Maximum stack heights
BCSI-B4 (BCSI booklet, SBCA/TPI) sets the maximum stack height for construction materials on trusses:
- Gypsum board: 12 in.
- Plywood or OSB: 16 in.
- Asphalt shingles: 2 bundles.
- Concrete block: 8 in.
- Clay tile: 3-4 tiles.
The traps: 12 in belongs to gypsum board, not plywood or OSB, and 8 in belongs to concrete block. The 24 in figure is not in the table at all.
Reading a stack against the table
"At the maximum" is allowed; only over the maximum violates B4. A 12 in stack of gypsum board, a 16 in stack of OSB and 2 bundles of asphalt shingles each sit exactly at their limits and are allowed. A 10 in stack of concrete block exceeds the 8 in limit and is the violation.
Brace first, then load
BCSI-B4 allows stacking only after the trusses are restrained and braced under BCSI-B1/B2.
The trap: loading trusses as soon as they are set on their bearings, on the theory that the weight steadies them. It does not. This is the classic error.
Where and how long
Two more B4 rules:
- Location: stack over bearing points. Stacking at midspan instead is a listed common error.
- Time: stacking is generally limited to about one week, unless the building designer, truss designer or truss manufacturer says otherwise.
The trap: "after bracing, for as long as the job needs" ignores the roughly one-week guideline. The full correct statement is braced per B1/B2 first, over bearings, for about a week unless the designer or manufacturer allows longer.