New Home Blog  

Elizabeth and I are embarking on a project to build a new home here in Libertyville. One of my friends suggested that I write a blog of the project, keeping track of the things we looked at and the things we ultimately did. So, here is a running commentary on our efforts. I will update as significant steps in the process are completed.

We decided that we needed to demolish our home and rebuild when our basement walls and foundation were ruined by a flood, on top of a recently revealed carpenter ant infestation. We were considering a renovation of the home, but the renovation costs would be comparable, if not somewhat more, than a rebuild and we’d still have some of the space issues we currently deal with. On top of that, the home is not all that well insulated (it’s over 100 years old) and we expect energy costs to continue increasing.

Because of the expected increase in energy costs, we decided that we’d look into building formats that could reduce our dependency on traditional forms of energy sources (electrical, gas). If built well, some housing formats can reduce energy bills by up to 90%! We also wanted to be ecologically considerate in the demolition of our old home, so we will most likely do a deconstruction of our house. In addition to the ecological aspects of deconstruction (the building materials are given to charity for reuse), there are tax savings that come with the donation.

With respect to the construction of a new house, there are a number of formats that can be used but here are the three that we seriously considered.

Our research began with the idea of a Passive Solar house. A Passive Solar format relies on bringing in sunlight to heat and partially illuminate a house. An obstruction-free southern exposure is necessary.

A Passive Solar house contains significant mass (solar or thermal mass) that absorbs heat from the sun in the winter during the day and releases the heat during the evening. This mass is usually a concrete floor on the 1^st story and can be up to 10 inches thick. There is some attention paid to insulating the home but it is not the major focus of the technology. Because of the need for significant mass, a basement, which would need to support the heavy 1^st story floor, is typically not included in the house. The thermal mass is insulated from the underlying ground which will act as a heat sink (which is why basements tend to be colder than the rest of a house). Heat from the thermal mass would be transferred throughout the house by convection and from ductwork imbedded the thermal mass and throughout the house. Air passed through the ductwork in the thermal mass picks up heat and is circulated throughout the house for heating. Heat lost from the house overnight would be replaced by heat during the next day. Because sunny days in winter are not always guaranteed, a Passive Solar house would include a wood-burning fireplace or stove as a supplement to the sunlight, further reducing commercial energy dependence. The Passive Solar house is designed such that the overhang from the eaves blocks out the summer sun (which is high in the sky) but would not block the winter sun (which is low in the sky). Such a house would rely on passive cooling techniques during the summer months (e.g. block the summer sun during the day, open the windows at night).

The concept of a super-insulated house is the format for the Passive House. This format was developed in Europe and has become the standard building format for several European countries.

A Passive House has very thick wood frame walls (8 – 16 inches) filled with packed cellulose for insulation. Once completed, Passive Houses undergoes rigorous engineering tests to certify for for air-tightness, energy use, and insulating properties. A house is considered a Passive House only after it passes this certification. Builders and architects typically undergo training to certify for Passive House construction (there is a Passive House Institute in Urbana IL). Final certification requires that the trainee actually build a certified Passive House. Because a Passive House is very air-tight, it is important to have an air-handling system that can bring fresh air into the home. This is typically done by using an earth tube which pulls air in from an external vent, through a long underground tube, then into the home. When running through the underground tube, the air equilibrates to ground temperature (at about 55° year round, you can understand why uninsulated basements can get pretty cold). The cooled air is then passed through an air-to-air heat exchanger whereby the house’s outgoing stale warm air transfers its heat to the incoming cool air to help maintain temperature in the house. Because the incoming air is always 55°, the system is more efficient than attempting to heat up winter air or cool down summer air.

The windows used are highly resistant to heat transfer (compared to single-pane windows) and should be limited in size and number depending on location in the house. It is not unusual for a Passive House to use a thermal mass to assist in heating the house in winter. Again, an open southern exposure is needed for the mass. The super-insulated format preempts the need for a furnace or boiler to heat the home. As in a Passive Solar house, a Passive House with a thermal mass does not have a basement (although this is changing). Another potential drawback to any super-insulated home is that a fireplace with a chimney is taboo. A fireplace is an extraordinary breach of the thermal envelope of the house. Although there are fireplace formats that can be accommodate, the fireplace quickly warms a super-insulated house to uncomfortable levels.

