New Opening in a 1925 Unreinforced Brick Bearing Wall
A three-story 1925 apartment building has 8-in. unreinforced clay-brick exterior bearing walls and wood joists at 16 in. o.c. spanning 14 ft to an interior steel beam; the joists bear about 4 in. on the brick at each floor. The owner wants a 10-ft-wide, 8-ft-high opening cut in the street wall to connect to a new retail addition, and a 4,000-lb condensing unit set on the existing roof framing. The building is in a high-seismic region (SDC D) and the jurisdiction enforces the International Existing Building Code. The contractor has proposed a single 2-in. steel angle lintel with 6-in. bearing on each side, sized from a supplier's catalog table, and wants to start cutting on Monday.
1. What must be verified and done before a saw touches that wall? Identify the load-path, concealed-condition, and sequencing issues, and explain what the 4-in. joist bearing tells you.
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Confirm the wall is actually carrying what you think it is. Walk the basement and the floor above and confirm joist direction and bearing; a 4-in. bearing is at the low end of what wood joists are allowed on masonry. That the joists bear on this wall means the wall is a primary gravity element, and it also means the joists are depending on the exact masonry you are about to cut away. Look for offset framing, a sistered beam, or a wall that is actually curtain wall before you assume bearing.
Find the concealed conditions. A 10-ft zone in a 1925 street wall can contain a chimney flue, a chase, a bond beam, shelf angles, or a previous opening that was bricked in. Open a test panel or use GPR before demolition; do not accept a drawing.
Shore first. Install temporary shoring of the joists on both sides of the opening, sequenced with the cut, and set crack monitors on the wall above. Cut in short lifts, not with a single saw cut top to bottom.
Check the load path below. The opening converts a continuous wall into two piers; the footing under each pier now takes a concentrated load. Verify footing width and condition, and check that the new point load does not overstress 100-year-old brick at the bearing.
2. Evaluate the proposed lintel. Is a single 2-in. angle with 6-in. bearing adequate? Show an order-of-magnitude check.
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Load the lintel actually carries. Take the wall above the opening: two stories of 8-in. brick at roughly 80 psf of wall area, about 18 ft of height, gives roughly 1,450 plf, plus finishes and any joists framing into the wall at the opening. Do not take credit for arching action unless the masonry is sound, bonded, and you can justify it under the masonry code; in a 100-year-old wall with unknown mortar, arching is an assumption, not a design.
Order-of-magnitude check. Effective span = 10 ft clear + 2 × 6 in. bearing = 11 ft. M = wL²/8 = 1,450 × 11² / 8 ≈ 21,900 ft-lb ≈ 263,000 in-lb. With Fb ≈ 24 ksi for A36, required S ≈ 11 in³. A 2-in. angle has a section modulus on the order of 1 in³ - an order of magnitude short. A W10×15 or W12×14 class of member is the starting point, then check deflection (L/600 is a common criterion for masonry above) and shear.
Bearing is also wrong. Reaction per side ≈ 1,450 × 11 / 2 ≈ 8,000 lb plus lintel self-weight. On a 6-in. bearing × 4-in. angle leg, that is about 335 psi - above a defensible allowable bearing for old, variable brick. Use 8 to 12 in. of bearing on a bearing plate sized to keep the stress well below the allowable, and check the masonry just below the plate for local crushing.
Detail it. The lintel must be positively anchored to the masonry, with the wall above tied to it - a loose bearing shelf is not a connection.
3. The building is in SDC D. What does that change about this scope, and how does the existing building code frame the decision?
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The wall is probably part of the lateral system. In a 1925 URM building in SDC D, the street wall is very likely a shear element. Removing 37 percent of a wall line's length over one bay removes in-plane shear capacity and creates a slender pier with reduced out-of-plane capacity. Before the opening is approved, the design professional must determine whether the remaining piers can carry the story shear, or whether the lateral system needs to be supplemented.
The IEBC, not the new-building code, governs. The work is an alteration under the IEBC. The relevant questions are (a) whether the scope crosses the substantial-alteration threshold, which brings in broader structural upgrade requirements, and (b) whether the alteration makes the structure less compliant than before. Cutting a shear wall generally does the latter, which triggers evaluation and possibly mitigation.
SDC D also brings URM-specific requirements for out-of-plane anchorage of the wall, parapets, and joist bearing. Since the joists are already being disturbed at the opening, that is the moment to install the anchorage rather than to restore a 4-in. bare bearing.
Practical answer to the contractor: do not start Monday. Mobilize the investigation, shoring design, and lateral evaluation first; then the opening, lintel, and anchorage can be detailed as one package.