David Easton contributed to this article.

Table 1. Title 24 Compliance Calculations Using MICROPAS4 MICROPAS4 Energy Use Summary Energy use (kBtu/ft2/yr) Standard Design Proposed Design Compliance Margin Space Heating 19.71 20.73 -1.02 Space Cooling 8.59 2.18 6.41 Water Heating 4.32 4.35 -0.03 Total 32.62 27.26 5.36 General Information Floor area: 6,045 ft2 Winter outside design temperature: 31°F Summer outside design temperature: 95°F Glazing percentage: 14.5% of floor area Title 24 compliance calculations are a prerequisite to getting a residential building permit in California. To secure approval, the calculations must show that total energy use for the proposed building is less than the standard energy budget per square foot of floor area.

Two-story wooden forms show where the walls will stand after workers shoot the PISÉ mixture against them on the other side.

The two-story wall is finished and awaits installation of the windows and doors.

The just-completed PISÉ house looks as if it had been standing for decades.

The thermal storage of these walls, which were built using the Pneumatically Installed Stabilized Earth (PISÉ) process, is so significant, in terms of energy conservation, that when John Britton of BEC Associates in Berkeley ran his Title 24 compliance calculations using MICROPAS4, he found that single glazing was all that was needed for the windows and glass doors. In other words, the heat that would be lost through the windows was insignificant compared to the heat stored in the mass walls. The predicted design loads show Lipton and Daniel saving 5,000 Btu/ft² annually for heating, cooling, and water heating over a conventionally built house, thanks in large part to the mass of the walls (see Table 1).

PISÉ--Their Solution

Shooting on the Walls

For each building project, a different blend of soils and cement may be needed, depending on the composition of the native soil and what compressive strength is required to make the structure work. Generally Jankovsky mixes up a design batch that will have a moisture content of between 15%-17%. Then he rams up test samples, lets them air dry for two days, and runs unconfined compressive strength tests on the samples. Results of the tests have ranged from 750 psi to as high as 3,000 psi.

For the Lipton/Daniel residence, Easton chose a soil blend he had used successfully on other projects and was certain would satisfy the engineering requirements as well as the architect's color palette. He specified a mix consisting of 33% 3/8-inch clean aggregate, 33% fine aggregate sand, and 33% standard concrete blend sand. Nine parts of this aggregate mix were then blended with one part cement on site, and enough water was added to reach the desired moisture content.

Holding the high-pressure hose, the nozzle operator shoots out this PISÉ mix downward at a 45°angle. This angle helps to ensure that any rebound of large aggregate kicks out away from the walls. A blow hose operator follows behind the nozzle operator to clear off rebound, because if a pocket of rebound forms with no cement paste of binder around the aggregate, that pocket will not have the same strength as the rest of the wall.

"PISÉ is a violent, messy building process," says architect Kneeland. "The high-pressure hose that the PISÉ mix comes shooting out of is basically controlled by one person, who has the hose up on one shoulder and is leaning at a 20°angle." Jankovsky helps plan the spray path so that the crew won't find themselves backed into a corner. He also works to ensure that the crew is hosing on the earth uniformly, and that no low spots or Vs are developing in the wall.

The shooting of the walls at the Lipton/Daniel house took roughly three months because of rain delays. A similar-sized PISÉ building in nearby Sonoma took one and a half months with ideal weather conditions. After the shooting, the exterior walls were coated with a clear sealant to deter moisture damage.

Thermal Performance in Northern California

Northern California may not have predictable cold winter winds, but it does have cold--sometimes frosty--winter days. Supplementing the passive solar component of thermal mass and south-facing glass in the Lipton/Daniel house are efficient hydronic radiant slabs located throughout the conditioned spaces on the first and second floors.

Radiant heated floors are the only logical way to heat a high mass house. Forced air systems, with ducts and blowers, can work effectively in airtight houses with little or no thermal storage, but they don't work well in high-mass houses. The principle is similar to that which governed the energy calculation results supporting single-paned windows. That is, the mass is so great that mass temperature, rather than air temperature, is what controls the physical comfort of the occupants. It is the energy radiating directly to the occupants from the walls and floors that governs how warm or cool they feel.

High-Tech Hydronics

What makes the system especially efficient is the Tekmar indoor-outdoor controllers and the individual zone control and mixing valves. The indoor-outdoor controllers monitor the outside temperature and adjust the rate of flow of the hot water entering each zone to compensate for shifts in outdoor temperature. The zone controllers monitor the room temperatures. The heating needs of each zone in the house are automatically read and regulated every 15 minutes.

Rather than asking the circulating pumps to switch on and off as heat is needed, the mixing valves regulate the temperature of the water through the zone. This approach results not only in a more efficient use of the fuel supplying the boiler, but also in a more customized distribution of heat throughout the house. There is no overheating of spaces, and with the outdoor sensors, no lag time. Typical slab temperatures are around 81°F.

Daniel says that the house feels comfortable all year-round. "In the winter, even though all the downstairs floors are stone, the house felt cozy," she says. "On those really hot summer days, we closed our shutters in the mornings and the house was surprisingly cool. It felt fresh walking in."

Cost Is a Consideration

But for the PISÉ houses that Kneeland has worked on, that kind of cost range has been elusive. "I warn my clients that building a PISÉ house will probably cost them double what they would pay for a comparably sized stick-built house," says Kneeland. That, Kneeland explains, is because PISÉ is a new technology and there is resistance to it on the part of building departments and contractors. The costs to satisfy the unique engineering requirements are greater. And members of all the trades who aren't used to working on a PISÉ house take more time to do their work.

"But a PISÉ wall is beautiful stuff when it comes out. In a few days, you strip the forms, and the building looks like it's been there forever," says Kneeland. "It's got instant patina, right out of the box." PISÉ's thermal mass and reduced energy costs are just icing on the cake to Kneeland. "The energy savings are a bonus," he says.

What is a bonus depends on one's perspective. For homeowners, like Lipton and Daniel, who are interested in building energy-efficient homes that have minimal impact on natural resources and will also stand the test of time, a PISÉ house's aesthetic beauty may be the icing on the cake.
 
 
 

Home Energy can be reached at: contact@homeenergy.org
Home Energy magazine -- Please read our Copyright Notice