Image Credit: Katrin Klingenberg The Klingenberg wall was one of the high-R walls described by Bruce Coldham in his December 2009 article for Fine Hombuilding, “Six Proven Ways to Build Energy-Smart Walls.”
Image Credit: Fine Homebuilding At their Passivhaus in Oakland County, Michigan, Maura Jung and Kurt Jung used I-joists to frame their walls.
Image Credit: Maura Jung Many Passivhaus designers specify the use of interior OSB. Once the OSB seams are taped, the OSB layers serves as a durable air barrier as well as a vapor retarder.
Image Credit: www.bcpassivehouse.com The walls of the Fairview #1 Passivhaus in Urbana, Illinois, are sheathed with OSB on the interior. On the interior side of the OSB, a stud wall is being framed as a service cavity for electrical wiring.
Image Credit: E-co Lab
When Katrin Klingenberg designed the first single-family Passivhaus in the U.S. in 2003, she used 12-inch-deep I-joists (TJIs) as wall studs. Located in Urbana, Illinois, the house was sheathed on the exterior side of the vertical I-joists with vapor-permeable fiberboard and on the interior with OSB, which acted as an interior air barrier, an interior vapor retarder, and structural bracing. The bays of the engineered studs were filled with blown-in fiberglass insulation.
In 2007, Klingenberg explained the principles behind her preferred wall design: “OSB has a vapor permeability of about 0.8 (considered to be semi-impermeable; that’s why we use it as vapor retarder on the inside of our frame work). … The rule of thumb for designing a diffusion-open wall assembly in heating climates is, that the outside sheathing should have a minimum of five times the permeability of the inside vapor retarder … So, with the use of the bituminous-coated structural fiberboard on the outside of our wall assemblies we are just in range.”
Klingenberg used the same wall system on several subsequent projects, including two single-family homes on Fairview Avenue in Urbana, Illinois.
In 2004, I interviewed Tom Huettner, one of the carpenters who (along with Ed Sindelar) built the first Klingenberg-designed Passivhaus in 2003. Huettner explained that the wall system was “based on a German design.” Klingenberg told me that she consulted a German document (“Balloon und Platform Framing Details”) published by Weyerhauser. Because aspects of this wall assembly have roots in Germany, many American builders assume that the system is common in Europe. In fact, few European builders use the system.
After completing her house, Klingenberg went on to found the Passive House Institute U.S. Klingenberg is a frequent public speaker on the topic of Passivhaus construction techniques, so her wall details have been copied by cold-climate builders all over the United States, from Maine to Seattle.
Bruce Coldham describes the Klingenberg wall
Architect Bruce Coldham included the Klingenberg wall in an article (“Six Proven Ways to Build Energy-Smart Walls”) he wrote for the December 2009 issue of Fine Hombuilding. Coldham wrote, “Klingenberg’s walls are built with 12-in.-wide I-joists as studs. The interior sides of the I-joists are sheathed with OSB that serves as the primary air barrier. The exterior of the I-joists is sheathed with structural fiberboard, which is vapor permeable and allows the wall cavity to dry to the exterior. …
“Walls can be site-constructed as panels and tipped up with the help of a crane. However, Klingenberg prefers to prefabricate double-story panels of about 8 ft. in width and to fill the wall cavities with high-efficiency blown fiberglass (R-4.5 per in.).”
Chris Corson is a fan
A Passivhaus builder from Maine, Chris Corson, adopted the Klingenberg wall for a Passivhaus he built in 2011. He described his conversion experience in a comment posted on the GBA website: “Katrin Klingenberg was talking about wall assemblies, yada, yada, and put up this slide of an assembly that she had just used in a project of her own. As soon as I saw the slide, it was like this great epiphany. It solved literally ALL of the issues I had been struggling with. She was gracious enough to share the details with me. …
“The assembly is basically a 2×4 load-bearing inner wall … with the OSB air barrier on the outside of the wall. Thus allowing the inner third of the wall to dry to the inside, and securing the integrity of the air barrier in the middle of the wall where it cannot be damaged. The 2×4 wall is then strapped with 11 7/8-inch TJIs, creating a box-beam wall assembly that is non-load-bearing, cantilevered over and onto the perimeter insulation. Then over that is a high-perm fiberboard sheathing.”
