Frame doors and windows in an earthbag wall with timber box frames installed as the wall goes up, and carry the bags over each opening on a temporary wooden arch form until the wall is complete and the arch is self-supporting. A pointed Gothic arch is stronger than a round one in earthbag construction.
Part of Earthbag Building
Openings in an earthbag wall are formed by building the wall around timber box frames and bridging the top with an arch or a lintel.
An Opening Interrupts The Load Path
Every opening cuts through the courses and concentrates the load that the wall used to spread evenly; the explanation of why a lintel is needed is in Doors and Windows. In an earthbag wall the frame defines the opening, and the load above is carried either on a lintel or on an arch built from bags.
What You Need
- Timber box frames sized to the opening, with a rigid cross-brace.
- A temporary arch form, a wooden semicircle or pointed arch, strong enough to carry the bags above.
- Props to hold the form in place.
- Barbed wire to continue the courses around the opening.
For arch geometry see Arch Construction and Catenary Arch, which explains how a hanging chain gives the shape with no bending stress in the arch.
Method: Frame, Build Up, Arch, Cure
Step 1: Set the frame plumb and level on the course where the opening starts, and brace it.
Step 2: Build the wall tight against the frame, tamping each bag against it and continuing the wire courses to the frame.
Step 3: Place the arch form at the opening head, propped from below.
Step 4: Build the bags over the form, keeping the courses in running bond and the joints staggered.
Step 5: Leave the form in place until the wall is complete and the arch is self-supporting. Choose a Gothic (pointed) arch over a round one, which is stronger in earthbag construction.
Step 6: Remove the form carefully, easing the props off a little at a time and watching the arch.
Common Mistakes
- Removing the arch form early. The unsupported bags sag or fall.
- Unbraced frames. Tamping pressure pushes the frame out of square.
- Loose bags at the frame edge. Fill the gaps tight to avoid cracks around the opening.
Safety
Falling bags and unsupported arches
A bag on a high arch is heavy. Never stand under an arch form being loaded or struck, prop the form against the ground and check it has not shifted after each course.
What’s Next
- Learn next: Bond Beam and Top Plate — tying the wall together above the openings
- Combine with: Domes and Arches — arches as structure