Shingles for a 28 × 42 ft roof at 3/12, simple gable
| Bundles3 per square | 41bundles |
|---|---|
| Squares (with waste) | 13.3sq |
| Roof area1,176 ft² footprint × 1.031 pitch factor | 1,212ft² |
| Pitch factor√(1 + (3/12)²) — pure geometry | 1.031 |
| Waste allowancetwo planes, cuts only at the rakes | 10% |
| Starter shingles140 ft of eave and rake | 2bundles |
| Hip & ridge cap42 ft of ridge | 3bundles |
| Underlaymentsynthetic, 10 squares per roll | 2rolls |
| Ice & water shieldeaves, 24″ inside the exterior wall line — check if your code requires it | 433ft² |
| Roofing nails — standard4 per shingle, about 4,267 nails | 31lb |
| Roofing nails — high wind6 per shingle — required in high-wind zones and by most warranties above 110 mph | 46lb |
| Walkable3/12 can normally be walked | Yes, with care |
- Footprint width
- 28 ft
- Footprint length
- 42 ft
- Pitch
- 3 /12
- Roof type
- simple gable
Footprint is not roof area
This is where roofing estimates go wrong, and they go wrong in the direction that leaves you short on a Saturday.
A 28 × 42 ft footprint is 1,176 ft² on the ground. At 3/12 the roof over it is 1,212 ft² — the pitch factor is 1.031, which is √(1 + (3/12)²). Pure geometry, no fudge factor.
Order off the footprint and you are 0.4 squares short before waste is even counted.
Squares and bundles
13.3 squares with 10% waste for a simple gable roof — 41 bundles at three per square.
Waste is not one number. A simple gable cuts only at the rakes. A hip roof cuts along every hip. A cut-up roof with valleys and dormers throws away a fifth of what you buy, and no amount of careful planning changes that.
The two lines everyone forgets
Starter: 2 bundles for 140 ft of eave and rake. Hip and ridge cap: 3 bundles for 42 ft.
These are separate products, not field shingles cut down. Using field shingles as starter voids most manufacturers' wind warranties, which is discovered at the claim rather than at the purchase.
Underneath
2 rolls of synthetic underlayment, and 433 ft² of ice-and-water shield at the eaves — 24 inches inside the exterior wall line, which is what the IRC asks for where it applies. Check whether your jurisdiction requires it.
31 lb of roofing nails at four per shingle, or lb at six for a high-wind zone.
Two things to price before you decide it is DIY
Tear-off: about 3,667 lb of old shingle to strip and skip.
And access. Above 8/12 a roof stops being walkable for most people, and roof jacks, planks or scaffolding cost real money that belongs in the estimate before you decide this is a DIY job.
Notes
- **Footprint is not roof area, and the gap is bigger than people expect.** A 28 × 42 ft footprint is 1,176 ft² on the ground but **1,212 ft²** of roof at 3/12. Ordering off the footprint leaves you 0.4 squares short — and that is before waste.
- The pitch factor is √(1 + (rise/12)²). There is no estimate in it and no manufacturer fudge — it is the hypotenuse. 3/12 gives 1.031.
- 10% waste for a simple gable roof: two planes, cuts only at the rakes. A simple gable wastes least because the only cuts are at the rakes; every hip and valley adds a run of angled cuts that produce offcuts nothing else uses.
- Starter and cap are separate purchases, and they are the two lines that get left off estimates. 2 bundles of starter for 140 ft of eave and rake, 3 bundles of hip and ridge for 42 ft. Using field shingles as starter voids most manufacturer wind warranties.
- At 3/12 the roof is walkable with proper footwear and a harness. Steeper than 8/12 and you are into staging.
- Tear-off is the other half of the job. A single layer of asphalt shingle weighs 200–350 lb per square, so this roof carries about 3,667 lb of old material to remove and skip.
Nearby sizes
- Shingles for a 26 × 42 ft roof at 3/12, simple gable
- Shingles for a 30 × 42 ft roof at 3/12, simple gable
- Shingles for a 24 × 42 ft roof at 3/12, simple gable
- Shingles for a 32 × 42 ft roof at 3/12, simple gable
- Shingles for a 28 × 40 ft roof at 3/12, simple gable
- Shingles for a 28 × 44 ft roof at 3/12, simple gable
- Shingles for a 28 × 38 ft roof at 3/12, simple gable
- Shingles for a 28 × 46 ft roof at 3/12, simple gable
- Shingles for a 28 × 42 ft roof at 4/12, simple gable
- Shingles for a 28 × 42 ft roof at 5/12, simple gable
- Shingles for a 28 × 42 ft roof at 3/12, hip
- Shingles for a 28 × 42 ft roof at 3/12, complex
Read more
- Repair or Replace: The Four Tests That Decide, and the One That Overrides ThemMost roofs get repaired three times before they get replaced, and the three repairs cost more than the replacement would have.
- Labor Cost to Install Shingles: Why the Same Roof Is Priced TwiceLabor is the largest line on an asphalt roof quote, and every variable that moves it is a property of your house rather than of the shingle you pick.
- Cost to Replace a Roof by Material: Price per Square Against Years of ServiceThe cheapest roof and the cheapest roof per year are rarely the same product, and which one you want depends on how long you are staying.
- Roof Replacement Cost per Square: What the Number Contains, and What Moves ItPer-square pricing is the only way to compare two roofing quotes honestly. Most homeowners are handed a lump sum instead, which hides where the money goes.