How Many Shingles for a 30x40 Pole Barn Roof?
Roofing squares needed
13.9 squares
A 30 by 40 foot pole barn at a 4/12 pitch with ten percent waste.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Building length30 ft
- Building width40 ft
- Roof pitch, rise per 12 in4 /12
- Waste allowance10 %
- Ridge length, 0 if unknown40 ft
Roofing squares needed13.9 squares
| Footprint area | 1,200 sq ft |
|---|---|
| Slope multiplier at 4/12 | 1.05 x |
| Actual roof surface | 1,265 sq ft |
| Squares before waste | 12.6 |
| Squares with 10% waste | 13.9order to this number |
The material list this produces
| Shingles, bundles (3 per square) | 42 |
|---|---|
| Synthetic underlayment, rolls (10 sq each) | 2 |
| Starter strip, linear ft | 156 |
| Ridge cap, linear ft | 40 |
| Drip edge, linear ft | 140 |
| Roofing nails, lb | 31 |
Roof pitch compared
Pitch is the number most people guess at, and it is worth more shingles than any other input. Same house, five pitches.
| Roof pitch | Roofing squares needed |
|---|---|
| 4/12 | 13.9 squares |
| 6/12 | 14.8 squares |
| 8/12 | 15.9 squares |
| 10/12 | 17.2 squares |
| 12/12 | 18.7 squares |
What else matters here
Twelve hundred square feet of barn at 4/12 is 1,265 square feet of roof, just under fourteen squares with waste. The low pitch is typical for a post frame building and keeps the multiplier down, but it also puts the roof close to the bottom end of what asphalt shingles are rated for.
Most shingle manufacturers allow 2/12 as an absolute minimum and require a doubled underlayment or a self adhering membrane below 4/12. At exactly 4/12 you are at the boundary, so read the wrapper: an installation that ignores the low slope requirement is an installation with no warranty.
The other question on a barn this size is whether shingles are the right product at all. Metal panels are the default for post frame buildings because the purlin spacing suits them, they go on faster over an open frame, and they do not need a solid deck. If the barn has no sheathing, shingles are not an option without adding it.
What this calculator assumes
- Footprint times the slope multiplier gives the actual roof surface. A 6/12 roof is 11.8 percent larger than the ground it covers, which is the number most people forget.
- Three bundles per square is standard for both three tab and architectural shingles. Check your brand, a few premium lines run four.
- Synthetic underlayment is figured at 10 squares per roll, starter and ridge cap at one linear foot per foot.
Questions people ask
How many bundles of shingles for a 30x40 pole barn?
About 42 bundles at a 4/12 pitch with ten percent waste, which is 13.9 squares.
Can you put shingles on a 4/12 pole barn roof?
Yes, but most manufacturers class anything under 4/12 as low slope and require a doubled underlayment or an ice and water membrane over the whole deck. At exactly 4/12 you are at the edge of the standard method.
Are shingles or metal better on a pole barn?
Metal is the usual choice, because post frame buildings have purlins rather than a solid deck and metal spans between them. Shingles need continuous sheathing, which is an extra layer of cost and labor on a building that does not otherwise have one.
The roofing calculator takes any dimensions you like and hands back the same list.