Asphalt shingle re-roof cost: a full worked example with tax and holdback

This worked example rebuilds a complete asphalt shingle re-roof quote for a typical two-storey Canadian house, from measurement to the final payment. With about 16.5 squares, two layers torn off, eight sheets of new decking, new ventilation and flashing, the illustrative contract comes to $15,620 before tax: $17,650.60 with Ontario HST, or $17,959.10 with GST and QST in Quebec. In Ontario, the owner would keep back 10% of the value of the work as a lien act holdback and release it once the lien period has passed with no lien registered. Change the numbers to match your own quotes; the method stays the same.

This guide is part of how to compare roofing quotes. Every price is illustrative and chosen to make the arithmetic clear, not a market rate.

The house

Two-storey detached house, footprint 34 × 28 ft with 1 ft overhangs → 36 × 30 = 1,080 sq ft.
Simple hip roof, 7/12 pitch, plus a small 4/12 porch roof of 8 × 20 ft footprint (160 sq ft).
Two existing layers of shingles, some soft spots near the eaves.
One brick chimney, two plumbing stacks, one bathroom fan vent.

Step 1: measure

Section	Calculation	Sloped area
Main roof	1,080 × 1.158	1,250.6 sq ft
Porch roof	160 × 1.054	168.6 sq ft
Subtotal		1,419.2 sq ft
With 14% waste (hip roof)	1,419.2 × 1.14	1,617.9 sq ft

Rounded: about 16.2 squares. In this example the contractor's measurement says 16.5 squares for field shingles, which agrees closely with ours; the small difference is rounding up to whole bundles. A quote saying 22 squares for the same house would deserve a question. See how to measure your roof in squares.

Step 2: price the lines

Line	Calculation (illustrative)	Amount
Tear-off, first layer	16.5 squares × $70	$1,155
Tear-off, second layer	16.5 squares × $45	$742.50
Architectural shingles installed, incl. synthetic underlayment	16.5 squares × $520	$8,580
Ice and water membrane at eaves and valleys	lump sum	$950
Drip edge, eaves and rakes	190 linear ft × $4	$760
Starter strip and hip/ridge cap	lump sum	$640
Chimney re-flashing with counter flashing	1 × $650	$650
Plumbing stack boots and fan vent	3 × $60	$180
Ridge vent	30 linear ft × $12	$360
Replacement decking (allowance)	8 sheets × $95	$760
Disposal bins (two layers)	2 × $420	$840
Subtotal		$15,617.50

The contractor rounds to $15,620 on the contract. Note how the unit price for decking keeps the final cost predictable: if 12 sheets are needed instead of 8, the price rises by 4 × $95 = $380, not by an unknown amount.

Step 3: add sales tax

Province	Tax calculation	Total
Ontario (13% HST)	$15,620 × 0.13 = $2,030.60	$17,650.60
Quebec (5% GST + 9.975% QST)	$781 + $1,558.10 = $2,339.10	$17,959.10
Nova Scotia (14% HST)	$2,186.80	$17,806.80
Alberta (5% GST)	$781	$16,401

Quebec QST: $15,620 × 0.09975 = $1,558.095, rounded to $1,558.10. See GST/HST, PST and QST on roofing.

Step 4: payment schedule with holdback (Ontario example)

Ontario's Construction Act requires an owner to keep back 10% of the price of services and materials supplied under a contract, until the lien period has expired. A sensible schedule for this job:

Stage	Amount
Deposit on signing (to order materials), with tax	$2,000
On substantial completion: value of work $15,620 + HST = $17,650.60, minus 10% holdback ($1,765.06), minus deposit	$13,885.54
Holdback, released after the lien period expires with no lien registered	$1,765.06
Total	$17,650.60

Arithmetic: $17,650.60 − $1,765.06 − $2,000 = $13,885.54. This example applies the holdback to the tax-inclusive amount for simplicity; the contract should say how tax on the holdback is handled. The holdback calculator does this arithmetic, and the holdback guide explains when to release it.

In Quebec there is no statutory holdback, but the contract can provide for a retention, and owners can protect themselves against legal hypothecs from subcontractors and suppliers; see the holdback guide for details.

Step 5: what could change the total

Change	Effect (illustrative)
12 sheets of decking instead of 8	+$380
Upgrade to impact-resistant shingles at +$150 per square	+$2,475
Steel shingles at $1,100 per square instead of $520	+$9,570
A third hidden layer	+$742.50 tear-off and possibly one more bin
Rebuilding the chimney crown	priced separately by a mason

Steel example: 16.5 × ($1,100 − $520) = 16.5 × $580 = $9,570.

Step 6: compare with the estimator

Enter 1,650 sq ft (16.5 squares) in the roof replacement cost estimator with the architectural asphalt preset of $4.50–$7.50 and about $4,150 of extras (both tear-offs $1,897.50, bins $840, decking $760, chimney $650): low = 1,650 × $4.50 + $4,150 = $11,575; high = 1,650 × $7.50 + $4,150 = $16,525. The $15,620 contract sits in the upper part of that illustrative range, which is a prompt to ask the contractor what justifies it, not proof that it is wrong.

Lessons from the example

Measure first; it is the multiplier for everything.
Insist on unit prices for unknowns such as decking and extra layers.
Get flashing and ventilation written as separate lines.
Keep the deposit modest and the holdback in place.
Add tax before you compare totals with your budget.

FAQ

Why does the second tear-off layer cost less?

In this example the crew is already stripping the roof, so the extra layer adds labour and disposal but not setup. Contractors price it differently; some charge the same for each layer.

Should the contractor charge for the bins?

Disposal is a real cost, whether shown as a line or included in the per-square price. Ask so you can compare like with like.

Is a deposit of 10–15% normal?

It is common to pay a deposit to cover materials. Contract rules in some provinces limit or regulate deposits for certain contracts; see what a roofing contract should include.

Sources

Canada Revenue Agency — GST/HST rates
Revenu Québec — QST
Ontario e-Laws — Construction Act holdback and lien rules
National Research Council Canada — National Building Code of Canada