From The Field: Our First Modular Prefab

September 11, 2017

AirtightnessEco DesignFrom the FieldGreen ArchitectureZero Energy

On a perfect late summer day we invited a bunch of friends to watch our first modular prefab house being set.

First off, some terminology: prefab is anything factory-built, so it could be trusses, walls, floors; but modular is when “chunks” of the building (or the whole thing if a tiny house) are built in the factory. We were interested in the efficiency and quality control of prefab, and with modular, we could get windows installed, rough electrical wiring, rough plumbing, air sealing (by using the Zip System for sheathing), cavity insulation, and drywall all done in the factory.  In our case, we worked with Hi-Tech Housing of Bristol, IN since they are specifically a custom modular manufacturer, No stock plans here–you just take them whatever you’re interested in building, and they help figure out how to break it into chunks that can be transported on trucks. Once the modules are ready, a “set crew” and crane operator are hired to put it together in the field.

The general contractor, Dave Himelick, had built the foundation while the modules were being manufactured (one of the big time-savers of this method). The modules were delivered the night before, and the crane arrived early. By 9:30am, the first module was set, and by 1pm, the last big box was up, and they started working on the roof.

Modules parked on the street

Crane from back yard

Inter-module electrical connections

First one! Middle of the first floor. Note structure of ceiling, oversized for transport; this does enlarge the height of the house beyond typical framing.

#2, the back. The set crew levels the modules, attaches them to the foundation and each other, and tightens with come-alongs; later the Zip seams are taped.

#4, back top; note how the roof is hinged so the module can have roof on but not exceed transport height limits.

Gable end walls placed, then overhangs put on…

…and lots of walking around while things aren’t overhead…

We came back the next morning to see how they had finished the roof overhangs, inserted missing pieces of Zip, and taped everything off.

Rough electrical, mechanical, and plumbing, and drywall, all from the factory.

ERV and air handler for Mitsubishi heat pump; this handles the second floor, and a ductless unit handles the first floor.

All the alignments were spot on–we dimension it, they build it.

As you can see, interior and exterior finishes will be field-installed…we’ll post on that when it occurs!

Check out a video of the set day below: