What Affects the Cost of a New Roof
Roof replacement is one of the larger projects a homeowner takes on, and the price varies more than most people expect. This page explains what a contractor is actually pricing when they measure your roof, so the number in your estimate makes sense before you see it.
Size and pitch
Roofs are measured in squares, each one a hundred square feet, and the number of squares is the starting point for everything else. Pitch matters almost as much. A steep roof slows the work down and changes how the crew has to be secured on it, so the same square footage costs more on a steep roof than a shallow one. Complexity adds to it again: valleys, dormers, skylights and chimneys all need flashing and careful detail work, and a simple rectangular roof of the same size will come in lower than one broken up by features.
The material you choose
Asphalt shingle is the most common choice and the most affordable, and within it there is a range from basic three tab up to heavier architectural shingles that last longer and carry a better warranty. Metal, tile, slate and cedar all cost more, sometimes several times more, and all last longer. The decision is rarely just price. A heavier material can require structural work to support it, and some materials suit some climates better than others, which is worth asking about rather than assuming.
Tear off or overlay
Putting a new roof over an old one is cheaper on the day and more expensive over time. An overlay hides whatever is wrong underneath, adds weight, and usually shortens the life of the new roof. A full tear off costs more because of the labour and the disposal, and it is the only way anyone can see the decking. Some roofs already carry two layers, in which case a tear off is not optional. Ask which one your estimate assumes, because two estimates can look far apart for this reason alone.
What is underneath
Nobody knows the condition of the decking until the old roof comes off. Soft or rotten sheathing has to be replaced, and that is usually priced per sheet on top of the main figure. A good estimate says what the per sheet rate is rather than leaving it open. The same goes for the underlayment, the ice and water barrier at the eaves and valleys, the drip edge and the ventilation, all of which are part of a roof doing its job and all of which can quietly be left out of a cheaper number.
Labour and access
Labour is a large share of any roofing project, and it moves with where you are. Access matters too: a roof a crew can reach easily from a driveway is quicker than one behind a fence, over a conservatory or three storeys up. Tear off also produces a lot of material that has to go somewhere, so disposal and the dumpster are a real line item. If your estimate is a single number with no breakdown, these are the parts worth asking to see separately.
Why no two estimates match
Two contractors can look at the same roof and produce very different numbers without either of them being wrong, because they may not be pricing the same work. One may assume an overlay, one a tear off. One may include new flashing and ventilation, one may reuse what is there. One may carry a workmanship warranty and the other only the manufacturer's. The useful comparison is not the total, it is the scope. Ask each estimate to say what it includes, and the gap usually explains itself.
FAQ
Common questions
How is a roof measured for an estimate?
Roofing is measured in squares, each one a hundred square feet. A contractor measures the roof surface rather than the footprint of the house, so a steeper roof contains more square footage than its floor area suggests. Pitch, valleys, dormers and chimneys all affect the labour on top of the raw measurement.
Is it cheaper to put a new roof over the old one?
On the day, yes. An overlay avoids the labour and disposal cost of removing the old roof. Over time it is usually more expensive, because it adds weight, traps heat, hides any problem with the decking underneath and tends to shorten the life of the new roof. Some roofs already carry two layers and cannot take another.
What is decking and why does it affect the price?
The decking is the wooden sheathing the roof covering is fixed to. Its condition cannot be seen until the old roof is removed, so damaged sheets are usually priced separately and added to the final figure. An estimate that states the per sheet rate in advance tells you what a surprise will cost before it happens.
Why is one estimate so much lower than another?
Usually because the two are not pricing the same work. One may assume an overlay rather than a tear off, reuse existing flashing and ventilation, use a lighter shingle, or carry no warranty on the installation itself. Comparing the scope rather than the total normally explains the difference.
Does a more expensive roof last longer?
Often, though not always in proportion. Heavier architectural shingles generally outlast basic three tab, and metal, tile and slate generally outlast asphalt. Installation quality and ventilation affect how long any roof lasts, which is why the contractor matters as much as the material.
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