A key element in the block-joist floor and roof system is a patented open-web steel joist with a cross section detailed to support concrete blocks. Workers set individual blocks between pairs of joists, supported on the joists' bottom flanges, then fill voids around the joists with grout. All construction is done manually, readily learned by unskilled labor. The system eliminates problems of crane access and the scaffolding, forming and shoring associated with cast-in-place concrete slabs. The manufacturer says a three-person crew can install 1,500 square feet per day. A fire-resistive system (2- or 3-hour fire rating) and a non-combustible system are available. The article also includes a detailed construction process and a table displaying the allowable applied uniform load in pounds per square foot of block-joist slabs. [keywords: block joist, floor, roof]