A barn roof that drips along every screw line looks like it needs a new roof, and most of the time it does not. The rubber washer under each screw head, EPDM or neoprene, gives out years before the steel. Whether the building has earned a re-gasket pass, a re-screw, a panel swap, or a full re-skin comes down to the steel at the eaves, the purlin spacing, the cold-morning drip, and whether it counts as a farm building. Panel systems and pricing sit on the metal roofing page.
Barn roof leaking at the screws: new panels or a re-gasket pass?
| What you see | The fix | The number |
|---|---|---|
| Drips at every screw line, panels solid, 15 to 20 years old | Re-gasket pass: new washered screws throughout | $500 to $2,200 on most outbuildings; a big machine shed on the visit |
| Screws spinning or backed out, steel dimpled | Re-screw one size up, a #12 in the old hole | On the visit |
| Panels bent or lifted at a gable after wind | Panel swap, edge metal re-secured | On the visit |
| Rust-through at the eaves, holes in the flat, 30 to 40 years old | Full re-skin | $9,000 to $15,000, about $3 to $8 per square foot |
| Drips on a cold, dry morning, condensation rather than a leak | Ventilation, an insulation detail, or fleece-backed panels at a re-skin | Depends which |
The first row is the common one: sun breaks down the washer, a screw driven too deep bulges it out the sides, one driven too shallow never seats it. A screw line past 20 years is on borrowed time, and the re-screw spends the hole it fixes: the #10 steps up to a #12, and a hole that will not hold the #12 is no longer a fastener problem. If a purlin, the horizontal 2x board the panels screw to, has split or pulled off the truss, that gets fixed from inside first.
What the pass buys is the rest of the panel’s life: washers give out at 15 to 20 years, the pass resets that line, and solid steel runs toward 30 or 40 before rust at the eaves makes it a re-skin. The same money is well spent on a 20 year roof and wasted on a 35 year one. That range covers a shed. On a 40 by 60 machine shed the screw count is what the visit measures.
Trim moves a re-skin inside that band: a shed with three overhead doors takes more fabricated pieces per square foot than a plain gable the same size. Whether the old steel comes off or new panels go over it is a purlin and screw-hole call on the estimate visit.
What steel goes on a machine shed roof: gauge, screws, and purlins
Farm-building ribbed steel is a standard profile: 36 inches of cover from a 38-inch sheet, 3/4-inch ribs on 9-inch centers, and a siphon groove in the lap draining what gets past the rib. Central States makes it as Panel-Loc Plus, McElroy as Max-Rib, Fabral as Grandrib 3.
- Gauge. The lower number is the thicker steel: by Central States’ table, 29 gauge is 0.0150 inch at 0.704 pounds per square foot, 26 gauge 0.0185 at 0.866. About a quarter thicker, heavier for it, rated to carry more at every spacing.
- Steel and finish. Galvalume AZ50, the aluminum and zinc coating that keeps the steel from rusting, over steel with a minimum yield of 80,000 psi, finished in SMP, silicone modified polyester, a harder paint than the PVDF (Kynar) on house panels.
- Screws. #10 sharp-point metal-to-wood screws with a bonded metal-and-rubber washer, driven straight down rather than angled, in the flat beside the rib, which is what Fabral’s post-frame book calls for, though Central States allows the rib too. About 80 per square (100 square feet), every rib at the eave, ridge, and endlaps and every 24 inches between, with #12 stitch screws closing the sidelaps.
- Purlins. Fabral recommends no wider than 24 inches on center, kiln-dried 2x softwood, the screw biting at least 1 inch into the wood; green lumber twists as it seasons and loosens every screw in it. Older buildings were not all framed to it, and what a gauge carries at a wider spacing is a table number rather than a rule of thumb.
Will the purlins carry a Chippewa Valley winter? Snow load on a pole barn metal roof
The state’s design snow figure for houses is 40 pounds per square foot in Chippewa, Dunn, and Eau Claire counties and 30 in Trempealeau and Buffalo. That code is written for dwellings and does not reach a farm building, but the figure gives you a number to hold the manufacturer’s table against.
Central States’ 2010 Panel-Loc Plus guide lists allowable loads for a panel crossing three or more purlins, two numbers at every span: one for the steel breaking, one for it bending too far. The lower one governs, and it is the one quoted here. At Fabral’s 24 inch spacing, 29 gauge comes in at 112.1 psf, far past the 40 the state asks of a house. Wider spans turn up on older buildings: 29 gauge carries 49.8 at 3 feet and 28.0 at 4, where 26 gauge is 34.4, so neither clears 40 on 4-foot purlins. Those are panel numbers, before the panel’s own weight and with purlins and trusses figured separately. A roof that has stood its winters on 4-foot purlins is no tear-off on the strength of a table; at re-skin, a purlin between each pair puts 29 gauge back at 112.1.
The farm-specific problem is drifting: the state’s commentary tells designers to allow a higher load where sliding and drifting snow collects on a low roof beside a taller one. On a farm that is the lean-to off a taller machine shed: it takes the slab off the higher steel on top of what falls on it, and shows it as bowed purlins and a wavy eave. Fixing that is framing before it is panels.
Why a metal barn roof rains inside on a cold morning
Bare steel over open purlins has nothing between it and the air below, so on a cold morning the underside falls under the dew point of the air rising off cattle, hay, or a wet floor, and the roof rains on the equipment. A re-gasket pass will not touch it; there are three answers.
The first is a factory-applied fleece on the panel’s underside, Central States’ DripX, the DripStop membrane. It holds condensation in its fibers, more than a quart per 10 square feet, and releases it as the roof warms. It is bonded at the mill, so it gets ordered with the panels and cannot be added afterward.
The second is ventilation, on the livestock rule: Penn State’s freestall guidance is a ridge opening 2 inches wide per 10 feet of building width, sidewall openings at the top of both walls equal to half the ridge, and a 4:12 to 6:12 pitch. A barn closed up tight in cold weather condenses. A house attic follows a state ratio, worked out in the attic ventilation guide.
The third is for a building getting insulated: Fabral’s rule is that porous insulation never sits against the panel, and that a vapor barrier, polyethylene or 30-pound felt, keeps moisture off both the insulation and the metal, which manure, fertilizer, lime, and feed corrode from below.
Do you need a permit to re-roof a barn in Wisconsin?
For the roof itself, almost never. Wisconsin’s commercial building code exempts buildings on a farm premises used exclusively for farming, SPS 361.02(3)(e), and the state applies it building by building on a 90 percent test: the crop stored, processed, or sold there has to be at least 90 percent the owner’s own, the seed and fertilizer bound for the owner’s farms, the equipment used on that crop. A rented-out shed, a neighbor’s crop under your roof, or a hobby barn off a working farm can fail it, and one that fails sits back under the commercial code, which the state or a municipal building inspector administers, not the county.
Zoning is the county’s, and it is about where a building sits, which comes up when one is new or grows. Dunn County’s sheet lists new roofing as needing no zoning permit. Eau Claire County’s building permit page says re-roofing usually needs no building permit, and that wiring in an ag building does, without answering the zoning side. Chippewa County’s ordinance is silent on re-skinning a farm roof, so that is a call to county zoning at 715.726.7940. Around Osseo and Mondovi it belongs to Trempealeau and Buffalo counties; the roof permits guide has the towns, and the farmhouse is where the real permit rule lands.