Distributors of European membranes approve of the Klingenberg wall
An Environmental Building News article on Agepan fiberboard sheathing reported, “Albert Rooks imports Agepan through his Small Planet Workshop; Rooks told EBN that builders ‘on the hunt for a really high-R wall’ happened upon the European concept of ‘essentially reversing the wall assembly’ by moving the plywood sheathing — or … oriented-strand board (OSB) — to the interior.”
The Four Seven Five website also endorses a version of the Klingenberg wall: “In a heating dominated climate, for the most robust assembly, you want a vapor retarding airtight layer on the interior of your insulation and a windtight/airtight and vapor-open exterior.”
Another document posted on the Four Seven Five website advises that the “inboard control layer is best composed of OSB or plywood sheathing (taped with TESCON Vana), or vapor-variable membranes like INTELLO Plus or DB+.”
Variations on the Klingenberg wall
Over the years, several variations of the Klingenberg wall have been developed:
- On the interior side of the OSB, some builders use 2x3s or 2x4s to frame a service cavity; others skip the service cavity, as Klingenberg did on her first house.
- Some builders like to build load-bearing TJI walls, while other builders choose to make the service cavity wall load-bearing so that the TJI wall doesn’t bear any loads.
- Instead of framing the walls with vertical I-joists, some builders use Larsen trusses or double-stud walls.
- Instead of using fiberboard as the exterior sheathing, some builders use DensGlass, while others omit the exterior sheathing entirely and use housewrap or a European membrane to hold the insulation in place.
- Instead of using OSB on the interior side of the I-joists, some builders use plywood or a European membrane.
- Instead of using blown-in fiberglass insulation, some builders use cellulose.
Here’s what Chris Corson has to say about exterior sheathing: “We’ve done homes without exterior sheathing using an exterior membrane system called Solitex Mento Plus. This stuff is waterproof and UV-resistant. It’s simple and fast to install, and clean to work with. It does require a considerable amount of strapping. You need battens and counter-battens to keep it from bowing out. Even with all those battens, there still is some bowing.”
Examples of homes that use the Klingenberg wall
Many Passivhaus builders have adopted the Klingenberg wall, in one of its many forms:
- The Passivhaus built by Chris Corson in Maine used vertical 11 7/8-inch TJIs to hold the wall insulation, with OSB on the interior side of the TJIs and fiberboard sheathing on the exterior side.
- The Fort St. John Passivhaus in British Columbai has walls framed with 11 7/8-inch TJIs; the walls include an interior 2×4 service cavity.
- The Cross Shelburne House in Shelburne, Vermont, used TJIs as wall studs; the stud bays were insulated with cellulose.
- The Passivhaus duplex in Whistler, British Columbia used TJIs for studs and vapor-permeable fiberboard as exterior sheathing. The walls were sheathed with OSB on the interior and include a separate service cavity on the interior side of the OSB. The walls were insulated with cellulose.
- The Jung Haus Passivhaus in Oakland County, Michigan used non-structural TJIs to contain the wall insulation.
- A Passivhaus built by Sloan Ritchie in Seattle used OSB on the interior side of the building’s vertical TJI studs.
- The Pumpkin Ridge Passivhaus in Oregon used vertical I-joists to hold cellulose wall insulation; the 9.5-inch I-joists have exterior Agepan fiberboard sheathing and an OSB air barrier on the interior.
- Dan Whitmore’s Passivhaus in Seattle and the North residence in Olympia, Washington both used Larsen trusses to hold the insulation; the trusses were sheathed on the interior with OSB and on the exterior with vapor-permeable fiberboard sheathing.
Advantages of the Klingenberg system
When compared to the wall it resembles most closely — a double-stud wall with exterior OSB sheathing — the Klingenberg wall has one important advantage: it uses vapor-permeable sheathing, thereby avoiding the “cold OSB” problem.
