What Determines Roof Replacement Cost?

If you are in the market to replace the roof on your home, you probably have a lot of questions. One of the primary concerns, inevitably, is how much this is going to cost. Homeowners are often unaware of what exactly goes into the process of replacing a roof and what goes into calculating the cost of each project. Before getting an estimate, you may want to find out what factors are considered by contractors when offering a price. This way you will be better informed and able to evaluate the fairness of any given price. Remember, you should always contact reputable and licensed roofing contractors and compare their estimates before agreeing to any contract.

To help you understand how contractors arrive at the number you may see on an estimate, below we detail the factors involved in our calculations of roof replacement.

Size of the Roof

The most obvious factor to consider is the size of the roof. You may think that you can get an estimate of your roof’s size based on the square footage of the house, and you are right, but with several caveats. Firstly, the square footage listed on most documents related to the property, and the one used by realtors in making a sale, is the square footage of the living area. This often excludes areas that are under the roof, but are not considered lived-in because they are not connected to the HVAC system of the house. This may include the garage, attic spaces, and screened or unscreened porches. Likewise, for a two story or taller structure the square footage will include all the floors, but the roof often covers only one total floor (although this may differ based on the architecture of the house).

Another element to consider in roof size is the pitch of the roof. Unlike the square footage of the house itself, the square footage of the roof also depends on its slope. The steeper the roof, the greater the difference between the house size and roof size. Roof slope is typically expressed in rise over run. That is, how many inches the roof rises over a 12 inch horizontal run. A 4/12 roof is fairly low sloped, while a 10/12 is very steep. Roofing contractors typically use roofing calculator tables or take hands-on measurements to make these calculations. The final roof size measurement is then expressed in roofing squares. Each roofing square is 100 square feet. For instance, a roof of 2500 square feet would be measured as 25 squares. Once the contractor has this square measurement, they use a per-square rate as a multiplier to calculate the total price. This multiplier includes material, labor, and overhead costs and varies based on the factors below.

Materials

The primary factor that affects price is material type. As we have discussed before, tile is more expensive than metal, which in turn is more expensive than shingles. Even in choosing a particular type of tile or metal or shingles there may be price differences. For instance, a higher quality shingle with greater wind resistance may be more expensive than a lower quality type. You should decide which material you want to use for your roof replacement ahead of time, so that any contractor you call can give you an appropriate estimate for that material.

Underlayment, the layer between the decking and the roof covering, also affects cost. Synthetic underlayment is cheaper than peel and seal (ice/water barrier membrane), but the latter is better at waterproofing. An estimate should always specify which underlayment the contractor is offering and may give two different prices (one for synthetic and one for peel and seal) and leave the choice up to the homeowner.

There are also additional materials that go into roof replacement, like metal vents, drip edge, flashing, and nails. These are all included in material costs. Material costs constantly change based on market price, so any estimate will have an expiration date after which the contractor cannot guarantee the given price. This is typically expressed as a period (say 15 days) after the date of the estimate. 

Decking

During roof replacement, it is typically necessary to replace some amount of damaged wood decking (plywood or OSB depending on the construction of the house). Because it is impossible to see how much decking needs replacing until the old roof is torn off, contractors include a small amount of decking in the initial estimate and reserve the right to add any additional wood replacement to the final invoice. This should be explicitly stated in any contract you sign for roof replacement.

Slope and Shape

The per square multiplier for the roof price also changes based on slope and shape of the roof. A steeper roof is not only larger, but also a more hazardous working environment. For this reason, steeper roofs will have a steeper price since they require special equipment and higher labor costs.

The roof’s shape and how many sub-roofs it has will also alter price. The more “cut-up”  a roof is (the more its shape deviates from a simple single gable design), the higher the price. This is due to the difficulties and the extra material involved with accommodating unusual shapes, which can require specialized labor and a higher waste factor in cutting up material to fit the shape. 

Dumping Fees

A roof replacement estimate will also typically involve dumping fees. This is because the materials torn off of the old roof must be disposed of properly. This requires a trailer (rented or owned by the contractor). The trailer must also be emptied at the local municipal waste facility which typically charges for dumping a rate based on the weight of the materials dumped.

So, as you see, there are a multitude of factors that go into estimating roof replacement. If you are interested in roof replacement and you are in the Palm Coast, Flagler, or Volusia area, please give Florida’s Best Roofing a call at 386-263-7906 for a free estimate! We will be happy to answer any questions you have about your estimated price.