How Much Does It Cost to Install a Flat Roof?

In this guide

Flat Roof Cost per Square Foot

The average cost of installing a flat roof ranges from $4 to $30 per square foot installed. The total cost of the project differs depending on the size of your roof and the type of material you choose. You can expect to pay more for a larger roof than a smaller roof. You can also expect to pay more for a high flat roof with many obstacles than an easily accessible flat roof with very few obstacles.

Flat Roof Material Prices

The cost of a flat roof is influenced by the material selected, ranging between $4 to $30 per sq.ft. installed. Many materials are available to choose from that differ in their pros, cons, lifespan, and cost and are known for their installation process, structural integrity, and ability to withstand harsh weather. You can expect to pay more for an EDPM roof compared to a GRP roof. The table below lists the most popular types of materials available and their respective costs, followed by an explanation of each.

GRP Flat Roof Cost

GRP roofs are $4 to $6 per sq.ft. GRP, also referred to as glass-reinforced plastic, is crafted from a polyester resin made to form a laminate. GRP is a very popular choice of flat roofing material not only because of its durability but also because of its lightweight. The advantages of GRP roofs include flexibility and easy repairs. A few disadvantages of GRP roofs are that they are not for larger roofs, and the weather plays a factor in the installation process. Fiberglass roof installations require lots of preparation and experience. Installation involves removing the existing roof, laying plywood, and installing fiberglass roof drip trims. Then, waterproof matting is applied to the seams. Finally, the GRP is laid out and followed by the application of the topcoat. You can expect this material to last for up to 25 to 50 years.

Single Ply Membrane Flat Roof

A single-ply membrane roof is generally the most popular. They can be made of PVC, other plastic, or rubber, such as ethylene propylene diene terpolymer (EPDM), and are quick and easy to install. They are heated and stretched across your roof and adhered using either a solvent adhesive or modified bitumen or torched to the roof. Some types may even use metal anchors. They can last up to 40 years and, typically, hold up better to rainfall and other elements. Some advantages of single-ply membrane flat roofs include easy installation, lower maintenance and repair costs, and a longer lifespan. Also, a removed single-ply roof can be recycled. Disadvantages include the membrane can be easily punctured due to its lightweight material, UV rays can deteriorate the adhesive over time, and the seams are vulnerable to leaks. A single-ply membrane roof costs between $4 to $7 per sq.ft.

Polyurethane Flat Roof

Polyurethane, most commonly referred to as SPF, is a cold-applied liquid material either sprayed or rolled onto a flat roof that expands into foam. It creates a white layer across the roof and provides a waterproof membrane for roofing systems. This type of roofing has been around for many years. Advantages of polyurethane roofing include easy installation, energy efficiency, easy maintenance, and that it is waterproof. Some disadvantages are accurate repairs are needed, overspray potential, and a limited installation window. If properly maintained, your SPF roof can last over 50 years. You can expect to pay between $4 and $7 per square foot.

Flat Concrete Roof Cost

Flat concrete roofs average in cost between $4 to $8 per square foot. If you are looking for a roofing material that you can rely on for many years, concrete is one of the best options. Flat concrete roofs have many pros, including hassle-free maintenance, high durability, and the ability to withstand harsh weather conditions. With the pros come a few cons, including leakage problems and plant growth. This type of roofing material can last for over 50 years. Concrete is generally low maintenance and very durable.

Modified Bitumen Flat Roof

A modified bitumen roof is made up of sheets that are composed of multiple layers, including bitumen or tar. They are generally heated with a blow torch when rolled out onto the roof, adhering them in one step. You will have more seams with this style of roof. However, they are fairly easy to install and durable once finished. They only last 10 to 15 years, so they are less common. This flat roofing material is known for its light hue that reflects heat. They cost between $4 and $8 per sq.ft.

Fiberglass Flat Roof Cost

A fiberglass flat roof averages between $4 and $8 to install. Fiberglass is a newer roofing material that works well for both pitched and non-pitched roofs. It is installed using panels that are installed on the roof overlapping each other. Most times, fiberglass roofs are double layered. This type of roof is popular due to its cost and water-resistant properties. A fiberglass roof is much more durable than other materials and lasts for 25 plus years. A few disadvantages include the installation is based on the weather, and they aren’t recommended for larger roofs.