Insulated concrete forms (or ICF’s) can also be used to construct a home that is super-insulated. ICF’s are hollow rectangular styrofoam molds that are ultimately filled with concrete. The molds are set one on top of another (literally like Lego blocks) to build the walls of a house, braced, then filled with concrete. The width of the interior of the forms can range from 4 to 10 inches, with 6 inches being a typical width. There is 2.5 inches of styrofoam on either side of the concrete.

Struts within the forms (or steel strips inserted into slots in the molds) provide "studs" into which nails or screws can be driven to put up drywall (inside) and siding (outside). This technology is not considered for use in a Passive House, probably because the insulating property is not as good as the format used by Passive Houses and because of the ecologically unfriendly nature of styrofoam. However, ICF’s are commonly used for super-insulated home construction because there is no official training or certification necessary to use them. There are many ICF brands but there are three basic types of ICF’s that are defined by the final structure of the concrete inside them – monolithic (or flat wall), waffle, and pillar-and-beam (or screen grid).

The waffle and grid forms were developed to reduce the amount of concrete needed (up to 20%). Overall, there is about a 10% strength difference between the strongest structure (monolithic) and the weakest (pillar and beam). All three formats utilize rebar to strengthen the concrete. As with many construction technologies, it is more important that builders use the format with which they are most experienced rather than use the format that will be cheapest (after all, you’d be spending 20% more on concrete for a 10% gain in strength if you went with monolithic over a grid). Although styrofoam itself is not considered ecologically friendly, the styrofoam used in ICF’s is expanded rather than extruded and, thus, does not used volatile organic compounds in its production. Since the styrofoam in encased within a house, it is not readily released into the environment. Unlike wood-framed walls, ICF’s are less attractive to wood-eating pests and more resistant to water damage and fire.

We investigated a number of "green" technologies to use in our house. They include:

• Earth tube
• Solar panels (photovoltaic or PV)
• Solar thermal
• Geothermal

The earth tube was discussed above. One story we heard about the earth tube was about a homeowner who wished to hide the external intake pipe. So, he planted lilacs around it thinking that it would effectively hide the pipe. In the spring, the lilacs bloomed and the scent was brought into the home through the tube. He then planted additional aromatic plants around the intake pipe so that throughout the summer, the scents of flowers permeated his home.

Solar panels have been around for quite awhile and are evolving into more efficient and (slowly) more affordable technology. They are available in many forms, from large panel arrays set on brackets to flexible shingle-like forms that can be laid on your roof like standard asphalt shingles. From a recent electricity bill, I got our daily kWhr (kilo Watt-hour) usage and used that value to determine what it would cost us to use PV to supply that amount of electricity, and how long it would take to recoup the cost through savings. With government discounts (both state and federal), I determined that it would cost about $55,000 for the system and it take close to 26 years to recoup the investment. Another problem is that we have several very large trees that block the house on the south side. Shadows on a PV array can short out a portion of the array, reducing its effectiveness. We are thinking that we’ll make our house PV-ready but not invest in the technology just yet!

Solar thermal technology uses the sun to heat water for the house. There are basically two formats – tube and plate (or panel). They both work the same way but utilize different construction to achieve the same end.

Since there are no electric currents generated, shadows on the array don’t have such a deleterious effect on hot water production. The technology is relatively inexpensive and costs can be recouped within 5 – 7 years. Unfortunately, the trees that shade the south side of our house may prevent us from using this technology.

Geothermal technology for houses uses a similar strategy as the earth tube.

Tubing that contains a heat-transfer substance (air or a glycol-water mix; usually the water mix is used because its heat transfer property is more efficient) is laid out in the ground in one of several possible configurations. The water mix in the tubes equilibrates to ground temperature (55°) as it travels through the tube and is brought into the home by a heat pump. A heat pump is like a reversible air conditioner such that it can provide cooling or heating, depending on the direction of the circulating liquids inside it (i.e. imagine physically turning an A/C window unit around to blow cool air out in the winter). When used for cooling, freon in the heat pump efficiently transfers heat from the air in the house to the water mix which is then pumped through the tubing to release the heat into the ground. The process is reversed for heating. The freon pulls heat from the water mix and transfers it to circulating air in the home. Freon is pretty cool stuff. Because a water-based geothermal heat pump is so efficient, the costs of the system can be recouped within 5 years.

Up next, contractor or architect first?