The structural beam is the primary load-carrying element of a Broken Arrow attached covered patio — it spans between the posts that support the patio roof’s load and transfers that load to the footings below. An undersized beam that deflects excessively under load creates a visible sag in the roof structure that is one of the most common indicators of low-quality covered patio construction in the Broken Arrow market; an over-engineered beam adds unnecessary cost without improving the structure’s performance. Understanding how beam sizing works for a covered patio in Broken Arrow helps homeowners evaluate whether their contractor’s structural approach is appropriate before construction begins.
Beam Sizing Principles
Covered patio beam sizing for Broken Arrow projects: the primary beam in an attached covered patio typically spans from the home’s ledger (the structural attachment point at the home’s exterior wall) to the first row of posts, and from post to post across the patio’s width; the beam’s required size is determined by three variables — the span (the distance between supports), the tributary width (the roof area that the beam is responsible for carrying, measured from the beam’s centerline to the next beam’s centerline), and the design load (the weight of the roof system per square foot, including roofing material, sheathing, framing, and snow load where applicable in Broken Arrow). Broken Arrow’s design loads: the City of Broken Arrow uses the International Residential Code’s live load of 20 pounds per square foot for residential roof structures and a dead load of 15 to 20 pounds per square foot for a typical shingle roofing system (shingles, 7/16-inch OSB sheathing, 2×6 or 2×8 rafters at 24 inches on center, and insulation in a conditioned structure); for an open covered patio structure with no ceiling insulation, the dead load is typically 10 to 15 pounds per square foot; the combined design load for a Broken Arrow covered patio roof is 30 to 40 pounds per square foot. Span tables and species: the IRC span tables provide maximum allowable spans for different lumber species, sizes, and spacings under specific design loads; for southern yellow pine lumber (the dominant structural lumber species in the Broken Arrow market), a double 2×10 beam (two 2×10 members nailed or bolted together) can span approximately 10 to 12 feet at 15 feet of tributary width under a 40 psf design load; a double 2×12 beam can span approximately 12 to 14 feet at the same tributary width; for larger spans (14 to 20 feet), engineered lumber (LVL — laminated veneer lumber) provides greater strength and stiffness than sawn lumber at equivalent member depth. LVL beams for covered patios: LVL (laminated veneer lumber, brand names Microlam, TimberStrand, Parallam) is manufactured from wood veneers bonded under heat and pressure, producing a beam that is stronger and more dimensionally stable than sawn lumber of equivalent size; LVL does not crown, warp, or shrink after installation; a 3.5-inch by 14-inch LVL beam (3-1/2″ x 14″) can span approximately 18 to 22 feet at 15 feet of tributary width under a 40 psf design load; LVL is the standard specification for spans over 14 feet in Broken Arrow covered patio construction. For spans over 20 feet or tributary widths over 20 feet, an engineer’s design is recommended regardless of the beam species — the IRC span tables do not cover all combinations of span and load, and engineered solutions (glulam beams, steel I-beams) may be required for large covered patio structures.
Post Spacing and Footing Design
Covered patio post spacing and footing design for Broken Arrow projects: post spacing in a covered patio is determined by the beam’s maximum allowable span — if the beam can span 12 feet, posts can be no more than 12 feet apart; if the beam can span 16 feet, posts can be spaced up to 16 feet apart; increasing the post spacing allows a more open, unobstructed covered patio design with fewer posts interrupting the outdoor room’s sight lines. Post size: 6×6 posts (nominal, actual 5.5 inches by 5.5 inches) are the standard specification for Broken Arrow covered patio structural posts; 4×4 posts (3.5 inches by 3.5 inches) are permitted by the IRC for covered patio applications under specific height and load limits, but VistaScapes & Design specifies 6×6 posts as the standard because the larger post produces a more substantial visual appearance, provides greater resistance to lateral racking loads from wind, and allows larger post cap and base hardware that looks proportional to the covered patio structure. Footing size: post footings in Broken Arrow are sized to distribute the post’s load onto the soil without exceeding the soil’s bearing capacity; Oklahoma’s standard soil bearing capacity for residential construction is typically 1,500 to 2,000 pounds per square foot; for a Broken Arrow covered patio with a 12-foot post spacing and a 40 psf roof load, each post carries approximately 8,640 to 11,520 pounds at maximum load; a 24-inch diameter by 18-inch deep concrete footing (approximately 2.5 square feet of bearing area) is adequate to distribute this load at 1,500 psf soil bearing capacity; the footing depth of 18 to 24 inches below grade places the footing below Broken Arrow’s frost depth and prevents frost heave from lifting the post and distorting the covered patio structure. VistaScapes & Design designs the beam, post, and footing specifications for every Broken Arrow covered patio project and includes the structural details in the permit application drawings.
Call VistaScapes & Design at (918) 779-1317 for a free covered patio and outdoor kitchen consultation in Tulsa. We’ll design the structural system for your covered patio and include all structural details in the permit drawings.