Built-Up Flat Roof

Built-up roofs are some of the first types of flat roofs and pre-date modified bitumen roofs designed to replace BURs. This roofing stacks multiple layers of membrane with bitumen between them, with a final reflective coating. They may be covered in rocks or crushed stone and are mostly seen on commercial buildings with very few residential settings. BUR is mostly recommended for this style of roof because it creates a continuous sealed surface and provides greater longevity. Expect to pay another $2 a sq.ft. for added layers. They last 10 to 12 years and are time-consuming to install. They cost around $4 to $10 per square foot.

Metal Flat Roof Cost

Metal roofs are much less common than they once were. Their prices range from $4 to $30 per sq.ft. Corrugated tin roofs were sometimes used on flat buildings because they were very durable and long-lasting. They can be very noisy and tend to rust. The installation process is quite easy, with the metal sheets fastened to the deck. Metal roofs last decades when well-maintained and reduce cooling costs by as much as 25% in the summer months. A few disadvantages include expansion, inconsistency in color match, and the need for regular painting. Zinc roofing is a popular choice of this style of metal roofs due to its long lifespan of 60 to 100 years or more in the right climates. Zinc has a naturally occurring, self-healing property that allows the roof to reseal itself after any surface penetrations. This self-healing ability eliminates the need for maintenance.

EPDM Flat Roof Cost

EPDM roofing costs between $4.50 to $10.50 to install. EPDM, which stands for ethylene propylene diene terpolymer, is an extremely durable rubber roofing material widely used worldwide in low-slope buildings. EPDM is installed over a felt-covered insulation board using screws and metal fasteners to secure the board to the deck. This type of roofing material is very lightweight, resists sun damage, and can last up to 50 or more years with proper maintenance. A few disadvantages may be noted, including that the roof is easy to damage and susceptible to shrinkage. Also, they are not aesthetically pleasing. EPDM is available in two colors, including black and white.

Flat Roof Installation Cost by Type

The type of flat roof affects the overall project cost the most. Tile prices vary between $4 and $35 per sq.ft, installed. Every type is made of a different material with its own advantages and disadvantages. Make sure you analyze what you need to pick the best type for your home. The chart below highlights the different types of types of roofs that are flat and their respective costs, followed by subsections giving a brief explanation of each type.

​Cold Flat Roof

A cold flat roof design places the insulation between or under the timber rafters, even with the ceiling joist. This construction leaves the roof and timbers cold, which requires a breathable membrane between the roof and insulation. Cold roofs are a great option due to their cost-effectiveness, low impact, and ease of installation. A few disadvantages are cold roofs can be tricky to install on existing roofs. Also, the design requires adequate ventilation to prevent dampness between the insulation and the structure. The average cost for this type of roof ranges between $4 and $9 per sq.ft.

Inverted Flat Roof

Inverted roofs are a type of roof where the waterproofing layer lies beneath the insulation rather than above it like it is in other forms of roofing. This type of roof ensures that the roof is kept warm during the winter months and a moderate temperature during the warmer months. Inverted roofs provide excellent thermal performance, resist water absorption, are unaffected by freezing, and are protected from UV damage. A few disadvantages to these types of roofs are that they must bear the dead load of the system. Also, it can be very difficult and expensive to locate leaks. The average cost of an inverted roof ranges between $4 and $9 per sq.ft.

Hybrid Flat Roof

A hybrid flat roof, sometimes referred to as a compact roof, combines elements of warm and cold roof construction. Most of the insulation in a hybrid type of roof is put between the rafters under the roof deck. A few main advantages of hybrid roofs include maximum thermal performance and minimizing the thickness of the roof. The main disadvantage of a hybrid roof is that it can be more difficult to install than others. You can expect to pay between $4 and $11 per sq.ft. for a hybrid type of roof.

