How Many Shingles for a 20x24 Garage Roof?
Roofing squares needed
5.6 squares
A 20 by 24 foot garage 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 length20 ft
- Building width24 ft
- Roof pitch, rise per 12 in4 /12
- Waste allowance10 %
- Ridge length, 0 if unknown24 ft
Roofing squares needed5.6 squares
| Footprint area | 480 sq ft |
|---|---|
| Slope multiplier at 4/12 | 1.05 x |
| Actual roof surface | 506 sq ft |
| Squares before waste | 5.1 |
| Squares with 10% waste | 5.6order to this number |
The material list this produces
| Shingles, bundles (3 per square) | 17 |
|---|---|
| Synthetic underlayment, rolls (10 sq each) | 1 |
| Starter strip, linear ft | 96 |
| Ridge cap, linear ft | 24 |
| Drip edge, linear ft | 88 |
| Roofing nails, lb | 12 |
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 | 5.6 squares |
| 6/12 | 5.9 squares |
| 8/12 | 6.3 squares |
| 10/12 | 6.9 squares |
| 12/12 | 7.5 squares |
What else matters here
Four hundred and eighty square feet of footprint at 4/12 is 506 square feet of roof, 5.6 squares with waste, seventeen bundles.
If a dormer or an ell puts a valley in this roof, that valley carries more water than anything else on the building and there are three accepted ways to build it. An open valley runs a strip of metal down the center with the shingles cut back either side of a chalk line, and it sheds the fastest and clears debris the best.
A closed cut valley runs shingles from one plane all the way through and cuts the other plane back over them, which is the common residential method and looks tidier. A woven valley laces both planes together alternately, which no longer works with most architectural shingles because they are too thick to lie flat. Whichever is used, a full width membrane goes down the valley first, and nails stay well clear of the center line.
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 20x24 garage?
About 17 bundles at a 4/12 pitch with ten percent waste, which is 5.6 squares.
What is the best type of valley for a shingle roof?
An open metal valley sheds water and debris best. A closed cut valley is the common residential method and looks tidier. Woven valleys do not work well with thick architectural shingles.
What goes under a roof valley?
A full width self adhering membrane before any shingles, and no nails near the center line of the valley.
The roofing calculator takes any dimensions you like and hands back the same list.