How Much Does a Flat Roof Replacement Cost?

Reviewed by Carol J Alexander remodeling expert. Written by Fixr.com.

If you’re spending too much time emptying buckets of rainwater from your mid-century modern dining room, it’s time to replace the roof. Hopefully, it hasn’t come to that. But it’s never too soon to prepare, especially if you see protrusions or loose seams. 

Unlike the ubiquitous pitched roof you see on most homes, a flat roof has a slope of only ¼-inch per 12 inches of horizontal length. Therefore, it calls for different types of materials and methods in roofing. The average cost of replacing a flat roof in the U.S. ranges from a budget-friendly $1,150 to $52,275 on the high-end.  

Flat Roof Replacement Costs

Factors that influence the cost of flat roof replacement

The options in flat roofing materials are less varied than those for a pitched roof. But still, the roofing materials, the roof size, and where you live affect the project's total cost. So, to help you plan for your new flat roof replacement, let’s look at all the circumstances that will impact your budget.

Geographic location

The costs for most home improvement projects differ from one area of the country to the next. For instance, the cost to replace a flat roof on a mid-century modern home in Chicago will vary from the cost in Houston.

Some coastal regions have stringent regulations that affect cost. For instance, they require that all roofing materials be rated for high-force winds. Florida has the stiffest regulations due to the frequency of tropical storms and hurricanes in that state. Unfortunately, with those regulations come higher costs.

Labor

The cost of labor for replacing a flat roof also varies by region of the country. The national average for roofing labor is from $42.75 to $79.57 per hour.

Material type 

While not as varied as the options you’ll find for sloped roofs, there are various flat roof materials. However, some are used mainly on commercial roofs. They include single-ply roofing membranes of thermoplastic polyolefin (TPO), polyvinyl chloride (PVC), ethylene propylene diene monomer (EPDM), and rubber roofing. 

According to Pat Overson, owner of Overson Roofing in Pheonix, Arizona, other materials are rarely used in recent years and have been replaced with newer products. Those include rolled roofing. “Seams are a problem with rolled roofing,” says Overson. “It’s pretty old school.” 

For the most part, you may find the following options on flat residential roofs, depending on the area of the country in which you live.

Built-up Roof (BUR)

Also known as built-up tar, this low-cost material consists of several layers of bitumen (commonly known as asphalt). It is covered with another material to create a water-tight surface impervious to wind and weather. Gravel used to be a popular covering, but it is heavy and hides the seams, making roof leak detection difficult. So, gravel is being phased out, according to Overson. 

Instead, new BUR roofs have a mineral surface cap sheet over the asphalt. A cap sheet includes several layers of either asphalt or tar-coated fiberglass topped with mineral granules. Expect to pay from $1.35 to $3.88 per square foot of BUR roofing.

Modified Bitumen

Modified bitumen is asphalt mixed with rubber, according to Overson. Modified bitumen is heat resistant, and because it expands and contracts, the seams stay sealed. Expect to pay from $1.15 to $2.61 per square foot of modified bitumen roofing.

Self-adhering Modified Bitumen

Modified bitumen is secured to the roof deck using a torch, which makes installation hazardous on wood-framed homes. So, there is now a self-adhering modified bitumen roofing. It is sticky on one side and is safer to apply, says Overson. Expect to pay from $.65 to $1.33 per square foot of self-adhering modified bitumen roofing.

Polyurethane Spray Foam

When applied to a flat roof, polyurethane foam gives an R7 insulation rating for every inch applied. The insulation factor makes PSF a popular choice for homeowners who want to improve the energy efficiency of their homes. “The only drawback,” says Overson, “is that it’s not sunproof.” Therefore, an elastomeric coating is applied to protect the foam from UV rays. The coating lasts five to eight years and, when done as needed, gives the foam roof a 30-40 year lifespan. Expect to pay from $.63 to $4.72 per square foot for a polyurethane spray foam roof, depending on the thickness.

Metal

Two styles of metal roofing are appropriate for a flat residential roof–standing seam and screw-down panels. Expect to pay from $14.25 to $30.75 per square foot of standing seam metal roof and from $8 and $15 per square foot of screw-down insulated metal panels.

Roof size

Of course, the larger the roof, the more materials, and labor needed. On average, a typical flat roof costs from $630 to $30,750 per 1,000 square feet. If you’re unsure how large your roof is, here is a formula for you to use to calculate its size.

Square footage of the home x 1.5 = Approximate square footage of a flat roof

To make this process even easier, we’ve calculated the roof size and estimated cost to replace the flat roof for several different home sizes below.

Sealant

According to Overson, the only type of flat roof on a home that would require a sealant or coating is polyurethane spray foam. However, if you choose this type of roof for the insulation qualities, applying the elastomeric coating every five to eight years could add $0.23 to $5.60 to the overall cost, depending on the properties of the coating.

