose.
Our Take
Cellulose performs better and costs slightly less, an extremely rare combination, so we tend to use it over fiberglass. Where knob and tube wiring is involved, or brick, or a number of other potential factors, fiberglass can be a better option. Recent research indicates it air seals fairly well when dense packed. However, Fiberglass batts are so often installed so poorly that they are simple not worth their price. Therefore, we recommend Rockwool batts instead, even though they cost more, because you can actual get what you pay for once installed.
Rock Wool or Stone Wool
Description
Manufactured very similar to fiberglass, except it is made from basalt and/or slag (the remains of the steel making process. Delivers R2.8/inch (loose fill) or R3.3/inch (batts).
Pros
Handles heat very well. Used as a firestop in commercial buildings. Good sound absorption, the best by a small margin. High recycled content. Much easier to install correctly, as compared to fiberglass, due to the higher density of the batts and ease of cutting (just use a bread knife). Also, it does not absorb water or support mold growth.
Cons
Somewhat itchy. Somewhat hard to find in stock, although you can special order from stores like Lowes or Home Depot. Rare in blowing wool form. Higher cost as compared to fiberglass.
Our Take
This is a nice product for using in high heat areas around chimneys and flues. Good sound insulation for interior walls around noise sensitive areas (e.g. between master bedroom and a teenager's room). Overall, a much better product than fiberglass, especially for the DIY person. Particularly excellent for adding to the outside of building or finishing the basement.
Manufacturers
Johns Manville - Mineral Wool page
Rockwool - RockWool products page
Open Cell Foam - Spray On
Description
Typically water based and very light density, this foam has the consistency of angel food cake. It weighs about .5 pounds per cubic foot. Air bubbles inside foam burst open, hence it is called 'open cell'. Some types of open and closed cell foam have a soy base, although this soy base is still typically accompanied by strong chemicals. Delivers R 3.5~3.7/inch.
Pros
Excellent air seal. Typically half the cost of closed cell foam, which is part of its popularity. Lower expansion pressures when curing, some types can be used in existing walls without breaking drywall.
Cons
R-value only equal to cellulose for 2-3 times the cost of cellulose. It can absorb and hold moisture. Chemicals used while installing it are pretty nasty and often state that no humans should go inside the building for 2-7 days after installation. Not particularly green.
Our Take
Too new of a product with too many potential health issues without superior product characteristics.
Closed Cell Foam - Spray On
Description
Typically oil-based, high density (1.25-2 pounds per cubic foot) hard foam. It is a fairly mature product that has been out for 30+ years. Made of 2 parts, it catalyzes when mixed and cures quickly. Air bubbles inside (cells) do not burst, hence the 'closed cell' designation. Delivers R6/inch.
Pros
Fantastic air seal, nothing else can touch it. Will stick to dirty surfaces. Low shrinkage, so it won't pull away from edges if installed correctly. High R-value/inch. Reduces moisture transfer.
Cons
Strong chemicals involved. In small quantities it isn't a big deal, but doing whole new houses all humans are recommended to stay away for several days. It is oil based, so it is not very green. More expensive than all other common insulation types. When it cures it exerts a lot of pressure and will break drywall and bend window and door frames so they won't shut. All forms are somewhat combustible. Occupants need to leave the home for 24 hours while product off gasses. By far, the most expensive insulation available.
Our Take
Reducing air leakage is the most important part of most jobs. Closed cell foam does a better job than any other insulation type. A great option for complicated attics or in the basement, it does not absorb water. Otherwise, TOO expensive to use everywhere.
Radiant Barriers/Reflective Insulation
Description
Tin foil on steroids. Originally called Multi-Layer Insulation by NASA who invented it for the Apollo missions, it is typically 2 sheets of foil with a different type of thin insulation between them, either bubble wrap or fiberglass. They reflect radiant energy. Sunlight is the best example of radiant energy, campfires are another example. Our bodies also produce a lot of radiant energy which is why emergency road kits often include a foil blanket. Beware, though, lots of snake oil surrounds this product. Do not believe the R-value unless it is less than 1. This is a radiant barrier (reflects infrared energy) and not a conduction barrier (R-values are given).
Pros
Reflects 97-98% of radiant energy. Great to use with radiant floors. High fire rating, so it can be left exposed in many areas. Relatively inexpensive. Easy to install, staples up. Inexpensive option for covering fiberglass in knee walls.
Cons
Need 1” or more of open air space on each side to reach their full R-value. Not effective in northern climates for reducing air conditioning bill. Ridiculous energy savings and R-values are often claimed.
Our Take
This is a very versatile and useful product. It restores R-value when we cover fiberglass in knee walls, it is nearly fireproof so we build boxes over recessed lights out of it, there are nearly endless uses for reflective insulation. That said, there is a lot of snake oil around these products, so take extreme claims with a grain of salt.
Manufacturers
Guardian Building Products - Solar Guard Reflective Insulation -or- (Cached copy)
Air Krete
Description
Essentially very, very light density concrete (Magnesium Oxide concrete and a water based foam, similar to shaving cream) that goes in your walls in foam form. Delivers R3.9/inch. However, it is not to be confused with Aircrete which is a structural concrete product.
Pros
Non allergenic, extremely mild chemicals, very good R-value/inch, does not shrink, does not break drywall.
Cons
About 3 times the price of cellulose or fiberglass. Finding an installer maybe hard in your local area.
Our Take
The best foam option for existing walls. Probably the best option, period, for brick walls.
Interesting Links
For more technical information, the Wikipedia article on R-value is excellent
Department of Energy - Insulation Comparison
University of Colorado – In a Cellulose vs. Fiberglass study(Cached copy) in 1989 and 1990 comparing identical fiberglass and cellulose insulated structures, the cellulose building was found to have about 35% less air leakage and use about 26% less energy to heat.
Department of Energy – Cellulose vs. Fiberglass studied effective R-values of fiberglass and cellulose as the temperature changes. This is where we get our factoid that fiberglass loses about 20% of its R-value at 30 degrees and 50% at -20.
Department of Interior -Detailed Insulation Comparison from 1995 (cached copy)
Oak Ridge National Laboratory - Radiant Barrier Fact Sheet
Take the information from the following 2 websites with a grain of salt, although they do have good installation techniques.
Fiberglass and Rock Wool Insulation Manufacturer's Association
Cellulose Insulation Manufacturer's Association