Do homeowners care about energy efficiency? Any number of remodelers will tell you no, but others are seeing a growing concern on the part of their clients. They predict that the trend has momentum. “[Energy efficiency] is increasingly one of the driving forces in both remodeling and exterior replacements,” says Alan Lutes, owner of Alpha Remodeling, in Ann Arbor, Mich. “I think that as energy prices continue to rise, reductions in energy costs will have a bigger and bigger impact on the cost-benefit analysis homeowners make for a product."
Higher energy costs, Lutes notes, mean shorter payback periods on efficiency upgrades. State and federal efficiency improvement tax credits appeal to homeowners, too. All of which makes high-performing options more attractive to prospects who might, in the past, have focused solely on budget and aesthetics.
Great Opportunity
Windows have been part of the energy efficiency conversation for a long time. Siding, on the other hand, doesn’t typically come up. But siding replacement can be, under the right circumstances, a great opportunity to improve a home’s energy performance. After removing old siding, applying rigid foam insulation to a thinly sheathed exterior is a relatively low-cost process with potentially significant performance benefits.
“If a house needs new siding, it is an excellent time to add rigid-foam sheathing,” says Martin Holladay, editor of Energy Design Update. “We may reach a point when the gobal climate change issue and new carbon taxes, raising the cost of energy, require Americans to retrofit their houses with higher R-value walls. The time to do that is when you’re replacing the siding.”
Upgrade energy performance by adding rigid-foam sheathing under replacement siding, or by using foam-backed panels like the Crane siding shown.
Credit: courtesy Crane Performance Siding
In addition to increasing R-value, rigid-foam sheathing creates a continuous membrane around the house. If it’s installed properly, the sheathing should significantly restrict the flow of air in and out of the building envelope, improving the efficiency of heating and cooling systems.
More Options
Meanwhile, the continued development of insulated siding means that homeowners who are willing to consider vinyl have yet another option. Brought to market just eight years ago, these products come with molded foam adhered to the vinyl face of the siding. The extra material makes for a more rigid facing, which has allowed manufacturers to produce wider profiles and bigger panels. Manufacturers have continued to improve on early iterations, offering a wider variety of styles, molded backing, and interlocking design for greater stability.
“It’s a good, solid siding,” says Mark Brick, of B&E General Contractors, in Glendale, Wis. Brick most often specifies CraneBoard. “In a lot of cases, it’s lighter, so it’s not as labor-intensive. Plus, it’s longer and there are fewer seams in it.”
Lutes, who uses Alside Prodigy, says that factory-adhered products, in addition to providing extra R-value, generally perform better all around than traditional vinyl products. “Because it conforms to the profile of the siding, the siding is more rigid,” he says. “It flexes a little bit less; it’s quieter because it rattles around on the house a bit less. I believe it would be less likely to break when it is hit during cold weather because it has this backing on it.”
Though installation is generally faster than a combination of vinyl siding and insulating rigid-foam sheathing, foam-backed siding has its own challenges. One is that the foam backing doesn’t always expand and contract with the vinyl face. Manufacturers have sought to address this issue by molding the foam to the siding. Crane’s backed siding comes with a leading vinyl edge designed to fit in a pocket between the face and backing of adjoining panels.
Still, Lutes says, buckling and oil canning can be an issue unless the foam at the edge of the panel is trimmed by the installer. “A lot of that foam has to be hand-cut; that’s sort of the installer practice. People have had difficulty with buckling,” he says. “If they don’t cut the foam back to allow for the expansion and contraction of the vinyl, it is possible to get warranty calls.”
Remodelers face other challenges in installing foam-backed siding due to the thickness of the product. For one, Lutes says, it produces bigger J-channels at window penetrations, as wide as 11/2 inches compared with a standard 5/8-inch or 3/4-inch channel. “You may have some more aluminum to bend around windows or other areas, to have a big enough flashing or to have a trim detail come out away from the house farther to cover the profile of that siding,” Lutes says.