Fixing the slope

Sometimes, Overson encounters a perfectly flat roof. “That is against code,” he says. Building code requires that a flat roof slope be at least 2 percent. But if it doesn’t, the contractor must build it up to create the proper slope. This work impacts the cost of materials and labor. 

Drainage system

According to Overson, residential roofs don’t require the roof drains that commercial buildings do. Because they have at least a 2 percent slope, most water runs off. However, he says, they may install scuppers, holes through parapet walls that divert run-off to the gutters and downspouts.

The cost to replace a flat roof

Budget-friendly flat roof

The average price for a budget-friendly roof replacement is from $1,150 to $5,820.

Most homeowners experience a roof replacement at least once in their lifetime. But if your roof has taken you by surprise, you may have limited funds to replace it. You’ll find the following sizes and materials within this pricing tier.

• Small home of 1,000-1,500 square feet
• A built-up tar roof, or modified bitumen.
• No additional features like drains, HVAC, chimney, or skylights to work around.

Mid-range flat roof

The cost for a mid-range flat roof replacement is from $2,548 to $38,320, on average.

If you’ve been in your home for a while and saw a roof replacement coming, you probably have a bit of money put away for this home improvement project. In that case, you can afford a medium-priced roof. For example, this size project could include the following:

• A mid-size home of 1,500 to 2,500 square feet
• A polyurethane spray foam, self-adhering modified bitumen, or screw-down metal roof.
• May have an additional feature to work around.

High-end flat roof

The cost for a high-end flat roofing system replacement is from $37,676 to $159,079, on average.

If you live in a large home, there’s no way around spending more for a roof replacement. And some homes demand a more luxurious roof style to complement the architecture and the neighborhood. A luxury flat roof will include:

• A large home over 2,500 square feet.
• A standing seam metal roof.
• Multiple features like chimneys, skylights, and HVAC on the roof.

Common repairs to a flat roof

On average, a professional roofer charges between $342 and $3183 to repair a flat roof on a 1,500-square-foot home.

Because flat roofs have little to no slope, they can develop issues not generally found on pitched roofs. The cause of some of these issues includes items like air bubbles between the layers, UV damage, or tearing from debris. Here are the most common repairs to a flat roof you may encounter.

• Water pooling 
• Leak repair 
• Sagging 
• Hail damage

Creating a budget for your flat roof replacement

No matter what size or style of home you have, a roof replacement can be a financial burden. If your home’s roof leaks like a sieve, and you don’t have the means to fix it, there are ways to pay for your roofing project.

First, ask your roofing contractor if they offer financing. Many do, but if they don’t, visit your lender to inquire about opening a home equity line of credit (HELOC) or another home equity loan. If you’ve already spoken with a roofing contractor, you should have a cost estimate to share so the lender can qualify you for the loan. 

Ways to save money on a flat roof replacement

There are many ways to cover your mid-century modern style and stick to a budget. Here are a few money-saving tips to help you save on your new flat roof.

• While flat roofs generally are a pro-only job, a skilled homeowner should have no trouble using self-adhering modified bitumen, according to Overson. “It’s peel and stick,” he says, “like a really wide Band-Aid.”
• Ask them if the old roof can be covered over. If so, you save on the demolition costs.
• If the roofing contractor says the roof deck needs replacing, ask them to show you why. If it looks sound to you, ask about other options.
• Schedule the work before it’s an emergency. Every region has a slow season. Taking advantage of it could mean savings in your pocket.
• If your roof suffered storm damage, contact your insurance agent to see if repairs or replacement are covered.

Other considerations

A few additional items to consider before replacing your flat roof include

• Building permits — Depending on your roofing contractor, you may not even realize this expense is built into the cost of the job. But DIYers need to consult with local authorities for requirements regarding permits, inspections, and fees, which vary by location.
• Timeline – Roof replacements require two to three days of fair weather. So, most roofers will want to work in the warmer seasons.
• Hidden damage — Unfortunately, you could remove the old roofing material to find damage to various roof components. When your roof leaks, the roof deck, soffit, or fascia could exhibit water damage that leads to mold or rot. The cost of repairs will add to your total budget.
• HOA – Some homeowners’ associations have strict guidelines regarding what you use on the exterior of your home. So, it may dictate what materials and colors you can use on your roof. Always consult with your HOA before committing to your roof replacement.
• Warranties – Ask your roofing contractor about warranties on materials and workmanship.

Don’t put it off

Replacing a flat roof is a big job. But since a roof protects the entire home, it’s got to be done asap. And you won’t regret it. The National Association of REALTORS 2022 Remodeling Impact Report suggests homeowners recoup a 100 percent return on investment when they replace their roofs. Installing a flat roof requires a different skill set than a pitched roof with asphalt shingles, so many roofing companies don’t install them. To ensure you’re covered, find a local roofing contractor specializing in flat roofs.