Air and water vapor can enter a home by diffusing through building materials or by infiltration or air leaks. In many ways a house, due to wind pressures, act like the cabin of an airplane that experiences large pressure differences inside and outside the cabin. In the case of an airplane, a poorly sealed cabin would result in a very uncomfortable and cold ride for the passengers (not to mention there would be too little air to breath). And while a house does not deal with the effects of the upper atmosphere, it does experience pressure differences that draw air in and out of a building, similar to that of the pressure difference caused by the upper atmosphere on an airplane.

Most residential construction in the US does not utilize an air barrier under the foundation, and if an air barrier is installed, it is done in a piecemeal fashion. An air barrier below the foundation is necessary, as a surprising amount of air can be drawn into the building through the soils. This is a particular concern in Maine because of radon, a poisonous gas that can pollute the air infiltrating through the foundation.

When installing the air barrier under the foundation, it is important to remove any debris that might puncture the air barrier from below and then continue to protect the air barrier through the construction process (as it is made of plastic). There are other material options for air barriers, but plastic is moisture resistant, flexible and easy to install under the foundation. In addition, it is important to have a flexible material since the air barrier will be installed under the concrete slab, and then continue up the foundation and attach to the wall panels—unlike traditional construction that discontinues the air barrier under the foundation. We have also taken special care to ensure the continuity of the air barrier, including double caulk lines and tape at all joints.

Once the underslab insulation was installed we proceeded with installing the foundation formwork, another process that was rather simple and quick. For the foundation of the building we will be using a grade beam system, similar to a slab on grade.

To create the grade beam, we used prefabricated, insulated formwork called: insulated concrete forms (ICFs). While the system costs are comparable to an ordinary wood-framed formwork, the thermal performance is significantly greater.

ICFs are made of clipped together insulated panels, in which the concrete is poured. The plastic clip system that holds the panels together also supports the rebar, holding it securely in place during installation.

The benefits of the prefabricated, clip together sections are the reduced cost and improvement of energy efficiency with fast installation.

The flowable fill discussed previously has created a quick, even pad on which a layer of high-density expanded polystyrene insulation is installed. The insulation sheets come in large sizes – 4’ x 16’ x 6” thick – making them quick and easy to install. Our total installation time with only two people involved was about an hour.

Typically a building sits right on top of a concrete foundation, without any separation from the ground. Imagine standing outside with a heavy wool coat on and no shoes — your coat is trying to keep your body warm, but you are losing a lot of heat through your feet. When you put boots on, you are separating your feet from the ground and providing a better insulation. Adding a layer of insulation on top of the flowable fill creates a barrier between the foundation and the ground. This separation provides a complete thermal and moisture break between the earth and the building’s concrete foundation, just like boots prevent your feet from getting wet and cold. Supplying the building with a highly insulated foundation allows the house to retain more heat than in a conventional construction practice where there is no separation between the house and ground.

As with any building, creating a solid foundation is important as it provides the base for the rest of the structure. In order to improve the thermal performance of the building, as well as reduce construction costs, a slab on grade foundation was designed for the prototype. Typical residential foundations consist of concrete foundation walls that are installed below the frost line on undisturbed soil or compacted gravel. An alternative to excavating and installing foundation walls below the frost line is to install a layer of rigid insulation horizontally under the entire building. This layer of insulation thermally isolates the building from the ground, as well as maintains the earth’s geo thermal heat under the area of the building, and thereby prevents frost heaves at the building’s foundation during the winter months.

To ensure the thermal performance of the foundation, we installed 6” of rigid EPS insulation under the entire building. The potential liability of installing this thickness of rigid insulation, is that the structure of the insulation can bridge over voids in the compacted layer beneath the building during the foundation installation, but then settle with the weight of the completed construction. To ensure that the substrate is completely smooth and compacted, a layer of concrete and sand called “flowable fill” was installed. This layer of highly aerated concrete is very easy to install and manipulate to create a level and fully compacted substrate. The result of these construction layers and systems is an extremely well insulated and quickly installed foundation.

Flowable fill is a mixture of coarse sand and cement that is heavily aerated to make it – you guessed it – flowable! It came out of the truck like a frothy milk shake and was easily placed inside shallow forms. When the flowable fill cures it is crumbly and easily raked or dug up which allows for fine tuning and leveling of the pad.

A layer of high-density insulation will be placed on top of the flowable fill, providing a complete thermal and moisture break between the earth and the building’s concrete footing. The combination of the flowable fill and the high-density insulation are fundamental details that provide the prototype house with a highly insulated foundation at an affordable cost.

Despite this spring’s torrential rains, excavation for the utilities and the driveway proceeded rapidly. By restricting the footprint of the utility work and quickly replacing the topsoil in disturbed areas, we prevented the site from deteriorating into an unworkable mud pit.

It was decided early on in the project to have all the utilities enter the building from below grade. Although this not the least expensive option, it has distinct advantages. The first advantage is aesthetics as we can avoid telephone and power lines connecting to the building. The second is based on the Passive House recommendation of providing one single utility service enter into the building from below grade. Having one point of entry allows for better air sealing and reduced thermal bridges at the service entry locations.

