Exterior wall insulation? That usually means rigid foam and furring strips — although occasionally, it means mineral wool insulation and furring strips.
But there are other options. Two new products offer builders new ways to keep their wall sheathing warm.
InSoFast EX 2.5 insulation panels
InSoFast panels — rectangles of expanded polystyrene (EPS) foam with embedded plastic “studs” that hold drywall screws — have been around for years. The product was developed as a quick and convenient way for homeowners to insulate the interior of basement walls. The company’s original product (the InSoFast UX 2.0 panel) is 2 inches thick and rated at R-8.5.
InSoFast is now promoting a thicker panel, the , for use on the exterior of wall sheathing. (In many ways, the InSoFast EX 2.5 panels resemble the Quad-Lock R-etro system. For more on Quad-Lock R-etro, see my review in the fourth issue of GBA’s Insider magazine. GBA also lists the Quad-Lock R-etro system in our Green Products Guide.)
Each InSoFast EX 2.5 panel measures 24 inches by 48 inches by 2 1/2 inches thick. The EPS has a density of 1.25 pounds per cubic foot. The panels have tongue-and-groove joints around the perimeter that are described as “self-flashing.” While these joints are designed to shed water, the foam panels have not been approved for use as a water-resistive barrier (WRB), so builders will still need to install a layer of housewrap or asphalt felt to protect the wall sheathing.
The new 2 1/2-inch-thick panels have several features that differ from the original 2-inch panels designed for interior use:
Fastening the foam panels to a wall
While the interior panels only have to support gypsum drywall, the new exterior panels have to be strong enough to support siding. According to InSoFast president Ed Scherrer, the plastic “studs” are strong enough for this purpose, and are capable of supporting fiber-cement siding or even stone veneer.
Anyone who intends to use these panels needs to be convinced that the manufacturer has solved two problems: how to fasten the foam panels securely to the exterior of a wall, and how to fasten siding securely to the foam panels.
The vertical polypropylene fastening strips are spaced 16 inches on center. The plastic strips have an I-beam profile and extend almost all of the way through the foam panels. For the most secure installation, these fastening strips should be aligned with the home’s wall studs (a feat that can be tricky, especially after the sheathing has been covered by housewrap). If the installer is successful at lining up the plastic fastening strips with the hidden studs, the foam panels can be fastened to the wall studs with long framing nails (installed with a nail gun) or long ring-shank nails. “If you are nailing the panels up in cold weather, the polypropylene fastening strips get brittle,” Scherrer told me. “The nails can shatter the plastic strip. So if you are installing the panels when temperatures are below 50 degrees, you should switch to screws.”
Fastening each plastic strip to a stud will only work if the home’s studs are spaced 16 inches on center. If the home has 24-inch-on-center framing, you’ll only hit a stud every 4 feet.
According to the manufacturer, you really don’t have to fasten the panels to the studs unless you are installing very heavy siding. For most types of siding, the foam panels can simply be attached to the OSB or plywood sheathing. “For an adhered stone application, you want to hit the studs when you fasten the panels,” Sherrer told me. “But for lap board siding, you don’t have to. You can just fasten the InSoFast panels to the sheathing. It’s no different from attaching siding or furring strips to the OSB face of a SIP.”
If the plastic fastening strips don’t line up with the studs, you have two options: you can either attach the panels through the fastening strips to the OSB sheathing, or you can attach the EPS foam to the studs with long screws and EIFS washers. (Or presumably, you could do both.)
Fastening siding to the foam panels
Once the foam panels are secure, the siding needs to be attached to the vertical polypropylene fastening strips with screws or nails. InSoFast has released when fasteners are installed to the plastic strips. Frankly, I’m not qualified to comment on the report. However, I have no doubt that siding is being successfully attached to these panels.
At this point, InSoFast panels are most likely to be adopted by builders who don’t mind installing a product that hasn’t obtained all of the approvals that a conservative builder might prefer. Scherrer to me, “HardiPlank sent reps out to see an installation. Their instructions say that when installing HardiPlank over foam, you are limited to one inch of foam. Hardie hasn’t come out with a letter saying that they will stand behind InSoFast, but they haven’t disapproved it. The HardiPlank reps had no problems with it.”
