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Garage Conversion Structural Summary at Corona city
Garage Conversion Structural Summary Project Scope This garage conversion project involves converting an existing garage into habitable space at Corona city, Riverside County, California. The work primarily includes new structural framing, slab-on-grade modifications, and lateral system adjustments to meet California Building Code (CBC 2022) standards. The design follows ASCE 7-22, ACI 301, and the National Design Specification (NDS) for wood construction. The roof and the outside stayed the same including the parking doors. Load assumptions were taken from ASCE 7-22.
Foundation & Concrete
• Footings: Minimum depth 24" below grade for exterior walls and 18" for interior.
• Allowable soil bearing: Unless noted otherwise in geotechnical report or contract documents, the allowable soil bearing capacity shall be 1,500 psf based on presumptive values per California Building Code (CBC 2022, Table 1806.2). No site-specific geotechnical report was used or referenced. The engineer defaulted to CBC Table 1806.2, which provides presumptive soil bearing capacities for standard soil types (e.g., silty sand, sandy clay, etc.). This is a standard conservative assumption for small residential remodels and
garage conversions
when no geotech study is commissioned.
• Concrete strength: 2,500 psi (normal weight, 145 pcf).
• Reinforcement: ASTM A615 Grade 60 (YIELD STRENGTH OF STEEL 60,000 PSI (420 MPA)) steel; hooks and lap splices per ACI 318.
• Concrete cover: 3" for earth-contact, 2" for exterior exposure.
• Curing: Moist-cured minimum 7 days at ≥50°F.
Framing System
• Material: Douglas Fir-Larch lumber and engineered wood (Parallam® PSL).
• Headers:
o 3½" × 9½" Parallam PSL headers at primary openings.
o Verified for 5.4 kips reaction and 13 kip-ft moment — passed at 70% utilization.
• Columns:
o 4×4 Douglas Fir No.2 supporting headers and beams.
o Compression loads up to 5.4 kips — well within 71% of allowable capacity.
• Beams:
o 4×10 Douglas Fir No.2 flush beam spanning 4'-4" — passed at 64% of allowable moment.
• Deflection Limits:
o Live Load (L/480) and Total Load (L/240) — actual deflections < L/900 in all cases.
Wind Design
Site is not in a hurricane-prone region as defined in ASCE/SEI 7-22 Section 26.2.
• Basic Wind Speed: 95 mph (Exposure Category B). Exposure B as defined in the WFCM and ASCE7-10 is as follows: “Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions having the size of single family dwellings or larger.”
• Pressure Coefficients: Cp = ±0.8 to -0.7; internal pressure GCpi = ±0.18.
• Design Wind Pressure: up to 10.35 psf (windward).
• Roof mean height: 21 ft.
• Directionality reduction factor: Kd = 0.85 (Table 26.6-1, ASCE 7-22).
• Wind Force per Direction: N–S = 17.6 kips, E–W = 19.1 kips (E–W direction controlled).
Seismic Design
• Seismic Design Category: E (per ASCE 7-22 and USGS data).
• Mapped accelerations:
o SS = 2.47g
o S1 = 0.81g
o SDS = 1.72g
o SD1 = 1.23g
• Response modification factor (R): 6.5 for light-frame wood walls.
• Base shear: 70.6 kips (calculated via ELF procedure).
• Diaphragm forces: 0.34–0.69 per ASCE 7-22 Sec. 12.10.1.1.
Being in SDC E affects how the building is detailed and connected — even if it’s a small residential remodel. The main implications are:
a. Stronger Lateral (Shear) Walls — rated shear panels, hold-downs, and anchor bolts for large overturning forces.
b. Anchorage to the Foundation — anchor bolts with specific distances and washers, uplift and sliding checks.
c. Roof and Floor Diaphragms — nailing patterns and boundary blocking to transfer seismic forces.
d. Connections Between New and Existing Structure — new framing tied into existing lateral system.
e. Material Detailing — NDS provisions, seismic-rated fasteners, clips, and straps.
Structural Detailing & Construction Notes
• Work limited to new framing and structural modifications for the conversion area.
• Existing structure not fully evaluated for lateral performance beyond the scope area.
• No cold joints or construction joints in new foundations unless detailed.
• Anchor bolts and embedment to meet ACI and AWS D1.4 welding standards.
• Contractor responsible for safety and compliance with OSHA standards.
• Drawings shall not be scaled; all field dimensions must be verified prior to construction.
Summary of Structural Performance
Component | Material | Check Type | Result | Utilization |
Header (PSL 3½×9½) | Engineered Wood | Moment / Shear | Pass | 70% |
Column (4×4 DF No.2) | Solid Wood | Compression | Pass | 71% |
Beam (4×10 DF No.2) | Solid Wood | Bending | Pass | 64% |
Foundation | Concrete 2,500 psi | Bearing / Shear | Pass | N/A |
Lateral System | Lateral System | Seismic Base Shear | Pass | Within CBC limits |
Conclusion
The garage conversion has been structurally designed and verified under ASD methodology per IBC 2024. All key framing and load-bearing members pass code checks for gravity, wind, and seismic loading. The structure demonstrates robust performance under the governing Seismic Design Category E and 95 mph wind exposure, ensuring safety and compliance for residential occupancy.