The water line leading from the street to the house is buried at a depth of 5 feet in order to protect it from freezing in the winter. Included with the water trench, we installed a 100 foot long, ½ inch diameter tube with a closed water loop connected to a water to air heat exchanger that will act as a preheat for the incoming ventilation air. Strangely enough, we have also run an additional closed water loop in the septic tank to utilize bio thermal heat exiting the building. To verify the performance of these lines, we have installed heat probes with both loops. We will be posting the performance of the house on line when it is complete- be sure to check that out.

Orange area proposed house site

The building site for the prototype was chosen for its gently rolling topography, open space and proximity to Belfast’s downtown. The three acre lot was previously used as a hay field and woodlot, but in the recent years has only been maintained as a meadow. This gently sloping landscape allows for inexpensive, low-impact construction, while the open meadow allows for predictable solar gain.

Deciding the location of the house on site is a specific task, which will impact the site’s existing ecology and appearance, as well as the home’s future use, including creating solar access, public and private spaces. Careful planning must also be implemented before construction begins to manage the impact of the site disturbance. The GO Home’s location was chosen based on conserving as much of the trees and meadow as possible, while also creating sufficient privacy for the house from the road.

Most rural and suburban homes orient the primary façade, including the main entry and windows, towards the road. While we did orient the protorype’s front door to the road for clarity for arriving visitors, we then rotated the majority of the glazing towards the south for optimal solar gain and privacy. Articulating the difference between solar and social orientation in the siting of a house requires more consideration and critical thinking, but certainly is beneficial for both.

According to Ann Kearsley, Landscape Architect of Ann Kearsley Design, paying attention to the movement of the site (earth, water, air and sun) is key to limiting the disturbance of the landscape. Ann has been working collaboratively with G•O Logic to create a low impact construction site for the prototype house (see previous blog).

During the site planning and design process we took the following elements into consideration: water drainage, existing vegetation and sunlight. Planning for, and managing storm water runoff during and after construction is critical because the building will disturb the natural flow of water of an existing site. We tried to set the building elevation in the site to minimize excavation or filling. Because the site is sloped we needed to create a level area for the building and manage the resulting water runoff. To divert the run off away from the building we created vegetated bio swales that will become a distinct landscape element. Improper management of water drainage will result in soil erosion, which becomes a problem by creating unstable soil conditions for vegetation.

Top soil is also affected by site construction. Standard building practices, such as driving trucks all over the site and stockpiling topsoil in large piles, can destroy the top soil’s organic structure. Limiting the area of construction in the planning process on the site plan and during construction with fencing is important in order to minimize the overall impact on the landscape. The top soil excavated from the house site and driveway was stockpiled in shallow piles, mulched with hat and seeded to prevent erosion. Once construction around the house is complete, the stockpiled topsoil will be re-graded around the house to complete the landscape.

Pay attention. Start by noticing. Start with the land, with the field; start with that drift of milkweed, monarch magnet; with the flattened grass ovals of deer beds; start with the lupine near the ledge outcrop, protected from the bush hog blades by the jagged stone or maybe by the mower’s annual remembering, his choosing to turn wide around that small blue stand of Maine wildflower; start with those two sentinel apple trees, remnant of an orchard row, traces of other, earlier, hands on the land. Or start with the collapsing stonewalls bounding the field,
the ashes and maples and shadblow growing up through those tumbled lines, widening trunks dismantling over generations the carefully stacked harvest of winter frosts and spring plows. Evidence of habitation: who’s been here, who’s here now. Evidence of labor: landform expressing technology and intention and, when the work stops, wildlife’s swift re-occupation.

Move. Follow the paths that rainwater takes through the field towards the woods at the bottom of the slope. Feel the topography in your gait, long strides through tall grass on shallow slopes, small stumbles when knees soften in low spots, eddies of sedges marking depressions and swales where water is held longer, draining slowly into the soil. At the edge of the woods turn around, look back up the slope to where you started, eyes now level with the road, body a register of
distance and the change in elevation. Circle the field, inscribing a path, feeling for that restful place between edge and open where structure can engage transition.

We’re introducing a building into the continuum of occupation and life on the site and, in doing so, will redirect the course of habitation and the character of this place. Our choices about where to build and how to build will determine whether any of the present inhabitants continue to make this landscape their home and whether occasional visitors might be tempted to settle down. And, as every property is part of a much larger, regional ecological matrix, our actions will also precipitate changes in the surrounding area, the impact of our presence rippling out beyond the site boundary.

Our first engagement with the site’s ecology, that complex web of relationships among plants, animals, soil, sun and water, will cause disruption and dislocation. Construction takes up space, casting shadows, interrupting water flow, and obstructing movement. We plan the construction staging to reduce this disruption, limiting crews and equipment to a small area immediately around the structure. Topsoil is removed from the building site, stockpiled in low berms, overseeded with a cover crop and kept healthy until we can re-place it around the house next spring. The site drainage pattern is reconfigured so water moves around the building and is reconnected with the existing flow in undisturbed areas downslope. We work to anticipate the site’s response to disturbance, integrating new development with existing conditions and creating opportunities to enrich and expand the ecological health and function of this landscape.

Ann Kearsley RLA, MLAUD
www.annkearsley.com

G•O Logic is currently building its 1500 Contemporary model home on a 4-acre site in Belfast, Maine, which will be completed in January.