Used to be that insulation decisions were easy - fiberglass batts were the universal choice and using a thicker batt in a 2 x 6 wall instead of the standard 2 x4 was considered the premium upgrade.
Then in the 1990’s things got more complicated. We learned that there was more to insulation performance than the thickness of the batt: a close fit between the batt and the cavity was critical, folded insulation and overstuffed cavities were almost as bad as no insulation at all, and that sealing exterior wall, floor and roof assemblies against air infiltration was as important as insulation thickness - and in cooling climates, perhaps even more so.
This new understanding gave rise to a new generation of insulation systems, each with their own enthusiastic protagonists and detractors. How to choose? Here’s a quick overview of some of the most common options.
Fiberglass. Fiberglass floor, wall and roof insulation is still the most popular choice because of its ready availability and low price. A Grade 1 installation where each batt is cut to fit into irregular wall cavities and carefully fitted around wires, pipes and other obstructions can perform well: unfortunately most installations do not meet that standard and so do not achieve their stated R-value performance. Similarly, blown-in fiberglass attic insulation often underperforms because of its very low density, leading to a phenomenon called wind-washing.
Cellulose. Generally preferred over fiberglass by many high-performance builders, cellulose insulation made from recycled newsprint and treated with non-toxic borates to protect against vermin can be densely packed into wall cavities to help reduce air infiltration as well as insulate. It performs well as loose fill attic insulation and because of its greater density is less subject to wind-washing effects. As a recycled wood-fiber product cellulose insulation has a relatively benign environmental footprint: it provides long-term carbon sequestration and it is both recyclable and compostable. With cellulose, ceiling insulation levels of R-60 and beyond may be easily and economically achievable. Proponents point to its ability to also help stabilize a home’s humidity, while detractors point to its vulnerability to moisture damage from plumbing and roof leaks and groundwater infiltration: for this reason cellulose should not be used for basement or crawl space insulation.
Foam board products. These have been around for a long time in various forms. More expensive than fiberglass and cellulose and with a less benign environmental footprint, they are nevertheless finding favor with many green builders as exterior sheathing products where they can protect against interstitial condensation and thermal bridging. They are also commonly used for crawl space insulation because of their resistance to mold and moisture damage.
Spray foam. Spray foam is probably the most controversial family of insulation products in the market today. Its advantages are high R-value per inch and its intrinsic air-sealing properties, both of which make it especially useful in energy upgrades to certain older buildings with complicated roof and attic conditions. Disadvantages include high cost, a high environmental footprint and the need for well-trained installation crews. It is not generally economical to spray greater than about R-25 in roofspace installations which means that a whole-house performance calculation (Reschek) is needed to satisfy code requirements. Improper installation can lead to persistent odor and chronic allergic reactions from uncured chemicals in the foaming process, and the so-called ‘soy-based’ foams are not exempt from these problems. If such problems occur complete removal is very difficult - owners of historic homes should especially note that it is probably the least reversible of any insulation product.
Less common insulation options include Insulated Concrete Forms (ICF), Insulated Concrete Panel (ICP), Structural Insulated Panels (SIP), Autoclaved Aerated Concrete Block (AAC) and Straw Bale Construction. These are typically integrated constructional systems rather than interchangable components of standard wood framing assemblies. If you are considering any of these outside-the-box approaches we recommend that you work with a design and construction team which is experienced in or is prepared to fully research the critical constructional aspects of their use.