Terra firma Rammed Earth Project 

The project is a 2300 square foot single-story residence and detached garage with living area above, located on Salt Spring Island, BC. The building shape is unique - occupying the space created by two arcs with a radius of approximately 80'. The building walls, made of earth 2' thick, are formed using the 'rammed earth' method.

Rammed Earth Wall Structures 
Rammed earth is an ancient method of building that uses wooden forms that mold the earth to the desired shape. Dampened earth plus 10% cement is placed in the forms and tamped to total compaction. The forms are removed to reveal a solid natural wall.

Terra Firma Builders Ltd. have developed the technology to construct Structural Insulated Rammed Earth walls (SIREwall™) suitable in northern climates and seismic areas. The technology provides an earth wall with the extra strength of steel reinforcing bonded with the cement. This stabilization creates a wall that meets the highest seismic codes and has a core of foam insulation for cold or very hot climates.

Seismic Engineering
The project is located in one of the highest seismic zones in North America. Seismic engineering was a major element in the footing design, given that the walls are 24" thick, and weigh approximately 2200 pounds a running foot.

To prevent the wall turning under seismic lateral forces, the structural engineer, Greg Slakov, utilized wide footings, so that any lateral movement in the wall would be restrained by the footing width. The footing was 310' long, 11" deep, and varied in width from 5' to 6'. Where there was insufficient back fill, the footing width was increased to 6'.

Steel Requirements
The design specified four #5 steel longitudinal bars about 18" on center for lateral support. To ensure the footing will support the turning moments due to lateral seismic forces, loops of steel were installed 12" on center. #5 steel was used in hoops 24" on center, with #3 rebar hoops between each of the #5s.

Installing Fastfoot®
Meror Krayenhoff, of Terra Firma Builders Ltd., imported and compacted pit run, making it impossible to drive wood stakes into the ground. He used steel stakes instead and screw-attached 1x6 footing edge guides to the stakes. The 1x6s made it easy to form the 80' radius as required by the design. Fastfoot® was stapled to the edge guide using 3/8" staples.

Preventing Water Migration into the Footing
Terra Firma Builders Ltd. is dedicated to building healthy and sustainable structures. To achieve this, the Company installs a capillary break between the concrete footing and the ground to prevent the concrete from wicking ground moisture into the footing and rammed earth wall above. Fastfoot® not only acts as a cost effective form, but continues to add value as a damp proofing membrane to the footing concrete.