40x70 Hay Barn

This page is ordered around height and clearance, because at 40x70 the 14-foot eave limits a hay barn sooner than the plan does.

The footprint holds 6 face bays — 2 across by 3 deep — and leaves 12 feet of depth for a covered strip along the open face where a load can stand out of the rain while it is being sorted.

What distinguishes 40x70 is depth behaviour: 3 rows along 70 feet after 10 feet of circulation, with 12 feet unaccounted for at the end of the run. Plan the exit as carefully as the entrance; buildings are emptied under more time pressure than they are filled.

A 40 by 70 footprint is a clearly directional plan: 2,800 sq ft enclosed by 220 ft of wall, at a 1.8:1 length-to-width proportion. Along its 70 ft dimension it takes 4 runs of face bays at 16 ft, leaving 6 ft over — the 6 ft is where the argument about this size actually happens. A wide, shallow store trades volume for access. Almost every bale is at or near a face, which suits an operation drawing small quantities frequently rather than emptying the building over a few weeks. Sunlight through an open face degrades the outer layer of a stack, which is a siting consideration rather than a construction one.

At 40x70 the operating question is a specific one: is it better to have a shallow stack that is entirely reachable, or a deep one that mostly is not? That is a different question from the one a hay barn of another shape has to answer, and it is why this footprint is planned as a wide-face store where most of the stack is reachable from the outside rather than as generic covered area.

Span drives headroom at 40x70: 40 feet of width on a 3:12 pitch puts 19 feet over the middle and 14 feet at the walls, so where a tall item stands matters as much as how tall it is. Depth is bought cheaply and width expensively, which is why this proportion tends to be argued about before anything else.

Height on a 40 ft span is a separate decision from the 70 ft length, and it is the span that sets the frame's behavior. Raising the eave over 2,800 sq ft affects every bay along the 70 ft dimension, so the test is whether wide loading face planning genuinely needs the extra clear height or only the floor area.

Ventilation across 2,800 square feet at this height: airflow through a stack is the reason many hay barns stay open-sided; enclosing them changes how the stored crop behaves.

The storage arrangement this floor tends toward in a heavy season is a shared building holding forage at one end and equipment at the other: the two uses meet directly, so equipment stands against the stack and the stack is worked around the equipment. Dividing the 2,800 sq ft by the 15 by 16 ft face bay gives roughly 8 positions before circulation is deducted a second time for cross movement. Whether the plan keeps 8 or drops to 4 comes back to the question this footprint is really answering: is it better to have a shallow stack that is entirely reachable, or a deep one that mostly is not?

Depth arithmetic leaves a working end zone here. 480 square feet sits past the last row, which is why 40x70 tends to be planned with a covered strip along the open face where a load can stand out of the rain while it is being sorted designed in rather than added later. Interior divisions are the last decision that should be fixed, because they are the first one that usually changes.

The 10 feet of spare width runs the whole 70-foot length — 700 square feet of wall strip. It earns its keep as shelving, staging or a walking route, not as another face bay. Utilities entering on the wrong elevation quietly rewrite the interior layout.

Because bays are independent, work is parallel rather than sequential: one bay can be filled while another is being emptied, which is the operating advantage this shape buys. What is stored changes across the year, and a building sized for one material behaves differently when the next one arrives. That movement pattern, not the 2,800-square-foot total, is what decides whether the leftover 12 feet is useful here.

The 40-foot gable can carry 2 openings, one per face bay, with 10 feet of wall left for piers between and beside them — the arrangement that keeps each position independently reachable. Height is the dimension people regret; it cannot be added later without rebuilding the frame line.

The frontage is largely open or repeatedly opened, which makes weather exposure the governing question. Which direction the face points at does more for the stored material than anything about the roof.

Loader-handled from the open side, with the working face moving as the stack grows and shrinks.

At 23.3-foot nominal bays the structure works with the layout instead of against it: one face bay per bay line, walls free of awkward half-positions. Insulating later is possible; framing for insulation later is much harder.

Two-plus rows change the access question entirely. Every rear position at 40x70 needs either its own opening or an aisle, and 10 feet of spare width is what that aisle has to come from. Long spans buy flexibility that is only worth paying for if the operation actually changes shape.

Extension is cheapest along the 70 ft dimension, where each added bay repeats work already framed; widening past 40 ft is a different frame rather than a longer one. Growing to 40 by 86 adds a 5th run of face bays — useful if the constraint is face bays rather than the 6 ft already spare at the far end.

Configured as a wide-face store where most of the stack is reachable from the outside, 40x70 is judged on whether the 6 face bays it holds match the operation, and on whether the 10 feet of spare width leaves the route this mode depends on.

• Does the work need three parked lanes, or two lanes and a moving lane wide enough for equipment to pass, or does it need a second lane that this 40-foot span cannot give?
• Is the 70-foot length being bought for depth, or for the repeated bays — six to eight repeated bays, and the bay line becomes the organising device for the whole plan?
• What stack height do you plan, and can the loader place a bale above it inside the building?
• Which sides stay open for airflow, and which face the weather?

No price appears on this page. The quantities that scale an estimate at 40x70 are 2,800 square feet of slab, 34.6 cubic yards of nominal concrete, 3,080 square feet of wall cladding and 2,886 square feet of roof cladding. A wider bay is a structural decision and a longer bay is a layout decision; the two are often confused.

Frontage is expensive: door openings, a long apron and the frame at an open face all cost more per foot than a closed sidewall, and this shape maximises exactly that element.

• eave height set by handling clearance above the stack
• how many sides remain open
• the apron the loader and trailers use
• roof drainage over an open working face

• 30x40 moves the count from 6 to 4 face bays (2 across by 2 deep), which is the reason to choose between them.
• 24x50 holds the same 6 face bays but changes the leftover depth by -12 feet, which is where the difference is actually felt.
• 32x40 moves the count from 6 to 4 face bays (2 across by 2 deep), which is the reason to choose between them.

Because this footprint is planned as a wide-face store where most of the stack is reachable from the outside, the useful next reads are different from the ones a differently shaped hay barn suggests: wide loading face planning, bay separation, open face orientation.