A successful earth construction project starts with proper foundations. All electrical, mechanical, and plumbing elements must be installed in the sub-grade before the slab floor is poured. It is very important, therefore, that all tradesmen work as a team and are aware of each other's work from the very beginning. The rammed earth walls (stabilized soils) need to be placed and supported upon engineered concrete footings. Vertical reinforcing steel extends from these footings into a bond beam at the top of the wall. The vertical steel spacing is generally #5 grade 60 rebar at 12 inches on center. The steel schedule and footings are based on the soils report and engineering data for the site conditions..

The next step is the form setting. Earth walls are only as good as the form setters and the earth installers. As earth construction becomes more popular, more and more builders are trying to enter the market, many without the experience to produce satisfactory results. Walls that are out of plumb or inappropriate soil mixtures can impede the project and increase costs. Burlington Construction has the experience and utilizes the appropriate procedures which eliminate these potential problems. All windows, doors and frame openings are built to the proper dimensions and are true and plumb.

Once the form work is completed, the reinforcing steel, bolts and hardware are installed. The horizontal steel reinforcing is generally tied to the vertical steel at twelve inches on center, with double bars at wall openings. During this phase, work must be coordinated closely with the structural engineers to insure earthquake safety compliance.

At this point, the form work is ready for the earth. The specific type of form work is determined by what stabilized earth process has been selected, the rammed earth or pneumatically impacted earth walls method. With the pneumatically impacted method, the earth/cement mixture is shot onto the form work much in the same fashion as gunite or shotcrete is used to make swimming pools. The moistened materials are shot out of a hose at high pressure. Drifts are built up in one or two foot lifts to the desired wall height. Control wires are set up outside the forms horizontally at 24 inch on center to define the wall thickness. The nozzle man/shooter becomes the most important member of the team during this phase of construction. He works on scaffolding along the formed plywood walls followed by a finisher who cuts and screeds the walls to the desired finish. Quality control of the earth/cement mixture means working only with stamped, engineered formulas approved by a building department.

If you choose the Rammed Earth process, the pre-mixed earth is placed and compacted into the two-sided wall forms with pneumatic air-driven rammers. The horizontal steel is then placed as the earth lifts are rammed to facilitate maximum compaction around the steel elements. Care must be taken during the ramming process not to damage the embedded plumbing and electrical pipes and boxes. The earth is stopped at the required bond beam thickness which is then poured in concrete. Walls are usually kept damp for a week to cure. The distinctive sedimentary striations and color variations in rammed earth walls make these new structures appear to be hundreds of years old. Walls constructed by either method are usually 18 to 24 inches thick. This fact gives an earth house it's feeling of solidity and permanence. The thick walls retain solar heat in the winter and coolness in the summer. The use of earthen walls also cuts energy use and costs. In counties like Sonoma and Napa, this feature, together with its fire-resistant properties, is one of the principle reasons for itsincreasing popularity. A visit to an earth home during a summer heat wave will quickly demonstrate most of its outstanding features.

Colors of earth walls vary from red to sandstone depending upon the earth available from the different quarries in northern California. The finished earth walls are maintenance free, fire and termite proof.

Wood stud walls should be attached to the earth walls with construction adhesive and concrete screws to minimize movement at the junction of dissimilar materials. The roof system is generally attached to 4X pressure treated mudsills that are attached to the earth wall bond beams with 5/8 inch foundation bolts at 24 inch on center. When the pneumatically impacted method is used, the mudsills need to be grouted in place to insure proper finish ceiling heights. The truss or cut roof is then attached by various Simpson clip configurations based on the engineer’s data. After the roof structure gets closed in, all other trades fall in line. It is recommended that all pneumatically impacted interior walls be plastered. Some clients have preferred keeping the natural look, but it is better to determine that after the forms have been removed. All remaining finish work proceeds generally as it would with a conventionally-built structure, but the finished building is anything but conventional. Unique, enduring, practical, reminiscent of both ancient and modern Mediterranean architecture, earth homes provide a continuing source of pride and comfort to the owner.