R1003.3.1

Section R1003.3.1 is titled 'Vertical reinforcing' and covers the requirements for vertical reinforcement of masonry and concrete chimneys in seismic design categories D₀, D₁, and D₂. For chimneys up to 40" wide, 4 - No. 4 continuous vertical bars must be installed; greater than 40" wide requires two additional bars per additional flue or every additional 40", or fraction thereof. Solid masonry construction has the bars installed between wythes, and hollow masonry within the cells; both methods require the bars to be grouted in place per section R606.

The model shows a chimney under construction with the first lift of grout being installed into the cells of cement blocks.