Warm Flat Roof

A warm flat roof is a roof in which the insulating layer is located above the joists and deck. This design allows for a similar temperature in the roof and loft as in the interior of the building. Warm roofs make the entire building warm to avoid any heat or energy loss. There are many advantages in installing a warm roof, including their simplicity, effectiveness and easiness of insulation, eliminate cold bridging, allow moisture to escape, thermal efficiency, and cost-effectiveness. A few disadvantages are that they can be more difficult to install than a cold roof, and scaffolding may be required. The average cost for this type of roof ranges between $6 to $11 per sq.ft.

Tapered Flat Roof

A tapered roof system is where the slope or “pitch” of the roof is formed by the insulation itself. While still having the benefits of a flat roof, the slope drains excess water and debris. More effective drainage extends the lifespan of your roof and makes it easier to maintain. Tapered roofs have many advantages, including lightweight material, increased drainage abilities, and quick installation. You can expect to pay between $7 and $10 per sq.ft. for a tapered roof.

Curved Flat Roof

A curved flat roof is a roof that has a curved style. A curved roof consists of a single gable with one side with a very little slope and the other side sloped down. These types of roofs give more attraction and charm to the building. The purpose of these roofs is to shed the snow and rainwater. They are advantageous because they require less framework, reduce the emission of CO2 gases, and do not require skilled supervision. On the downside, curved roofs are more expensive because of their complex design. You can expect to pay between $8 to $15 per sq.ft.

Flat Green Roof

Green roofs are a great way to insulate your home or building and help manage stormwater runoff. They come in three different types and can be constructed of plants placed directly on the roof or made of modular planters. Green roofs have many advantages, including thermal performance, increased lifespan, and an improved drainage system. A few disadvantages include their heavyweight material and extra maintenance. Green roofs can be very expensive, so expect costs to start at $10 and go as high as $35 per sq.ft.

Cost to Install Flat Roof

For the installation of 1,500 sq.ft. PVC single-ply membrane flat roof, expect to pay $3,000 to $5,000 in labor and $4,000 to $5,500 in materials, for a total average cost of $7,000 to $10,500. The material costs $2.50 to $3.50 per sq.ft. Labor costs between $1.50 and $3.50 per sq.ft. The total cost of the labor is generally based on the material. Single-ply membranes are the least expensive to install, while a built-up roof can be labor-intensive. Other issues that may impact the cost of the labor can be the condition of the roof, whether you have any cuts in the roof for lights or a chimney, and whether the roof needs to be reinforced to hold things like an air conditioner unit. In these instances, labor may climb as high as $10 to $15 per sq.ft.

The installation process for a flat roof varies depending on the type of roof installed. Single-ply membrane roofs, no matter what they are made of, are generally heated, stretched, and adhered directly to the roof in a single layer. This is the fastest and easiest method of installing this style of roofing. Modified bitumen roofs will be rolled out and torched or heated with a blow torch as they are rolled onto the roof, sealing them in place. The edges are usually overlapped and heated together to help form a tight seam. Built-up roofs have multiple layers laid, then coated in bitumen, with each one being placed on top of the next. They are generally sealed and topped with stone as the last layer. Metal roofs are installed similarly to other metal roofs, with the panels laid out and interlocked at the seams.

Flat Roof Replacement Cost

The process of flat roof replacement involves tearing off the existing roof and replacing it with a brand new roof. The average cost for roof replacement is around $7,000 to $12,000. A new installation involves installing a new roof and tearing off any existing roofing, which costs between $7,000 and $10,500. While replacing your entire roof can be quite pricey, there are many benefits to consider, including correcting any issues at one time. Repairing certain areas may cause other areas to require repair in the future, so replacement may help save money in the long term. Roof replacement improves the curb appeal of a home and can be a good investment for selling.

Flat Roof Extension Cost

The price you will pay for a roof extension varies depending on the size. Flat roof pricing ranges from $1,000 to $20,000. A roof extension can be done for various reasons, such as adding a kitchen, bedroom, office, or updating your home. The advantages of building a roof extension outweigh the cons. Building this type of roof is an affordable way of extending your living space and increasing your home's curb appeal. There aren’t many disadvantages to extending your roof other than your ceilings are lower than a pitched roof extension.

