Pole Barn Takeoff: Posts, Concrete, Girts, Trusses, Steel Square Footage, and Cost
Post count and spacing, the holes and concrete under them, the girt and purlin lines, the truss count and span, the wall and roof steel square footage with waste, and the material and installed cost on your barn.
A post-frame building is a perimeter post line at 4 to 8 ft on center, a girt line at 24 in on center, a truss at the post line, and steel on both surfaces. The takeoff runs on the perimeter for the posts and the girts, the plan area scaled by the pitch for the roof steel, and the wall area less the openings for the wall steel. Post-frame trusses are built for the post spacing, which is why a 12 ft wide truss on an 8 ft post line and a 12 ft truss on a 4 ft post line are two different trusses at two different prices.
How the math works
- Perimeter and posts: perimeter = 2 times (length plus width). Posts = perimeter divided by the post spacing, rounded up, plus 4 for the corners, the jambs, and the openings. Post length = eave height plus 2 ft of bury.
- Hole and concrete: a 12 in diameter by 24 in deep hole is 1.57 cu ft, about 0.065 cubic yards, and 2.6 80 lb bags. Multiply by the post count and add 6 percent for the spoil and the over-pour.
- Framing: girts at 24 in on center, rows = eave height divided by 2 ft, length = perimeter times rows. Trusses at post spacing, count = length divided by spacing plus 1, each at width plus 2 ft of overhang. Purlins at 24 in on center across the slope.
- Roof area: plan area times the pitch factor, which is the square root of (144 plus pitch squared) divided by 12: 1.08 at 4 in 12, 1.15 at 6 in 12, 1.20 at 8 in 12, 1.20 at 10 in 12. Wall steel = perimeter times eave height minus the openings, plus 5 percent for the laps and cuts, plus 8 percent on the roof.
- Cost band: material at 14 to 21 dollars per sq ft of plan area on a kit shell, installed turnkey at 22 dollars per sq ft on a 10 ft eave, 26 on a 12 to 14 ft eave, 31 on a 16 ft eave, with a slab at 8 to 13 dollars per sq ft, an overhead door at 1,600 to 3,800, and a 200 amp service at 2,800 to 6,500.
How many posts does a 40 by 30 pole barn need?
About 20 posts at 8 ft on center on a 140 ft perimeter, plus 4 at the corners, jambs, and openings, so 24 posts, at 14 ft post length on a 12 ft eave. At 4 ft on center the same building needs 39 posts, which is the engineered snow-load line and about 60 percent more lineal post.
How deep do pole barn posts go?
2 ft minimum at the sides of the building, with 30 to 36 in at the corners and the end posts in a frost region, a 12 in diameter hole with a bell, the post off the stone in a plastic sleeve, and the concrete crowned 2 in above grade. A heated slab needs the frost protection at the perimeter with the slab edge insulated.
How much steel does a pole barn need per square foot?
Wall steel at 1.05 times the perimeter times the eave height less the openings, roof steel at 1.06 to 1.08 times the plan area times the pitch factor, which is 1.08 at 4 in 12, 1.15 at 6 in 12, and 1.20 at 8 in 12. A 40 by 30 barn at 12 ft with a 5 in 12 pitch is about 470 sq ft of wall steel and 415 sq ft of roof steel, about 885 sq ft, about 4.4 squares with the laps, the cuts, and the overhangs.
What is the clear span limit on a pole barn?
Timber plate trusses carry a 40 to 60 ft clear span at 4 to 8 ft spacing on a shop-engineered tag, with 40 ft at 12 in spacing on a 15 in deep plate truss a common answer. Beyond that the answer is a steel frame, a glulam rafter, a rigid frame, and a post-frame building with a column line and a beam inside. A 30 ft clear span at 8 ft spacing is a 28 to 44 lb per lineal foot truss on a 30 to 70 psf ground load, and the ground load is the county number, not a guess.
What does a pole barn cost per square foot in 2026?
Material on a kit shell at 14 to 21 dollars per sq ft of plan area, turnkey installed at 22 dollars per sq ft on a 10 ft eave, 26 dollars on a 12 to 14 ft eave, and 31 dollars on a 16 ft eave. A 40 by 30 barn at 12 ft is about 1,200 sq ft, about 31,000 dollars installed on the mid band, plus a slab at 8 to 13 dollars per sq ft, an overhead door at 1,600 to 3,800, and electrical at 3,500 to 9,500.