Building Roofs With Vigas

An alternative to strapping vigas is to anchor them with rebar through pre-drilled holes at opposing angles (Fig. 9.13a & b).

Rafters and vigas designed for low-pitched, flat roofs can be anchored from above by building a parapet. Old adobe buildings used this strategy as a means to anchor vigas and prevent uplift by placing weight on top of the logs. This technique is still used in many countries without the addition of concrete bond beams (Fig. 9.14).

and 3/4"poly pipe

9.12: Assembly of banding (strapping) tools. Tensioner, 1,300 feet (390 m) of strapping (600 lb capacity), crimps, and crimping tool cost about $130. Compare this to the cost of a concrete beam.

9.13b

9.13a

9.13b

9.13a

9.13a: Attach viga to velcro plate. Anchor plate to wall with 3-inch long galvanized nails. Pre-drill holes at a 20-degree angle through viga and velcro plate. Drive rebar 12 inches (30 cm) deep into bag wall. If the earth has cured, pre-drill into the earth using a bit one size smaller than the size of the rebar. Pour concrete glue into the hole and tap in rebar (this will help keep the earth from fracturing). Nail halos of barbed wire onto velcro plates in between vigas.

9.13b: Lay in the next row of earthbags.

Flat roof with parapet walls and canales.

Flat roof with parapet walls and canales.

wood box cmaJe lined with galvanized sheet metal

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