Flat Roof Insulation Cost

Insulating a flat roof averages $500 to $2,500, depending on the roof size. Larger roofs require more insulation. Because this style of roof usually has little to no pitch, they must be insulated against moisture. Some types of flat surface roofing material, like metal, also require insulation to help deaden the sound. Many homeowners prefer to use a type of insulation to improve energy usage on the roof. Generally, a rigid insulation board should be used as part of the roofing construction and may be applied over or under the roofing deck. Either extruded polystyrene (XPS) or insulated panel system (IPS) insulation can be used, provided that the insulation is breathable and developed for moisture management.

Flat Roof Vent

Flat roofs need ventilation, like a pitched roof. These vents costs between $300 and $550. Most vents used on rooofs that are flat are similar to those used on pitched roofs. However, some are recommended over others. Some common vent types for flat roofs include box roof vent, boot vent, breather vent, mushroom vent, or a pop vent. Flat roofs have a unique design that makes them great for many roofing situations, except in climates with large quantities of rain and moisture. Due to their flat design, they require drainage systems that remove rainwater and moisture from the foundation.

Flat Roof Underlayment

Roofs need an underlayment or membrane to protect the deck. Underlayment is a waterproof seal placed underneath the roofing tiles to seal and protect it from harsh weather. A sturdy underlayment is extremely important in roofing to protect your roof and prevent leakage. Underlayment is even more important in flat roofs as the water does not run off the flat surface as easily as it does on a pitched style of roof. The most popular type of underlayment in flat roofing is synthetic underlayment. The cost of synthetic roof underlayment ranges between $0.75 and $0.90 per sq.ft.

Flat Roof vs Pitched Roof Cost

Flat roofs are less expensive than pitched ones, averaging between $7,000 and $10,500 for a flat roof and $7,000 and $12,000 for a pitched roof. While the initial cost may be cheaper, it is important to keep in mind that they will often require more maintenance which could cost more in the long run. Flat roofs don’t drain well, leading to leaking, clogging, and repairs in the future. Pitched roofs last longer and require less maintenance over time. Ultimately, the decision between pitched or flat roofing comes down to personal preference.

Pros and Cons of a Flat Roof

Flat roofing is less common than other types of roofs, mostly due to their disadvantages. Firstly, they do not allow rain or snow to run off easily, so they tend to stay wetter than other roofs. They may hold more snow for longer and are difficult to clear. This means that they require more maintenance than roofs with a higher slope. However, a flat roofing is often less expensive to build and finish. And, it gives contemporary homes a sleek appearance. In some instances, a non-pitched roofs can be used as a garden or recreational area for the residents. It is also possible to plant on a flat surfaced roof, creating a green roof system.

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Flat Roof Maintenance

Flat roofs generally require more maintenance than a sloped or pitched roof. This includes annual inspections to look for issues, such as cracks or breaks, and keeping the roof clean and free of debris. If you notice leaks, address these quickly by sealing the roof to prevent the problem from spreading. If you have overhanging trees, have those trimmed back. In snowy climates, ensure that you have the roof shoveled regularly to prevent the weight from becoming too much for the roof structure.

Enhancement and Improvement Costs

Seal Flat Roof

Sealing a flat roof is an enhancement to your roof. It provides additional protection to prevent leaks from occurring and extends the roof’s lifespan. If you choose to apply a sealant, your roofing contractor will use an acrylic adhesive to seal the roof at the time of installation. Different sealants may be needed, depending on the type of roofing material. You can expect to pay from $50 to $500, depending on the type and application.

Flat Roof Flashing

If you have chimneys, skylights, vents, curbs, or other penetrations in the roof, you need to line them with flashing. Flashing is a thin metal material used to seal the edges of the roof and prevent water damage. It is usually made from steel, copper, or aluminum and resists water and weather. However, it naturally wears down over time or may become damaged due to impacts in storms. Flashing installation costs between $500 and $1,000, depending on the type and placement.