When I asked building scientist John Straube about the strengths and weaknesses of the Klingenberg wall, he said, “Technically speaking, there remain risks of exterior sheathing wetting because of the cold-side sheathing. But using vapor-permeable sheathing goes a long way to mitigating the risks.”
Disadvantages of the Klingenberg system
The Klingenberg wall comes with a few pitfalls and disadvantages:
- The wall system is expensive.
- Fiberboard sheathing can belly outwards when stud bays are filled with dense-packed insulation.
- It’s easier to create a tight OSB air barrier on the exterior of a wall rather than the interior, because most walls have more interior penetrations.
- Unlike walls with exterior rigid foam, the Klingenberg wall system doesn’t directly address thermal bridging and air leaks at rim joists.
- Local code officials may question the use of engineered floor joists as studs.
- The wall assembly makes more sense in cold climates than warm climates or mixed climates.
Double-stud walls cost less than walls framed with TJIs
The main reason that double-stud walls are more common than Klingenberg walls is cost. When I asked Joseph Lstiburek about the Klingenberg wall, he was terse. “It’s an expensive wall,” he said. “TJIs are expensive.”
Straube voiced a similar concern. “I-joist walls are expensive,” Straube told me. “There are lots of problems: How do I attach the I-joists to the sill plate? How do I attach cladding and sheathing? And to what end? It’s easier to build a double-stud wall than an I-joist wall. I have no answer as to why. An I-joist wall has no performance benefits over a double-stud wall, and no price benefit.”
The problem of bellying fiberboard
In March of 2011, I visited a construction site in Olympia, Washington, where the Artisans Group was building a single-family house called the North residence. I spoke with Mark Dixon, an Artisans Group carpenter, who told me that the fiberboard wall sheathing they used was unable to resist the pressure of the dense-packed blown-in fiberglass insulation. After the insulation contractor finished insulating the walls, the fiberboard had bulged outward as much as 3/4 inch in some stud bays. The workers eventually managed to force the bellies back, at least partially, but the experience revealed one potential drawback of fiberboard sheathing.
Chris Corson has had similar experiences at several job sites in Maine. Corson reported, “On some projects we’ve used high-perm fiberboard for exterior sheathing. … It worked; it did its job. But it’s difficult to work with. It’s hard to install. It’s dirty. It smells like asphalt. When we started installing the cellulose insulation, it really bellied out. Fortunately we caught the bellying before it became a big problem. We finished the job by watching it closely and babysitting the insulation contractor.”
It’s easier to seal the outside of the wall than the inside
As I reported in a 2010 article called “Airtight Wall and Roof Sheathing,” many energy experts (including Marc Rosenbaum) advise builders to tape exterior OSB wall and roof sheathing to create an exterior air barrier.
Straube think that Rosenbaum’s approach makes more sense than Klingenberg’s. “The big issue is, why would you want OSB on the inside?” Straube asked rhetorically. “The answer to some of the problems [with the Klingenberg approach] is to just build another wall on the inside, so you have somewhere to put the wiring on the interior of the air barrier. This is classic European thinking by non-builders. These are people who understand the building physics. But what about the labor? What about the cost?”
Straube continued, “Why not tape up the exterior sheathing in an airtight manner? After all, there are minimum details and penetrations on the outside compared to the inside. It’s much easier to create an air barrier on the outside than on the inside. If you do it that way, there is no need for a service cavity. Really, you have to ask, what is the question that this wall is answering?”
The usual argument, I told Straube, is that in a cold climate, the best place to locate your primary air barrier is on the interior side of your wall insulation, in order to avoid convective looping in the wall assembly. “I would say that the worries about convective looping and the insistence on the need for an interior air barrier are not based on science and research,” Straube answered. “Seriously, if you are insulating with cellulose, the risk of problems due to convective looping is essentially zero. We know that the amount of air flow from convective loops is 5 times or 10 times less than the airflow associated with an air leak through the wall. I’m not saying that convective loops are nonexistent, but I’m saying that we can solve many of these problems by simply using dense insulation.”
