How to Choose the Best Insulation

Which insulation options are the best choices for your facility or building?



The Roof
Roof repairs and renovations can be costly propositions, so unless your roof is nearing the end of its life anyway, it may be worth it to save a roof insulation project for later and focus on the rest of the building first. However, if it’s almost time to replace or repair the roof anyway, it will likely be more economical to install insulation along with the new roof.

What's On the Market?

The amount of insulation options available can be staggering. Common types of thermal insulation include:

Batts, Blankets, and Rolls
Flexible, fibrous insulation that can be rolled out and cut as needed.

Fiberglass (glass wool) is a perennial favorite due to its low cost.

Mineral (rock or slag) wool has a higher R-value per square inch than fiberglass due to its higher density.

Cotton also offers higher R-value than fiberglass, but does not completely seal the cavity against air movement. Made from post-industrial recycled textiles.

Plastic fibers don’t burn readily, but melt when exposed to flame.

Natural fibers include cork, hemp, flax, wool, wood fiber, plant-based waste materials (such as nut shells or corn cobs), and other natural sources.

Loose Fill
Loose material that can be blown, packed, or poured into place.

Cellulose is made from recycled paper and absorbs more moisture than fiberglass or mineral wool.

Fiberglass loose fill can be blown or poured into place. See above.

Mineral wool – see above.

Polystyrene beads can serve as loose fill, but are notoriously difficult to control and hold static charges easily. Both EPS (expanded polystyrene) and XPS (extruded polystyrene) are available as loose fill in addition to their more commonly used rigid forms.

Rigid Panels
Stiff boards placed into cavities or affixed to existing walls.

Polystyrene – EPS absorbs water easily, while XPS offers higher R-value per square inch and greater structural strength and moisture resistance.

Polyisocyanurate and polyurethane both have high R-values per square inch, but must be covered with a building-code approved material to ensure fire safety.

Spray Foam and Foam-In-Place
Foam insulation that expands as it cures to fill wall cavities or cover walls.

Cementitious (cement-based) is nontoxic and nonflammable.

Phenolic (phenol-formaldehyde) is now only available as foamed-in-place insulation. Can shrink up to 2% after curing.

Polyisocyanurate is typically less expensive in its foamed-in-place form than in boards. Both polyisocyanurate and polyurethane are available as blocks and laminated panels in addition to liquids and spray foams.

Polyurethane is also available in blocks. Made from soy or petroleum. Similar to polyisocyanurate in R-value per square inch.


“You’re going to have to reroof the building regardless of its age if you’re adding insulation to the roof,” Hart says. “That doesn’t mean you should necessarily wait 20 years until your roof is leaking, but if the existing roof is new, the cost of reroofing may be hard to swallow.”

Thick planks of foam board, oriented strand board, spray foams, and blankets are popular choices for the roof due to their easy installation and unobtrusive nature, Hart says.

“Oriented strand boards with attached foam insulation can be attached to an existing wood roof. Then you’d put down tar paper and roofing shingles and add a ridge line vent and soffit vents,” Hart explains. “When the edges are finished off with aluminum flashing, you can’t even tell the building has been insulated. It’s a more expensive way to insulate, but insulating the roof from the outside may be the only thing you can do for architectural reasons.”

Hart points to a church in central Massachusetts as a prime example. The church maintained two buildings that were both heated with the same oil-fired boiler – one building was used only for worship services and was kept at 45 degrees F. on the frequent occasions when it wasn’t in use, and the other was used daily. Church leaders opted to start on the frequently used building, a two-story structure totaling 6,000 square feet of floor area.

The roof needed to be replaced anyway, so Hart’s team laid down polyisocyanurate foam boards and oriented strand boards with spacers before adding tar paper and shingles. The walls of the wood frame structure were filled with fiberglass loose fill (some installed from the inside and some from the outside), and polyisocyanurate boards were added to the exterior of the exposed basement walls and finished off with vinyl siding.

In two years with a similar number of heating days, the church’s oil use dropped from its pre-installation requirement of 6,000 gallons of oil to 4,700 gallons – a 21% drop across the two buildings, even with one left uninsulated. The church’s leaders were so impressed with the savings that they hope to insulate the other building, which has about the same footprint but a 30-foot ceiling and one floor, in summer 2012. The insulation continued to pay for itself as oil prices climbed – the church paid about $2 per gallon when the project kicked off but now pays nearly $4 per gallon.

Before and After Installation
As you narrow down your insulation choices, be sure to check building codes for minimum performance standards and compare your top choices to this reference. Fire safety is an especially important concern, and meeting this standard may require special care or extra material, such as drywall. For example, closed-cell spray foams are extremely effective insulators, but spraying down too thick of a layer at once can start a fire.

“When closed-cell foams expand and cure, they release a lot of heat,” explains Hart. “If you put the material on too thick at one time, the heat gets trapped and a fire could start within an hour. It’s a high R-value per inch material, but you’re usually limited to a maximum of 3 inches of finished thickness at a time because of the heat. Open cell foam doesn’t have that limitation, but its R-value per inch is more like fibrous insulation, which is cheaper.”

Look for an International Code Council (ICC) label on the package, which will guarantee that the product meets minimum building standards, says Jay Mishra, vice president of RADCO, a testing, quality control, and inspection agency that tests construction products.

“Anyone looking for insulation is better off purchasing insulation that’s approved and has an ICC Evaluation Service listing,” Mishra explains. “If your product does not have approval, chances are you won’t be able to install it because the building official won’t permit it. If it has an ICC report, it’s been tested in accordance with standards developed over the years, so you can have a certain minimum confidence.”

After insulating, reevaluate other building systems that could be affected by having a tighter building, Osborn recommends. HVAC in particular will likely need adjustment.

“You need to consider that you’re changing the building dynamics considerably,” Osborn says. “Many times when people insulate, they realize that their HVAC system doesn’t need to work as hard. It might need to be fine-tuned to accommodate the lower load on the building.”

Even if you’re dealing with an aging building, Hart says, you can likely identify an insulation strategy that will meet the building’s needs without excessive cost.

“There’s a huge number of older buildings that need to be retrofitted for energy efficiency, and many building owners don’t appreciate the value of retrofitting,” Hart says. “There’s no building that’s so old that it can’t be retrofitted. Old buildings don’t have to be torn down – many of them are beautiful and should be preserved.”


Janelle Penny (janelle.penny@buildings.com) is associate editor of BUILDINGS.


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