What Is a Roofing Square, and How Many Do I Need?

Squares, bundles and why both exist

The square is the unit the trade quotes in — labour, tear-off, disposal and material all come priced per square. The bundle is the unit you can actually carry: three bundles of standard architectural shingles cover one square, and each weighs enough that three is a sensible package for one person on a ladder. Heavier designer shingles run four or five bundles to the square, so check the wrapper rather than assuming three.

Everything else on the roof follows the same unit. Underlayment comes in rolls covering a set number of squares, and starter strip, ridge cap, drip edge and valley flashing are priced per linear foot of the edges rather than per square, which is why a cut-up roof with many hips and valleys costs more per square than a plain gable.

The pitch multiplier

Roof area equals the footprint area times a multiplier set by the pitch. A 4/12 roof multiplies by 1.054, a 6/12 by 1.118, an 8/12 by 1.202 and a 12/12 by 1.414. Those are the diagonal of the rise-and-run triangle, and they apply to the plan area covered by the roof — which includes the overhangs, not just the heated floor.

Take a 2,000 square foot single-storey house with a 6/12 roof and 2 foot overhangs. The covered plan area is nearer 2,300 square feet, and the multiplier takes the roof to roughly 2,570 square feet — about 26 squares before waste, not the 20 the house size suggests. A two-storey house of the same total floor area has half the footprint and therefore roughly half the roof, which is why square footage alone tells you very little.

Waste, and what else goes on the order

Add 10 percent for a simple gable roof and 15 for a roof with hips, valleys, dormers or many penetrations, because every hip and valley cuts shingles at an angle and the offcuts are unusable. Then round up to whole bundles.

The material list is longer than shingles. Underlayment over the whole deck, ice and water shield at eaves and in valleys where the code requires it, starter course along every eave and rake, ridge cap along every ridge and hip, drip edge on all edges, and enough nails — roughly four per shingle, more in high wind zones. Add plywood for the deck sheathing you will find rotten once the old roof is off, because on a re-roof you almost always find some.

Tear-off and disposal

Removal is priced per square and per layer, and it is not a small part of the total. A square of old asphalt shingles weighs 200 to 350 pounds depending on type and how many layers are on there, so a 26 square roof with two layers is around 10 to 15 tons of waste — a dumpster question rather than a truck question.

Check how many layers exist before pricing anything. Many jurisdictions allow at most two layers, so a second layer means the whole roof must come off rather than being covered over, and that changes both the labour and the disposal lines materially.

Common questions

How many square feet is a roofing square?

Exactly 100 square feet of roof surface. It is a unit of roof area, not of house floor area.

How many bundles of shingles per square?

Three for standard three-tab and architectural shingles. Heavier designer profiles run four or five bundles per square — check the wrapper.

How many squares is a 2,000 sq ft house?

For a single storey with a 6/12 pitch and normal overhangs, roughly 26 squares before waste. A two-storey house of the same floor area has about half the roof.

How much waste should I add?

10 percent on a simple gable, 15 percent on a roof with hips, valleys or dormers, then round up to whole bundles.

In this topic

• Roof Replacement Cost Calculators
• Guides