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How to Choose the Best Insulation
A poorly insulated building isn’t just an energy hog. The loss of conditioned air frequently makes it an uncomfortable place to live and work, not to mention the extra expense of heating it in the winter and cooling it in the summer.
There are a plethora of insulation choices on the market to fit any structure, space type, or climate, but which is best for your building? The answer lies in your building’s layout.
The Basement and Other Below-Grade Spaces
Concrete floors don’t typically offer many insulation opportunities unless the building owner is willing to pay for a costly floor elevation, says Gordon Hart, consulting engineer for Artek Engineering.
Walls, however, are a different story. Rigid foam boards, for example, can be added to the interior basement walls, as can fiberglass batts. However, both of these routes require you to install wood studs and then add drywall, and you may have to account for basement windows or other needs because the retrofit makes the wall thicker.
“Usually, it’s better to insulate the basement walls because the basement has pipes in it and you don’t want them to freeze,” Hart explains. “If you’re on a concrete floor, there’s not a whole lot else you can do unless you want to elevate the floor and put in insulation boards, which is an expensive way to go.”
Above-ground floors offer many more opportunities to cut energy waste with proper insulation. Your choices here revolve around factors such as:
- R-value per inch of thickness
- Expected lifetime
- Ease of installation
- Your building’s envelope and construction type (which determine how much space you can fill with insulation)
To make the right decision for your project, put your priorities in order, says Brock Osborn, business development manager for reStore, the restoration arm of cladding manufacturer Sto Corp.
“Many times there will be a space limitation on how much insulation can be added and what the desired R-value would be,” Osborn explains. “Take into consideration terminations and junctures, such as how the insulation terminates into windows, doors, and fixtures.”
Narrow down the selection further by considering cost, how the insulation is installed, and how much disruption to normal operations your facility can tolerate. Rigid insulation, such as boards made of expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate, require you to affix the insulation either to the wall or the exterior and add a surface over it.
Flexible materials like spray foam or mineral wool only require a hole in the wall so you can spray into the cavity or the walls of an empty room, such as an attic. Use extra care when spraying foam into a wall cavity – if you can’t see what’s happening, you run the risk of over-pressurizing the wall as the foam expands, potentially warping the wall.
“Mineral wool has some clear advantages in certain areas when it relates to fire, which is why it’s commonly used in exterior rainscreen wall applications,” Osborn says. “XPS and polyisocyanurate tend to have higher R-values, so that sometimes factors into the insulation selection process, but EPS is usually the lowest cost. It’s not a magical formula – sometimes it just boils down to personal preference.”PageBreak
Attics, Peaked Roof Spaces, and Top Floors
If it’s properly ventilated, an attic can be easily insulated with spray foam or loose fill. However, some older roofs were designed without ventilation in mind, which can limit insulation options. In general, well-ventilated attics and spaces under high-pitched roofs stay cooler in summer because they keep heat away from the ceiling and insulation of the room below.
“In a retrofit, look carefully at the installation. What will it take to get the insulation into the building?” Hart says. “In an attic, it’s often quite easy to use a loose fill or a pumped foam spray because it’s an open cavity and the installers can move around.”
However, if your building is of vaulted construction and has a peaked roof, your indoor options are more limited, Hart adds.
“You probably can’t use a blowing hole – it would be very difficult. It’s similar to a wall cavity, except you really need to have some ventilation at the top to prevent moisture condensation up against the roof. It’s easily done on new construction. But on an existing building, one thing you can do is install specially designed roof insulation boards.”
These are made of rigid foam insulation attached to oriented strand boards (OSB), which have 0.75-inch spacers built in. This satisfies the ventilation requirements while still improving the peaked roof’s performance. For more roof insulation choices, see “The Roof” on page 50.
Envelopes of many types are easily insulated from the outside, which minimizes occupant disruption, Osborn says.
“For exterior applications, you would generally use some type of rigid insulation so you’re not intruding on the interior space with people inside the building,” Osborn adds. “Most of the time, you’ll do an overclad, where you apply insulation and a cladding to the existing substrate.”
Lido Beach Towers, a historic beachfront development near Long Beach, NY, opted for this approach to minimize disruption to its tenants. The 184-unit structure, which was converted into condominiums in 1984, suffered from decades of neglect and “repairs” that were merely cosmetic in nature, resulting in water penetration, structural issues, increasing energy costs, and declining property values.
Sto Corp’s renovation team added expanded polystyrene from the outside in a 100,000-square-foot exterior insulation finishing system (EIFS), a lightweight, architecturally designed synthetic cladding system that combines foam plastic insulation with thin coatings in one integrated package.
The $13.9 million renovation project, which included $5 million just for the EIFS retrofit and stabilizing the substrate, also fitted the development with new windows, doors, roof, and balconies. Five units responding to an informal energy survey the following year noted a savings of nearly 42,000 kW – about 32.5% less than the previous year.
“If it’s either hot or cold and you can’t ever get the temperature right, it’s usually due to inadequate insulation and HVAC systems,” Osborn confirms. “It’s a tough balance to get these buildings right because so much of the temperature is controlled by the effectiveness of the insulation.”
Carefully consider aesthetic requirements as part of the selection process. Masonry and brick structures have no wall cavity by nature, so any insulation must be added on top of the stone, similar to a basement’s insulation needs. Foam plastic boards are an option, as with the Lido Beach condos, but they’ll cover up the stone or brick – forcing you to bridge the divide between aesthetic appeal and energy efficiency.
“If you want to preserve the appearance of the brick on the outside, then that forces you to go inside,” Hart says. “The real challenge is when you have a solid brick wall and you like the look of the brick on the outside and inside. If aesthetics dominate and no one is willing to sacrifice the appearance of the brick, you’re stuck with uninsulated walls.”
This is a particularly troublesome problem in New England and similar climates where old, poorly insulated factories have been refurbished for use as office buildings, Hart adds.PageBreak
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.
“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 (email@example.com) is associate editor of BUILDINGS.