01What this calculator estimates
Every barndominium cost calculator on the market stops at a dollar figure. Before you can price a build accurately — or even sanity-check a supplier’s quote — you need an actual bill of materials: how many trusses, how many steel panels for the walls and roof, and how much concrete for the slab. This calculator takes your building width, length, wall height, truss spacing, and slab thickness and returns exactly that quantity takeoff.
The output is a planning takeoff, not an engineered materials list. Post-frame construction methods and truss spacing standards are documented in detail across the post-frame building industry, and any final structural design should be signed off by a licensed engineer, following the general construction-industry safety practices tracked by OSHA’s construction standards.
02Truss spacing and slab thickness — what changes the quantities
Truss spacing is one of the biggest levers on both truss count and overall structural design. Post-frame buildings commonly use 4 ft or 8 ft on-center spacing; the U.S. Census Bureau’s New Residential Construction data tracks the broader framing-material trends behind these choices as lumber and steel pricing shift year to year.
03Panels, framing, and the slab
Wall steel panels are estimated from your building’s perimeter divided by the standard 3 ft panel coverage width, since panels are installed vertically around the full perimeter. Roof panels are estimated from the building’s width divided by the same coverage width, since roof panels commonly run in one continuous sheet the full length of the building rather than in short horizontal courses. A roof pitch allowance of about 8% is added to account for the extra sloped-surface area versus the flat footprint. Structural steel and cold-formed framing products used in post-frame construction are tested against standards tracked by NIST’s Materials and Structural Systems Division.
Insulating a steel-frame shell properly matters as much as the framing itself, since steel conducts heat and cold far faster than wood — the ENERGY STAR seal-and-insulate methodology is a solid reference once your shell quantities are set. If you are also sizing electrical rough-in for the shop or garage bay, our conduit fill calculator can help.
- Enter your building width and length in feet.
- Enter your eave wall height in feet.
- Choose truss spacing: 4 ft o.c. or 8 ft o.c.
- Choose slab thickness: 4 in or 6 in.
- Press Calculate to see trusses, wall panels, roof panels, and concrete volume, plus wall/roof area and footprint.
Once you have a materials takeoff, our barndominium cost calculator turns living area and shop/garage area into a full dollar budget with the same category structure.
This is a planning-stage quantity takeoff. It does not include:
- Engineered truss design, wind/snow load calculations, or a stamped structural plan — always get a licensed engineer to confirm truss spacing and sizing for your specific climate zone.
- Trim, flashing, fasteners, and closure strips, which add to the panel count above the raw coverage-area math.
- Rebar or wire mesh reinforcement inside the concrete slab, vapor barrier, or gravel base — get a concrete contractor’s spec for your specific soil and load conditions.
- Interior framing, insulation, drywall, and finish materials — see the barndominium cost calculator for the dollar side of those categories.
Panel coverage width, truss-spacing options, and the pitch allowance reflect common post-frame construction practice, not an engineered spec for your specific building. Confirm final quantities against your truss manufacturer’s layout and your steel supplier’s panel schedule before ordering materials.
04Related calculators
Working through a related project? Try our Garage Door Spring Size Calculator, Stud Calculator, and Board and Batten Calculator.
01The formula
Truss count comes from building length and spacing; panel counts come from perimeter and width divided by standard panel coverage; concrete volume comes from footprint and slab thickness.
Where:
- length, width= building footprint dimensions in feet.
- spacing= on-center truss spacing, 4 ft or 8 ft.
- perimeter= 2 × (width + length), used for wall panel count.
- slab thickness= 4 in or 6 in, converted to feet for the volume calculation.
02Worked example
Take a 40 ft × 60 ft building, 14 ft walls, 8 ft o.c. trusses, and a 4 in slab:
This building needs 9 trusses, 67 wall panels, 14 roof panels (81 steel panels total), and about 29.6 cubic yards of concrete for the slab — a starting bill of materials to compare against a post-frame supplier’s formal quote.