Once at a building conference I heard about the results of a study on air quality. The study said the air quality inside the average new home in rural Wisconsin was 8 times worse than the air quality outdoors in New York City. This made my head swim. How could it be true? And then I heard more, and read more, about how toxins and pollutants can build up inside a home, and if there’s poor ventilation, reach unsafe levels in the air. Rates of asthma and other respiratory diseases have been on the rise in this country, and while industrial pollution is certainly a factor, the way houses are built and furnished is probably a bigger factor in the decline of respiratory health.

How can a home be less toxic? Conceptually it’s very simple—reduce the nasty stuff inside and bring in plenty of fresh air. Practically, though, it’s not that easy. On the material side, builders have gotten away from good old-fashioned building materials like solid wood, plaster and stone, and for some good reasons: they’re expensive and poorly insulating. But when these materials are replaced with particle board, fiberglass, vinyl, and synthetic carpets, the home buyer is spending less money and probably using less energy for heating, but at the same time volatile organic compounds, formaldehyde, and other toxins have been introduced to the interior air. And in an effort to reduce energy use, builders have been trying to make buildings more air-tight and less drafty, thereby improving comfort as well as the utility bill. However, the combination of the tighter envelope and the off-gassing interior finishes is what leads to sick people in Wisconsin (and other places).

With the advent of “sick building syndrome,” architects and builders are hopefully becoming more aware of what is being put in houses and taking steps to ventilate properly. It is now relatively easy to find out if a building material is air-quality friendly. Several ratings agencies exist to test and determine the safety of various materials; an architect can specify formaldehyde-free or low-voc plywood and paints; natural linoleum is available as an alternative to vinyl flooring; people should know better than to put carpeting in a damp basement, and so on. On the ventilation side, agencies such as the American Society of Heating, Refrigerating, and Air Conditioning Engineers studies indoor air quality and issues standards for rates of ventilation. They have formulas for determining how much air to bring into the house over time to ensure adequate fresh air supply.

More specifically, in the homes G•O Logic builds, we install a complete, ducted, mechanical ventilation system that delivers fresh air to bedrooms and living spaces and removes stale air from the kitchen and bathrooms. The incoming air passes through a heat-recovery unit that transfers almost all the heat from the outgoing air to the incoming air, which means there’s very little energy penalty for healthy ventilation. We determine the proper ventilation rate based on accepted standards. For example, in the 1500 square-foot model home, we will ventilate at a rate of 70 cubic feet of air per minute, continuously. This means the entire volume of air in the house will be changed once every 3 _ hours, ensuring healthy air quality for a family of 4 or 5. The air flow is very low and generally delivered to points in the house where it’s not noticed, so one never feels a draft. And on the material side, we specify only low- or no-voc materials and finishes. The floors are either polished concrete or solid wood; cabinets are formaldehyde-free. The building is incredibly air-tight, which helps tremendously in the energy-efficiency and comfort of the home, and when coupled with the ventilation system, results in a home that’s both super-efficient and healthy to be in.

There is a measure for the amount of air leaks, or “infiltration” that passes through a building’s shell, and it can be determined by a blower door test. The test results for this measure of infiltration can sound rather abstract, but in fact, the amount of air that leaks or infiltrates a building’s shell has a significant impact on the energy performance of the building, as well as the indoor air quality. The benefit of a well-sealed building is that fresh air can be filtered and tempered through controlled intake and exhaust ducts and continuously delivered throughout the house to ensure a healthy indoor environment.

To achieve Passive House Certification, the blower door test result measuring the air infiltration through the building shell needs to be less than .6ACH @ 50 Pascals – which is a very low and difficult number to achieve. As a reference for this level of infiltration, the average new home that is built (with attention paid to air sealing) is typically 10 ACH. Passive House requires a 90% improvement on the air sealing of its certified buildings. We recently conducted a blower door test on our prototype and were pleased to see the test results were so low that the machine did not register the amount of air leaking into the building at the standard test pressure. The blower door technician did not have a small enough aperture on his fan to measure the tiny amount of air passing through!

The approach we used to achieve this level of air sealing on our building is based on planning the air barrier for the entire building from the foundation to the roof early on in the design process. We have also chosen durable construction materials for the air barrier, that are installed and sealed early on in the construction process. We find it much easier to seal the simple raw building elements before the many layers of insulation, utilities and finishes are installed, thus avoiding the complexities that happen later in the construction sequence.

The foundation: A plastic vapor barrier was installed on the inside of the foundation that is continuous, sealed at joints, and sealed to the SIPs.

