The “Almost” Passive House

Posted by on March 5, 2013 in Blog, Project, Recent, Slider | Comments Off on The “Almost” Passive House

The “Almost” Passive House

This new 3 bedroom, 2 1/2 bath home project, located in Charlotte, Vermont, was built using a modular construction approach and was designed using Passive House energy performance criteria. The goal was to meet the Passive House performance standard.  After many weeks of design work completed by Pill-Maharam architects, blasting the site,  setting the foundation and working closely with Preferred Building Systems in Claremont, New Hampshire, the 4 modules went into production and arrived on the site to be set on a beautiful, sunny spring day. Once the modules were set and the roof assembly completed, it was all ours to complete – exterior trim and siding, porches and decks, foundation parging, kitchen installation, interior window trim, flooring, etc.

Modular construction, Passive House design, net zero, high energy performance

First Module Being Set on Foundation

Passive House Foundation Details

The foundation footings were set on top of 4 inches of high density EPS foam and completed wrapped on all sides with 4 inches of EPS. The foundation had 4 inches of EPS foam installed on the exterior walls, 2 inches on the interior along with a 2×4 framed wall filled with spray foam to achieve an R-45 rating. 12 inches of high density EPS foam were placed under the slab. The wall assembly utilized double 2×4 framing with a 10 inch cavity for dense pack cellulose with 4 inches of polyisocyanurate on the exterior making the wall assembly about R-62. The flat trussed ceiling has 30 inches of loose fill cellulose for an R-value of 108. Not your typical house!

Mechanicals- Heat Pumps, Air Exchange-Heat Recovery Ventilator, Solar Hot Water, Solar Electricity

The house uses a Zehnder 350 air exchange-heat recovery system. We installed a soil exchange loop around the footings ( 2 laps of 1 inch Pex tubing filled with anti freeze) to plug into the optional Zehnder heat exchanger that pre-warms and cools incoming air and helps to dehumidify the air. The hot water system is a two panel solar hydronic system with a 80 gallon storage tank and a 50 gallon standard electric hot water heater for back up. The house is heated and cooled with a single point Mitsubishi Hyper Heat Mr. Slim FE-18 heat pump. A 3 inch concrete slab was poured and polished in the main great room as thermal mass. In the laundry area on the first floor, a condensing dryer was used to avoid having to vent to the outside creating a major penetration of the thermal envelope.

As of this posting, we have been monitoring the performance of the house closely and it has been performing quite well with overall temperature variations through the house only being a few degrees. More specific performance data will be posted in a future update. We call it the “almost” Passive House because we just barely missed certification. We were able to attain an air infiltration rate of 0.5 ACH 50 but not quite able to meet the rigorous Primary Energy Demand.

Modular construction, Passive House design, net zero, high energy performance

Modules Set and Roof Being Assembled

Passive House Design, solar hot water, double wall construction, high performance

Exterior Completed








Other Details

Fibertech windows and doors from Canada were installed through the house. Siding is local prestained hemlock and white cedar shakes on the upper gable ends. The porches were also built in post and beam style with local hemlock. The upper roof is a 30 year architectural asphalt shingle, the lower roof double locked standing seam roofing.

Inside, most of the floors are eastern white pine, concrete, tile and marmoleum. Cabinets are cherry with Vermont slate countertops and the island a large slab of joined reclaimed pine.

In the spring of 2014, a full solar electric array was installed designed to meet the full electric demand of this house with the goal of reaching net zero.


For this project we received the prestigious Efficient Vermont Best of the Best Award in 2013 along with the Vermont Green Building Networks Vermont’s Greenest Award in that same year.

Passive House Design, solar hot water, double wall construction, high performance