Low: Batts, Rolls & Blankets
Fibrous materials such as cotton, rockwool and fiberglass are flexible and can be installed wall cavities and in between floor joists. They are typically available in 16 or 24-inch wide widths to fit between standard stud spacing and are generally easy to install. Rolls can be bought and cut to length and even trimmed to fit odd sized cavities. The batts can also come with a foil face to increase the material's heat reflectivity.
R-Value Per Inch: 2.9 - 3.7
Pros: This is one of the least expensive and easiest insulation types to buy and install.
Cons: Unfortunately, batts can sag over time and don't easily conform to nooks and crannies or any obstructions and must be installed in an unfinished space. Squeezing a batt to size doesn't improve its performance in any way and can only provide the R-Value of the thickness, or depth of the cavity.
Similar to batt insulation, loose-fill insulation is also comprised of fibrous and flexible materials such as cellulose, fiberglass and rockwool.
R-Value Per Inch: 2.9 - 4.2
Pros: Even though loose-fill has generally the same r-value as batt insulation, it is able to fill nooks and crannies, go over attic joists and into hard to reach spaces, therefore reducing air leakage and missing spots of insulation. When installed well, loose-fill is less likely to settle overtime. Loose-fill insulation is a great solution for unfinished attics and can be retrofitted in finished walls and ceilings.
Cons: Must be installed with blowing equipment and is generally more expensive than batt insulation.
Medium: Rigid Boards
Rigid boards are made of fibrous or plastic materials and come typically as expanded polystyrene, extruded polystyrene, polyisocyanurate and polyurethane in thicknesses from 1/2 to 2-inches thick. Rigid boards are mostly installed on basement and foundation walls, underneath basement slabs, and at exterior walls and roofing.
R-Value Per Inch: 3.9 - 6.8
Pros: Rigid boards have a high value per inch and can be appropriate for wet areas. Rigid boards can sometimes provide structural value and can replace plywood sheathing or concrete formwork, such as the case with ICF insulation. When installed on the outside of framing, rigid boards help prevent thermal bridging, which is a weak link in insulation installation. Additionally, boards can be made with a reflective side to further enhance heat radiation.
Cons: Are not available in large thicknesses, most are made with petroleum-based materials and some contain HCFCs.
High: Spray Foam
Spray foam usually comes as a one or two-part mixture, and is typically available in a can or tank. Spray foam can be applied to any surface, bonding to it to create one of the best air seals of all the insulation options.
R-Value Per Inch: 3.5 - 6.8
Pros: When using a low expanding spray foam, the insulation can be retrofitted into existing buildings, making it a great option for rehabs and renovations without damaging existing plaster and millwork. Closed-cell insulation provides not only helps prevent heat transfer and a vapor barrier, but when applied to a minimum of 2-inches, it provides a true air seal, giving it and advantage over the other insulations.
Cons: Insulation is installed wet and must be completely dry before finishing wall or ceiling. Spray foam is primarily made frin petroleum, which is a non-renewable source, however some companies are making an open-cell option with a percentage of soy. Spray foam is typically much more expensive than batt and loose-fill insulation and is generally best when applied by a professional.
When deciding between insulation options, remember you aren't limited to using just one type. For example, a good way to get the best bang for your buck would be to use hybrid: 2-inches of closed cell polyurethane spray foam for insulation and it's air sealing quality, and then fill the rest of the cavity with a rockwool loose-fill or batt insulation to the desired r-value.
Additionally, don't forget that each type of insulation has its own environmental impact. While it used to be one of the only readily available options, fiberglass insulation is generally shunned these days because of its association with formaldehyde, irritating chemical additives, energy intensive manufacturing process and permeability to air leakage. Cellulose and rockwool are good alternatives because of their high percentage of recycled content; additionally, rockwool is naturally heat-and-mold resistant so it does not need any special chemical treatments. Lastly, while polyurethane foam uses a non-renewable resource (petroleum), it is able to make up for it by its very good insulating and air-sealing properties, therefore reducing a building's energy use and providing a good lifetime performance.
(Image via Green Home Guide. Originally published 2010-04-14)