Vermont Modular Builder Shoots for Net Zero

A modular unit frame sits in VerMod's Wilder, Vermont, factory bay on a freezing February day. Units take about a month to construct, according to VerMod founder Steve Davis.

An OSB panel serves as the top plate for the bodular unit's double-wall construction, minimizing thermal bridging across this framing juncture. Here, a worker applies a bead of adhesive sealant to the wall plates.

A worker in the VerMod plant applies the OSB top plate to a unit's 10-inch-thick double stud wall. The thin OSB plate minimizes thermal bridging at this location. "Optimum Value Framing" methods are used throughout the unit's shell, according to VerMod executive Chet Pasho.

This cutaway wall framing comparison, created by architect David Pill (Pill-Maharam Architects), shows the advanced framing details (right) employed in the VerMod modular units. Allthough the VerMod units are the same length and width as the HUD-Code trailers they replace, their double-stud walls with airtight detailing drastically reduce the energy consumption of the product in service.

This photo provided by Peter Schneider of Efficiency Vermont shows the interior face of a double-stud VerMod wall under construction. Super-insulated construction with minimal thermal bridging gives the wall system drastically improved performance, compared with traditional house-trailer construction.

This photo supplied by Peter Schneider of Efficiency Vermont shows the double-stud wall assembly from the exterior viewpoint. Taped ZIP sheathing serves as the air pressure boundary for the structure, as well as the drainage plane.

This photo supplied by Peter Schneider of Efficiency Vermont shows the wall top plate of the VerMod unit at a corner. OSB gussets laid flat on the wall top connect the inner and outer 2x4 plates, minimizing thermal bridging at this location.

VerMod exec Chet Pasho explains the use of a company-devised insulation density sampling device, cut from a section of vent pipe. The teeth on the end of the tube allow the inspector to bore into the insulated wall and extract a measured volume of insulation, which is then weighed to calculate density of the material as installed. Walls are tested at several points during construction to ensure uniform quality of insulation density.

VerMod's Chet Pasho demonstrates how wall insulation core samples are weighed on a digital scale to ensure uniform density of the insulation application.

VerMod founder Steve Davis stands in the open-plan kitchen-livingroom of a recently completed unit. "It's a thousand-square-foot two-bedroom, two-bath ranch house," he says. To Davis' rear is a duct chase that supplies fresh conditioned air to a bedroom and bath.

A view of the indoor head of the 9000-Btu Mitsubishi Mr. Slim mini-split heating and cooling unit for the 1000-square-foot VerMod unit. The Mr. Slim is the home's primary heat during the cold part of winter. In swing seasons, a heat pump booster on the building's "Conditioning Energy Recovery Ventilator" (CERV) carries most of the heating or cooling load.

Steve Davis in the mechanical room of the modular dwelling. A three-component system incorporating three different heat pumps serves the unit's needs: There's a Mitsubishi mini-split for primary heating and cooling, a heat-pump water heater, and a heat-pump-boosted Conditioning Energy Recovery Ventilator (CERV) that maintains air quality and distributes heat and fresh air to distant rooms.

Steve Davis demonstrates the function of the remote control unit for the building's Conditioning Energy Recovery Ventilator. Once charged at the wall, the control can be unplugged and used anywhere in the building.

The CERV's "black box" sensor and control system continously monitors CO2 levels, VOC levels, and temperature in the occupied rooms, and implements air exchange as needed to keep air quality within parameters selected by the occupant.

A tractor-trailer unit from Field and Sons (Grantham, New Hampshire) rolls out of the VerMod factory parking lot on a winter morning as Steve Davis stops traffic on Vermont Route 10 and serves as ground guide. The team has to wait until 8 AM, after school buses have finished their routes, to hit the highway with their police escort from the Windsor County Sheriff's Department. The VerMod units are considerably heavier than HUD-Code homes, and require a beefed-up trailer.

After a 96-mile highway trip, the VerMod home makes its turn off the road into the driveway of a trailer park in Shelburne, Vermont, under the watchful eye of Steve Davis.

Steve Davis and Tyler Boice place a lumber ramp in front of the trailer wheels in order to help the modular unit get past a curb as the rig exits the roadway and enters a driveway.

Under time pressure to get his rig through an awkward spot, Steve Davis crawls under the trailer to place a wooden ramp so that the trailer bed can clear an roadside obsttruction.

Steve Davis hustles to keep up with his VerMod high-performance modular unit as the tractor-trailer rig carrying the home pulls into the driveway of the mobile home park.

The truck driver and ground guide for Field and Sons (Grafton, New Hampshire) work together to get the rig pulling the heavy modular unit through snowbanks next to the narrow driveway of the mobile home park.

Steve Davis guids the truck and trailer carrying the modular unit into the moblie home park.

Tyler Boice unbolts the modular unit base from the trailer rig after arriving at the home site.

Steve Davis works with the ground crew for the crane company to ready the spreader bar, clevices, and cable for lifting the modular unit and placing the home onto its foundation.

Steve Davis guides lift cables for the modular unit into place.

Crew members connect the modular unit to its lifting cables in preparation for setting the house.

Steve Davis places a protective lumber bumper to keep the lift cables from damaging the brand-new home's eave overhang.

Crane crew members work on hooking up the lift cables.

As a ground guide works the tag line, the crane lifts the heavy modular unit off the trailer. From this point of view you can see the taped ZIP Sheathing underside of the trailer, which forms part of the unit's air-tight high-performance envelope.

The crane lifts the 70-foot-long unit off its trailer and swings it slowly toward its intended location on the new foundation.

The team watches as the crane maneuvers the heavy modular unit toward the foundation, working around streetlights, wires, and trees.

Crew members work to view the unit from all angles as the crane negotiates the path to the foundation.

Peter Schneider of Efficiency Vermont passes signals to the crane operator as the team carefully eases the 70-foot house onto its stemwall foundation.

Crew members pass signals and haul tag lines as the crane cautiously maneuvers the unit around ground obstructions.

The crane eases the modular unit down into position on the stemwall foundation.

Steve Davis pulls the unit into line with the foundation as the crane lowers the building a few final feet toward the foundation sill.

The crew applies bituminous polyethylene vapor barrier tape to the underside of the unit frame before lowering the home onto the treated wood sill.

Crew members push to line the unit up with the foundation as the crane lowers the building through the last few centimeters.

Ground crew members for the crane operator congratulate each other on the successful outcome of a tense and tricky operation.

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