The Kay Hybrid combines the best features of two building systems: rubble-filled bags up to windowsill height and a lightweight frame above made with whatever is most practical.
Earthbag building is extremely adaptable. Bags or tubes can be filled with various materials and stacked like large building blocks. Among the various fill materials that can be used is concrete rubble from collapsed buildings. This concept has great potential for places such as Haiti that is currently overwhelmed with rubble.
There is a tremendous amount of rubble available — so much that it is blocking roads and hindering reconstruction. Instead of trucking the rubble away and disposing of it, why not use it to build affordable housing? Utilizing this abundant local resource would cut building costs, save transport, and create jobs by turning a waste product that’s in the way into much needed housing. (One year after the quake, over one million people are still homeless.)
Up until now, this rubble has primarily been used for rubble trench foundations, gabions and road construction. It has not been recommended for earthbags because sharp edges on the rubble could cut the bags. But after studying images on the Internet I’m convinced the rubble could be screened to 1” minus and used as bag fill. This is do-able because much of the concrete in Haiti was pulverized in the earthquake. Although this idea is experimental, and since I’m not Haiti, I would like to explore this possibility with someone who’s building there.
Suggested method for making rubble bags (subject to further tests):
- Search for piles near the building site that contain mostly pulverized rubble.
- Separate large pieces of rubble and save for other uses (urbancrete, mortared rubble walls, paths).
- Screen remaining rubble down to about 1”.
- Use screened material to make rubble bag foundations for lower courses until you’re above the level where moisture will cause problems. Be careful not to overtamp and tear the bags. Only
- light tamping is needed to settle the contents. And always double-bag foundation courses — one bag inside the other — for added strength.
- Use typical soil-filled bags for remainder of walls for increased stability or build a lightweight wall system above windowsill height.
Building full height rubble bag walls is not recommended, since they would be less stable than earthbags filled with clay/aggregate content. But low height rubble bag or gravel bag walls up to one meter are no problem with adequate reinforcement. In seismic areas, it is best to put vertical 1/2” rebar pins 2’ on center. Put pins opposite each other — one pin on each side of the wall — and tie firmly together with poly or nylon twine or cord that’s placed between bags as they are stacked. Add two strands of 4-point barbed wire between each course. Wrap the entire wall with plaster mesh in seismic areas and attach to the rebar. Fishing net or plastic mesh works well because it won’t rot in wet climates. Pour a 6” reinforced concrete bond beam at windowsill height. Embed anchors in the concrete for attaching upper walls.
Additional uses for rubble:
- Use medium and small sized pieces for rubble trenches
- Raise the site if necessary using rubble fill
- Build the floor on a base of rubble (example: soil cement or a 2” cap of concrete)
- Use rubble bags for benches and stairs
- Add screened rubble to improve characteristics of heavy clay soils
Note: some groups in Haiti have had difficulty obtaining good fill soil for earthbags. Most earthbag fill has about 25-30% clay and 70-75% aggregates. Typical subsoil is usually fine. However, sometimes the soil in Haiti is mostly rocks, and trucked in soil is ridiculously high. Filling lower courses with screened rubble can solve this problem.
In order to help rebuild Haiti we’ve modified one of our house designs for rubble bag walls. This new Kay Hybrid design (see image above) is based on our Transitional L Kay design. The kay is the most common house style in Haiti. Both versions provide immediate shelter and ease of expansion. But the Kay Hybrid starts with two rooms and a broad porch in front. Future rooms are added in the back. This is the opposite approach of the Transitional L Kay that starts with the rooms in the back.
The Kay Hybrid combines the best features of two building systems: rubble or gravel-filled bags up to windowsill height and a lightweight frame above made with whatever is most practical – bamboo, recycled wood, even straw/clay or vetiver/clay. This creates a strong, flood resistant base, speeds construction, improves ventilation and reduces plaster work. This method keeps the weight low in the wall for improved earthquake resistance. It also eliminates the need for clay soil, which can be difficult to find and expensive in some places.