Air leaks at rim joists
Straube is a fan of walls that include a layer of insulation (either rigid foam or mineral wool) on the exterior side of the wall sheathing. One advantage of this approach is that it addresses thermal bridging and air leaks at rim joists.
With the Klingenberg wall, “the bigger air leaks still exist,” said Straube. “You still have thermal bridging and air leakage at the floor joists. Where does air leak? Air leaks through electrical outlets and at interfaces. Fixing those problems can be done, but it doesn’t make sense.”
Using I-joists as studs raises structural issues
I-joists are designed to be installed horizontally, not vertically. According to John Straube, “I-joist walls are difficult to get past a code official. I-joists aren’t designed to resist compression. Of the three or four I-joist manufacturers in North America, none will say that their I-joists are good for vertical loads. In an earthquake, the failure of the wall will be from buckling of the webs, since they weren’t designed to take vertical loads. In Sweden, on the other hand, they build different I-joists for walls than for floors. The ones for walls are designed for compression.”
Fortunately, there is a simple way around this problem. If you frame a service cavity wall with 2x4s and 2x6s, you can use that wall to support the roof loads and to satisfy your building inspector. Then the I-joist wall installed on the exterior side of the service cavity wall doesn’t need to be load-bearing.
What about warm, humid climates?
It’s important to remember that the Klingenberg wall is a cold-climate wall. “In climate zones 4, 5, 6, 7, 8, the wall works well,” Lstiburek told me. “But in climate zones 1 through 3, you should switch the exterior sheathing from fiberboard to OSB, and use plywood instead of OSB on the interior. Even better, use plywood inside and outside. Plywood is a smart vapor retarder, varying from 1 to 10 perms.”
I asked John Straube whether the Klingenberg wall would work in Texas or Florida. “You would need to worry about what the cladding is,” he answered. “If you have a moisture-storing cladding that is not well ventilated, you could have problems, even in Connecticut. In Houston, you will routinely have a bit of a problem. We have seen problems related to this in similar applications — for example, in floors over garages. The humidity is driven inward, and the humidity releases formaldehyde in the OSB. In hot, humid climates, those risk factors go up. When this happens, the smell of hot pee in the house can be quite noticeable. That’s the urea or uric acid from the damp OSB. It doesn’t happen with exterior OSB sheathing, because the OSB tends to dry to the exterior easily. But if the OSB is on the interior side of the assembly, it stays cooler and wetter for longer.”
Old thinking from the 1970s?
The underlying principle behind the Klingenberg wall is rooted in a decades-old view of wall design. In the early days of building science, designers worried that walls got wet during the winter due to vapor diffusing from the interior towards the exterior. In the 1970s, inward solar vapor drive was poorly understood, and few homes were air conditioned.
John Straube isn’t sure why the Klingenberg wall includes interior OSB. “Why not use plywood instead of OSB?” he asked. “I guess it’s because the designers of this wall are stuck in the 1970s, and think they need an interior vapor retarder.” I told Straube that Klingenberg cited the rule of thumb requiring exterior sheathing to be five times more permeable than interior sheathing.
Straube responded, “That is just so outdated. And it is true only in some climate zones. If you install insulation on the exterior side of the wall sheathing, you get to put the airtight layer in the middle of the wall. It works in all climates, and there is no need for a special service wall, and there is no need to change the usual framing package. All I have to change is my cladding attachment details and my window installation details.”
Vapor-open sheathing is a good thing
Some features of the Klingenberg wall — the vertical I-joists and the use of interior OSB — seem more like quirks than features that deserve to be widely copied.
However, other features of the wall system deserve to be emulated. The best features of the Klingenberg wall are its inclusion of a ventilated rainscreen gap between the siding and the sheathing, and the use of vapor-permeable fiberboard sheathing instead of exterior OSB sheathing. Any cold-climate builder who designs a thick wall insulated with cellulose or blown-in fiberglass insulation — whether the wall is framed with a I-joists, Larsen trusses, or a double row of studs — should include a rainscreen and vapor-permeable sheathing.
Martin Holladay’s previous blog: “Cut-and-Cobble Insulation.”