Although InSoFast may not yet have approval letters from siding manufacturers, this product has a lot going for it. Because the foam has integral drainage channels, you end up with a rainscreen installation. This approach appears to be a good way to add R-10 to the exterior of a wall without the need to install furring strips.
If these InSoFast panels are installed on homes with 2×4 walls, they will work in all climate zones. However, if the building has 2×6 walls, these foam panels will only work in Climate Zones 5 or in warmer climates. In Climate Zone 6, rigid foam installed on the exterior side of 2×6 walls needs to have a minimum R-value of R-11.25; this value jumps to R-15 in Climate Zones 7 and 8. (For more information on this topic see Calculating the Minimum Thickness of Rigid Foam Sheathing.)
Drainage channels and wiring chases
Some observers may wonder whether the drainage channels on the back side of the foam will undermine the foam’s thermal performance. (Conceivably, convection through the channels might introduce cold exterior air between the wall sheathing and the foam.) I think that any reduction in thermal performance will be insignificant, and the channels provide an important benefit — a drainage path for any moisture that finds its way behind the rigid foam — that outweighs the very small thermal penalty. In any case, such drainage channels are common on almost all EIFS installations.
The panels have one other quirk — apparently a leftover from the original panels that were designed for the interior side of basement walls: The panels have wiring channels. As builder Mike Guertin has noted, “The wiring channels are great for basement work but not very useful for exterior use. They may be a thermal defect … Too bad they don’t offer a model without the channels. I suppose users can squirt in some expanding foam to fill some or all of each channel to block energy-robbing convection.”
The manufacturer of InSoFast panels sells the product directly from ; the advertised prices include shipping anywhere in the U.S. In small quantities, the panels cost $3 a square foot; the price drops to about $2 a square foot if you order at least 800 square feet.
DuPont Tyvek ThermaWrap R5.0
DuPont has come out with a new type of water-resistive barrier (WRB) that consists of Tyvek housewrap bonded to a fluffy, squishy quilt of insulation. Called , the odd-looking product is 1 1/2 inch thick — unless you compress it, of course, in which case its thickness is reduced to about 1/8 inch.
The 1 1/2-inch-thick fluffy insulation looks like fiberglass but is less itchy. It consists of a mixture of polyester and polyolefin fibers. It feels like quilt stuffing, and compresses quite easily.
The product is sold in rolls that are 4 feet wide by 40 feet long. It includes flaps of housewrap at the sides and bottom to make it easier to lap. It is designed to be installed with long cap nails. The material is cut with shears or a carpet knife. To prevent window flanges or window trim from compressing the thick housewrap, DuPont recommends that builders install 2x4s on the flat, “picture-frame” style, on the exterior of the wall sheathing around each window rough opening.
If the product can be installed so that the insulation remains 1 1/2 inch thick — in other words, if the siding can be installed in such a way that the insulation isn’t compressed — then it’s supposed to have an R-value of R-5. The manufacturer’s installation instructions advise, “When installing cladding fasteners, do not compress the DuPont Tyvek ThermaWrap R5.0. Compressing the product will reduce the thermal resistance.” Good luck with that.
In spite of my initial cynicism about the likelihood that vinyl siding installers can end up with a co-planar result when installing vinyl over a fluffy pillow, it may not be as hard as it sounds. According to Jim Ash, a business development manager at DuPont, “The installers have to use longer fasteners. They are nailing by hand. They constantly look at their work, and they back nails out and they drive nails back in as they see fit. They’ve been able to do it so that the results are acceptable.”
One advantage of this product compared to rigid foam: it’s vapor-permeable. If water ever gets past the Tyvek into the plastic insulation fibers, the water will drain or will be able to dry outward as well as inward.
ThermaWrap R5.0 isn’t cheap. DuPont says that the product will cost about 15% or 20% more than regular Tyvek plus 1-inch-thick rigid foam.