Remodelers who use backed siding say that the decision to use the product rather than to apply rigid sheathing has to do, in part, with the needs of the project as well as client preference. Brick says the surface of the home’s exterior plays into the decision: Walls that show too much wave require a thick application of sheathing. “If you nail your siding directly to something that has a lot of bellies in it, you get that roller-coaster look, and you don’t want that,” he says. Cost is a factor, too, as backed siding can cost up to 50% more than regular vinyl. Clients whose priorities are budget and aesthetics tend to prefer a thin layer of sheathing and more-affordable vinyl, Lutes says. If energy efficiency is a priority, as is increasingly the case, Lutes usually recommends foam-backed siding.
Foam and Energy Performance
Of course, the foam-backed product is only an option when the client is interested in vinyl. But even when considering vinyl only, rigid foam appears to provide better energy performance. CraneBoard, the leader in the foam-backed market, offers a value of R-4. Alside Prodigy, which Lutes uses, offers an R-value of 5. By comparison, rigid-foam sheathing generally offers a value of R-5 per inch, and the sheathing can be installed to whatever thickness is desired. Backed siding will also necessarily have gaps because the panels have seams where they join, which means it doesn’t serve to tighten the house the way foam sheathing does.
“With foam sheathing, you get a continuous layer of insulation, which will serve to tighten up the house in case of any air leakage,” says Michael Anschel, president of Minneapolis remodeling firm Otogawa Anschel. “And you also move the dewpoint outside of the walls into the middle of the foam so that any condensation that occurs occurs in the middle of the foam where there’s no opportunity for mold to grow.”
One to 11/2 inches is a standard thickness for rigid foam, but Anschel says that’s not necessarily enough. He often specs 3 to 4 inches of rigid foam, which adds R-value and ensures that the foam will push the dewpoint of the house outside the building envelope.
Building the sheathing up to that thickness, however, can lead to trouble when it comes to flashing and trimwork. “It can be tricky,” Anschel says. “We’ve ordered custom millwork that’s thicker to make up for the difference that foam leaves in there. In other applications we’ve actually put a piece of plywood behind the trim. We’ve also pulled the trim off. If the trim is still in good condition or if it’s a complicated profile, we carefully pull it off and put a rigid backer behind it so we can reinstall it.”
To help mitigate the challenges of siding over thick applications of sheathing, Lutes, the Michigan remodeler, recently started installing IsoBoard, an ultra-thin sheathing. “It’s about a 1/4-inch to 1/2-inch thick and it has an R-value that surpasses that of both the rigid-foam board and the siding with the insulation adhered to the back of the profile,” he says. “We’ve found it to be a little easier to work with, and it provides a higher insulation value, although the cost is higher than the cost of the standard rigid-foam insulation.”
Give Me Air
Another essential consideration in jobs that call for foam sheathing is the danger in restricting airflow. If the house has atmospherically vented appliances, too much tightening can create a backdraft.
“If you tear the siding off a home that previously had strong or good air exchange and you put your rigid insulation all over it and re-side it or re-stucco it, suddenly that house is no longer breathing,” Anschel says. “The air inside the house is also no longer being exchanged. You can create a really hazardous situation.”
After you sheath a house with rigid foam, conduct a worst-case depressurization test to determine whether the increased tightness has created a backdraft. If the tests find positive pressure — meaning gases can’t escape the house envelope — you have a backdraft issue that has to be addressed, either by replacing the appliances with power- and direct-vent sealed combustion models or atmospherically venting appliances with smaller exhausts.
“You can have atmospherically re-venting appliances in a house if the venting off the appliance is done properly and you don’t have a lot of large-exhaust devices in the home,” Anschel says. “So if you have a 600 cfm hood on a range, that’s pulling a lot of air out of the house. If you have a little 200 or 300 cfm fan, then that’s not as big a deal.”
Obviously, finding out at the end of a project that it’s necessary to install new mechanicals adds to the bill, so best practice calls for conducting a test before construction begins to attempt to predict the results of the post-construction test and build any necessary mechanical work into the budget.
—David Zuckerman is a freelance writer in New York.