When purchasing a new roof, one of the first questions that homeowners usually have is how much the roof is going to cost. There are several factors that help determine the final cost of a new roof, including the roof’s size. Roof surfaces are measured in a unit called a square. A square, as it pertains to roofing, is equal to 100ft2 of roofing space that needs to be covered. A square commonly contains three bundles of shingles, but depending on the size and weight of the shingles, it’s not uncommon for a square to require four or even five bundles per square. Depending on the shingles that are chosen for the project, a square of asphalt shingles can vary from $150-700+ per square. Premium material, such as concrete tile, wood or solar, will cost significantly more per square.
Determining how many squares make up a roof requires the roofer to take length and width measurements of the roof’s surface, including all overhangs and oddly-shaped spots (such as a dormer) to find its square footage, then divide the total square footage by 100.
For example, let’s say the total square footage to be re-roofed is 2400ft2. The roofer will divide this number by 100 to arrive at the final number of squares needed to re-roof the home.
2400 / 100 = 24 squares
These measurements should be done by experienced roofers, as the different parts of the roof, such as the pitch and dormers, as well as a correction factor, will need to be carefully measured and taken into consideration.
It’s important to note that 10-15% may be added to the final material measurement as trim allowance (waste factor). The actual amount of waste will be evident once the roof is completed, and if there are leftover shingles, they can be kept to replace any areas of damage in the future. Roofs with more complicated layouts tend to have a higher waste factor than plain gable roofs due to the increased number of unique cuts to accommodate corners, walls and edges.
Most roofing projects require equal amounts of underlayment and shingles. So, a 2400ft2 roof would require 24 squares of underlayment.
Like shingles, underlayment comes in various options as far as weight, composition and quality. Synthetic underlayment typically comes in rolls that cover 10 squares each, while a roll of regular #15 felt underlayment is often able to cover just four squares.
So, the 2400ft2 roof would require 2.4 rolls of synthetic underlayment or six rolls of #15 felt.
Synthetic: 24 squares / 10 squares per roll = 2.4 rolls
#15 Felt: 24 squares / 4 squares per roll = 6 rolls
Remember to add 10-15% for trim.
Nails Generally speaking, each shingle should be secured with four nails (five per shingle for the starter course). For a typical 3-tab shingle roof, this equates to 320 nails per square, but for high-wind areas, this number could be up to 30% higher. Of course, other styles of shingle can require fewer (or more) nails per shingle, and the number of shingles per square can vary depending on the type of shingle being used.
Sheathing When the old roof comes off, a roofer will be able to see the state of the home’s deck sheathing. Sheathing is the plywood to which the roofing material is attached. Each sheet of plywood measures 4’ x 8’ and can vary in thickness from ¼” to ⅝”. Given these measurements, a square requires roughly three sheets of plywood sheathing.
Replacing any rotten sheathing is required by state building codes, so if the old sheathing is damaged, rotted or otherwise unsuitable to meet the standards of the state or county inspector, the price of the finished roof could be far more costly than originally planned. Of course, only the damaged boards need to be replaced, typically at $70-100 per sheet, depending on the roofing company’s labor cost and the current price of lumber.
Flashing & drip edge Flashing is a metal or vinyl strip attached to the roof to block water from entering through roof penetrations, such as skylights, chimneys and roof vents. As one of the most vulnerable components of a roof, the flashing is typically always replaced during re-roofing. The cost to replace flashing is typically around $15-25 per linear foot, including the caulking needed to seal it.
The drip edge is the overhanging area of the roof; it extends beyond the fascia to help direct water to the gutters as well as keep pests out. This is also a crucial component of the roof, as a missing or damaged drip edge can lead to rotted deck sheathing.
Waterproof barrier This barrier, which is adhered to the roof, provides another layer of protection against invading moisture and is a code requirement. A double layer of water barrier is recommended, as keeping the water out helps protect the home from mold, leaks and other moisture-related problems.
Ventilation Every roof needs proper ventilation to preclude mold growth and wood rot. It’s crucial that the roofer does not skip replacing attic fans or other ventilation components as needed when completing a roofing job.
Tear-off In Florida, it is required by law that the old roof is completely torn off before installing new roofing materials. The labor to do so, as well as the debris haul-away, will contribute to the final price.
The final price per square depends on the materials used and the roofer’s cost for labor. It’s always a good idea to ask the roofer what is included in the final estimate, but typically, the estimate will include all labor and materials. A roofing calculator can provide a rough estimate on a new roofing system. To schedule a free in-person roof inspection and estimate, call AKVM today at 941-727-3996.
AKVM is a Florida state-certified roofing contractor. For nearly 20 years, we’ve been helping homeowners in Sarasota and Bradenton build durable roofs.. If you’re looking to upgrade your roof and need expert advice, we invite you to contact us right away.
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