This is the second product called “ThermaWrap”
Tyvek ThermaWrap R5.0 is the second product in the ThermaWrap line. Tyvek’s first ThermaWrap (about to be renamed “ThermaWrap LE” to distinguish it from ThermaWrap R5.0) had a disastrous 2006 launch that was marred by exaggerations and false claims.
The first ThermaWrap product was a low-emittance housewrap that, when installed adjacent to a 3/4-inch air space, can raise the R-value of the air space from R-1 to R-2. When the product was released in 2006, DuPont claimed that the housewrap is an “insulating” membrane that is capable of “shrinking thermal bridges” and that the product “changes the dynamics of heat flow across the entire wall system, and dramatically helps improve the insulating value of the wall system.” None of these claims were true.
Not all sidings will work with ThermaWrap R5.0
At this point, DuPont is promoting the use of ThermaWrap R5.0 for use behind vinyl siding and brick veneer. The product can’t be used behind wood lap siding, fiber-cement siding, or stucco unless some type of vertical furring strips are first installed underneath the quilt. DuPont plans to introduce a new product called Insulated Battens to make it possible to use ThermaWrap R5.0 behind these other siding types. Although the design of these Insulated Battens has not been finalized, the battens will probably be made of plywood bonded to a layer of XPS, and will measure about 1 1/4 inch thick by about 2 inches wide. Insulated Battens won’t be available until “mid-year 2014.”
DuPont provided a sneak advance peak at their Insulated Battens at the International Builders’ Show in Las Vegas. Below is a video showing Matt Risinger and Mark LaLiberté discussing ThermaWrap R5.0 and the new Insulated Battens. [GBA is grateful to Matt Risinger for allowing us to share his video with our readers.]
Vinyl siding manufacturers haven’t approved it yet
Although DuPont advises builders that they can install vinyl siding over their new quilted housewrap, neither the Vinyl Siding Institute nor any manufacturer of vinyl siding has yet approved the use of ThermaWrap R5.0 under vinyl siding.
CertainTeed does not allow its vinyl siding to be installed over rigid foam that is thicker than 1 inch. CertainTeed’s installation instructions warn, “Continuous foam insulation systems (e.g. rigid insulation, structural insulation products) thicker than 1 inch create a condition where CertainTeed vinyl siding and polymer shakes cannot be properly attached to the existing framing members, steel studs, or structural sheathing.”
DuPont’s new quilted housewrap is not rigid foam. But builder Mike Guertin points out that these instructions “imply that the vinyl can’t hang off unsupported nails greater than 1 inch from the nail base.”
If this product is used under vinyl siding, what happens when you lean against the wall? Well, the wall will feel a little like a pillow; it will compress about an inch, and will spring back when you remove your shoulder. When I asked Jim Ash about this phenomenon, he responded, “You are correct. If you are leaning or pushing on the siding, it compresses and then recovers its thickness within seconds or minutes. I’m not concerned about it, and we haven’t received any objections to it.”
How do you attach brick ties?
Although DuPont recommends the use of ThermaWrap R5.0 behind brick veneer, the quilted housewrap complicates the installation of brick ties. DuPont advises builders to nail brick ties right through the housewrap, compressing the insulation underneath. That approach raises two new questions: Will the corners of the brick ties cut the Tyvek, causing leaks? And what happens to the product’s R-value when the insulation is compressed under the brick ties?
According to Jim Ash, “It’s true that brick ties have sharp corners and can potentially cut the Tyvek if the brick ties are installed incorrectly. The solution is to install the brick ties so that you don’t cut the Tyvek. And if the Tyvek is damaged, use the recommended repair procedure.” Ash says that DuPont’s calculations show that a wall assembly with ThermaWrap R5.0 and brick ties will still have a whole-wall R-value of R-5, as long as the mason “doesn’t go crazy with the brick ties.”
To me, DuPont’s new quilted housewrap seems like a peculiar product which is unlikely to gain acceptance at many job sites — but I’ve been wrong before. Time will tell.
Martin Holladay’s previous blog: “All About Furnaces and Duct Systems.”