Passiv House Roof - Trusses

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Roofs

We offer two basic types of roof systems: a vented truss roof with a Sarking membrane, and the Ecocor PassivRoof​​​​​​​™. Both perform extremely well and can be tailored for different situations.


Ecocor PassivRoof™

Vented truss roofs with Sarking membrane

What is a Sarking membrane, you ask? You’re not alone. Sarking is another word for sheathing—the continuous diaphragm covering roofs and walls. A Sarking membrane is a fabric version. We install our TEEE monolithic membrane on top of braced roof trusses and cap it with strapping, creating a vented, watertight, vapor-permeable channel below the roof surface.

The Sarking membrane can be covered with ZIP roof sheathing as a base for asphalt shingles, or with 2x4 purlins as a base for our favorite roofing material, standing seam metal. For the Sarking membrane, we use Solitex Mento Plus, a product by Pro Clima of Germany. It is the toughest vapor permeable, airtight product we have found.

The economical choice is for the truss to have a horizontal bottom chord, resulting in a conventional flat ceiling, but it can also be scissor or parallel chord trusses to create cathedral ceilings.

Below the truss, we install Pro Clima’s Intello Plus membrane as the airtight layer. It is a vapor-variable product which protects against water vapor movement with a low permeance of 0.17 Perms, on the cusp of a class 1 and class 2 vapor retarder, but opens to 13.20 Perms (a class 3 vapor retarder), allowing for drying in the presence of high moisture content. The Intello is reinforced to allow it to support dense-packed cellulose. We furr the ceiling to create an 1 ½” service cavity, which also protects the airtight membrane. We tape the seams with Pro Clima Tescon Vana acrylic-adhesive tape, and tape the fasteners with Pro Clima Rapidcell tape.

Above the truss we install Pro Clima’s Solitex Mento Plus as a WRB (weather resistive barrier) and a 2 ¼” vent space composed of ¾” strapping and 1 ½” purlins, to support a metal roof. Alternatively, we can install 1 1/8” strapping and continuous ZIP sheathing to create a substrate for a shingled roof. The vent space is not only required by code with permeable insulation such as the cellulose that we use, but venting a roof allows the assembly to handle changes in moisture loading and it extends the life span of the roof cladding.

Truss Roof Specifications

The 24” raised heel truss roof is typically our most cost effective, insulated with loose-fill cellulose to a depth of 24” to 30”

U values ranging from 0.071 to 0.045 W/m²K (0.0125 to 0.008 Btu/hr ft² °F), ≈ R 80 to 120.

The truss can be shaped like a conventional gable, or it can be a mono-pitch (aka “shed roof”), low-slope (aka “flat roof”), or other shapes.

Foam free panelized roofs

Consider our PassivRoof​​​​​​​™ for situations when a sloped cathedral ceiling is desired and parallel chord roof trusses won’t work. Designed with the same parameters as our PassivWall™ , our PassivRoof​​​​​​​™ offers the highest performance available in a roof assembly. With a deep interior service cavity, an Airtight Layer well protected toward the inside of the assembly, and a deep exterior Blanket Layer,  it is also covered with our high-performance Weather Resistive Barrier and an integral vent channel.  Our PassivRoof has special connection details between panels and at the top and bottom of each panel, which allow fast and easy air-sealing and construction joint insulation after installation. The PassivRoof​​​​​​​™ is carried by either a structural ridge beam or a load-bearing wall, and can be used singly (as a mono-pitch “shed” roof) or paired to create a gable roof.

Choosing a PassivRoof​​​​​​​™ is a good choice when shop fabricating and insulating the roof is important, a deep service cavity is needed, or when the building geometry makes a truss roof undesirable. Installation is fast, and using our proprietary methods for completing the air barrier, we can achieve an airtight, watertight building envelope in much less time than constructing on site.

Panelized Roof Specifications

The International Passive House Institute has determined Ecocor’s PassivRoof​​​​​​​™ to perform with a U value of 0.065 W/m²K (0.011 Btu/hr ft² °F), ≈ R 90.

At the eave connection with the exterior wall, typically a thermal bridge, Ecocor has negative thermal bridging: Ψ=-0.029 W/mK.

At the ridge, another potential source of problems, we have designed a connection that achieves Ψ=-0.029 W/mK.