Walls: The SIPs, which are considered air barriers unto themselves, are thoroughly sealed between the panels with both spray foam and tape. Because the panels are large, the number of joints between the panels is reduced.

Ceiling: The air sealing at the ceiling is created by adding a durable layer of o.s.b. to the underside of the trusses, which is then taped at the joints to ensure air tightness. We choose o.s.b. instead of plastic for this barrier because of its durability in the construction phase and over the long term.

Doors and Windows: The last and critical element of air sealing is at the openings for the windows and doors. In these locations we sealed the rough openings much like the joints between the panels with both foam and tape. In addition to sealing to the windows and doors, it is critical to choose windows and door products that are designed to have low infiltration rates as well. We find the European multi point lock hardware creates the best air seal for window and doors, and therefore have used these products on the prototype.

The structural insulated wall panel systems (SIPs) have many advantages when creating a well-insulated and air-sealed building shell that is cost effective to produce. The panels we chose to use on the prototype are 6-inch thick urethane panels, that are 4 feet wide by 24 feet long, factory manufactured and pre-cut by Winterpanel in Vermont. The most significant advantage of the SIPs is that they provide an uninterrupted thermal barrier for the shell that is also a durable and easily sealed air barrier.

The Passive House requirements for a building’s shell are very specific. To qualify for Passive House Certification, a building should not have any thermal bridges in the foundation or building shell, and the building, when complete, must meet strict air sealing requirements verified by a blower door test. The SIPs system has allowed the prototype’s construction to conform to these Passive House requirements, while still allowing for simple and cost effective construction.

The second advantage of the SIPs system has to do with the size of the panels and the ability to have them factory pre-cut to fit each building design. These benefits are maximized by utilizing our computer designs in the actual production of the construction components. By utilizing advanced three-dimensional computer models, we are able to coordinate all the expensive building shell components (including windows, SIPs and structural frame), and then incorporate the computer’s accuracy in the actual construction process. By putting emphasis on planning and leveraging that in the construction, we can improve the speed, accuracy, and quality of the site work.

One frequently asked question regarding SIPs panels is the environmental impact of the foam insulation used in the panels. The three standard foam types used in SIPs panels are urethane foam, and Expanded Poly Styrene (EPS). We choose to use urethane foam for the prototype’s panels because it has a higher R-value per inch, resulting in a thinner panel and a higher total R-value per unit cost. The criticism of this foam type is that the R-value decreases over time. The total aged R-value of the urethane, however, is still higher than the comparable EPS R-value per unit cost. While both foam options are considered green products according to the USGBC, it has been suggested that the EPS production is more environmentally friendly of the two foams. G•O Logic has used both foam types and considers their application on a case-by-case basis.

With the grade beam footings complete, the next step in the construction process is the erection of the hybrid timber frame.

The concept behind the structural timber frame system was to create a structural system that is simple, quick to install, and easy to replicate. The structural concept also required a separation of the load bearing structural system from the thermal shell of the building, which enables greater flexibility in configuring the facades as well as reducing the potential for thermal bridges in the shell.

The thermal envelope of the building is created using SIPs (structural insulated panels) that are as large as 24 feet long by 4 feet wide and factory cut to fit the structural frame and façade. The benefit of the size of these structural panels is that they only need to be attached to the structural frame at the floors and roof, resulting in a reduced quantity of framing materials and fasteners. The use of SIPs in conjunction with the hybrid timber frame also results in a building shell that is easy to air seal and has virtually no thermal bridges.

The timbers that we choose for the structural frame at the exposed locations are locally harvested white pine, with some standard dimensional framing where the structure is not exposed. To reduce the cost of the frame, we worked closely with our structural engineer Albert Putnam to simplify the basic design and the structural connections. The details for the frame connections have been reduced to the most basic form, including butt joints, hidden metal straps, and hidden lag screws at the connections. We reduced the number of framing members to save costs, incorporating the minimum members to create a stable structure. The timber frame also relies on the SIPs panels for its lateral resistance, thereby avoiding expensive let-in bracing in the actual timber frame.

The roof structure of the building was created with a scissor truss spanning the north to south walls. The scissor truss was chosen because it is cost effective to build and install. The scissor truss also allows for the easy installation of a thick layer of blown-in insulation in the web area of the truss, easily accommodating an average of 24 inches of cellulose. The scissor truss also allows for spatial flexibility on the 2nd floor with the opportunity to create an insulated attic area, loft space of vaulted ceiling.

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.