7 Types of Flat Roof Systems - New England Metal Roofing (2023)

With a flat roof, you have usable space on your house for large air conditioning systems, solar panels or, in the case of many apartments and company buildings, a garden terrace. But flat roofs also bring unique challenges and different styles. So what types of flat roofs are there and which one is the best?

Table of contents

  • What is a flat roof?
    • Pooling Water Issues
  • Built-up Canopy (BUR)
  • Modified bitumen roofing
  • Single layer membrane (EDPM, PVC, TPO)
    • PVC - Polyvinylchlorid
    • TPO – Thermoplastisches Polyolefin
    • EPDM - Cured Ethylene Propylene Diene Monomer
  • SPF - Polyurethane Foam Spray
  • BUR vs. MB vs. Single-Ply vs. SPF

What is a flat roof?

Roofs come in two classifications - low pitched or steep pitched. Flat roofs are considered flat if the pitch is less than 3:12, while pitched roofs are if the pitch is greater than 3:12.

This ratio defines the pitch or slope of the roof. The first number - 3 - refers to the number of inches the roof rises (vertical rise) per 12 inches of depth toward the roof top (the run or horizontal span) - the second number.The higher the pitch, the more visible the pitch becomes when looking at the roof.

The construction of a flat roof allows the use of several types of roofing materials, which we will discuss in a moment. But it can also cause numerous problems. The biggest concern with flat roofs is standing water. Sloping houses have an advantage because the slope allows water to drain away. Although a flat roof with a ½"1" pitch will drain most of the precipitation, it will not drain all of it.

Pooling Water Issues

A professional contractor must ensure that proper drainage is installed to ensure water does not collect on the roof as standing water can cause many problems for flat roofs.

Water puts additional stress on the affected areas, which can overload the structure. Areas that hold water for too long are at greater risk of collapses, cracks and leaks.

Leaks can also cause structural damage, potentially leading to mold, mildew, or wood rot. And due to the construction of most flat roofs, it's often difficult to locate the damaged area in order to make repairs. These problems can lead to potentially huge repair costs.

Choosing the right material for your flat roof reduces the likelihood of those horrific travesties. So let's take a look at what material might be right for your home.

Built-up Canopy (BUR)

Built-up roofing - referred to as tar and gravel - is one of the oldest coverings for flat roofs. Modern advances have meant BUR roofs are less common, although they are still used in commercial buildings and residential homes.

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Built-up roofing consists of layers of roofing felt covered with modified hot asphalt. Each layer of material can give your roof a five-year lifespan, up to 30 years. You can apply a BUR roof in three, four or five layer systems.

A layer of coarse gravel is placed on top of the materials to protect against UV damage, improve thermal regulation and aid in energy efficiency. It is also a fire retardant material for fire protection. Modern techniques include the use of additional top layers, such as B. an in-situ reflective coating or a granular cover sheet. These materials increase the UV protection and thermal insulation of the roof.


The cost of installing a tar and gravel roof can range from $3,750 to $6,750 or $2.50 to $4 per square foot ($250 to $400 per roof area - 100 square feet).

Attention:Odor installation.

Applying a BUR roof requires labor-intensive application using hot applications, meaning using a blowtorch or asphalt-covered hot mop. Unfortunately, this installation method leaves foul odors that can be harmful to people. Many businesses with regular customers and most homeowners will shy away from BUR roofing due to the chemical release from flare installation and will seek other alternatives.


  • Multiple layers of material for durability
  • You have the choice of how many layers to apply
  • The top layer of gravel provides UV protection and prevents damage to the underlayers
  • Regulates thermal energy


  • Labor intensive application
  • The installation causes harmful odors

Pro tip:There are several factors that come into play when it comes to the cost of all the roofing materials we discuss in this list. Things like the size of your roof, the complexity of the roofline, your location, obstructions like chimneys, air conditioners, vents and other items you can't remove, and whether your old roof needs to be torn down first.

Modified bitumen roofing

Unlike BUR roofs, which consist of multiple plies (layers), modified bitumen consists of a single layer of material – single ply. The single layer of modified bitumen consists of polymer modified asphaltic bitumen reinforced with a durable material such as fiberglass, polyester or a combination of both.

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Ease of installation makes modified bitumen an excellent material for DIY roofing jobs. MB comes in a rolled sheet 3 feet wide and up to 36 feet long. After laying a base course, unroll and seal the modified bitumen membrane.

Older MB types required the use of a torch to heat the material to create a tight, impenetrable seal. But newer designs have adhesive strips that use a peel-and-stick application technique, allowing for safer and faster installation. It is not uncommon to see hot-mopped asphalt or cold-applied adhesive. The torch method is rarely recommended due to the risk of fire.


You can expect to be in the $4 to $8 range. If you hire a contractor, plan to spend $3 to $7 per square foot for the labor and an additional $1 to $2 per square foot if you want more than one shift.

Attention:Large color selection.

Modified bitumen also comes in a variety of lighter colors, giving it greater reflectivity. So you will see savings on your energy bills. MB is leak-proof, tear-resistant, seamless and weather-resistant (due to the five-layer construction). And it's not only easy to install, but also easy to repair with bitumen patches.


  • Easy to install and repair
  • Self-adhesive options available
  • High reflectivity
  • Multiple color options


  • Not as durable against thrown up debris or foot traffic
  • A shorter lifespan of 10 to 20 years

Pro tip:Modified bitumen has two types of polymers - SBS (Styrene Butadiene Styrene) or APP (Atactic Polypropylene).

  • SBS (Styrol-Butadien-Styrol)

SBS gives MB a more rubberized texture and therefore more flexibility. In addition, this synthetic rubber modification offers better resistance to strong winds, aging, oxidation and temperature changes. And it will not crack from the stress caused by contraction or expansion.

The application of SBS modified bitumen can be done by using hot wiped cold glue or with self-adhesive backing. This material requires less heat to melt for installation, allowing for faster installation for all three methods.

  • APP (Ataktisches Polypropylene)

APP gives the tarmac a more plastic quality that is melted into liquid wax with a flashlight and then wiped over the roof during installation. Because of its high temperature tolerance and easy melting, APP is a popular choice for smaller residential rooftops and commercial buildings.

APP modified bitumen is more flexible at lower temperatures, allowing resistance to stresses caused by temperature changes. And it has higher UV resistance and insulating layer for better energy efficiency.

Single layer membrane (EDPM, PVC, TPO)

A single-ply membrane is laid directly onto an approved substrate, allowing for faster installation and lower costs. Single ply products have a longer lifespan and better performance than BUR roofs, making them a popular choice for flat roofs. There are 3 commonly used types: PVC, TPO and EPDM.

PVC - Polyvinylchlorid

PVC - also known as vinyl - is a blend of chlorine and ethylene to create a fireproof, waterproof and recyclable roof covering. It was the first single-ply membrane to receive ASTM International (ASTM D4434) safety standards.

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This single-layer membrane has a reinforcement scrim covered with two layers of PVC. The top layer offers flexibility and UV protection, while the bottom layer, made of black or gray PVC, has a higher concentration of plasticizers.

PVC applications can be ballasted, glued or mechanically fastened and have a service life of twenty to thirty years with minimal to no maintenance. And because PVC is fire, puncture, drop and impact resistant, with 80% solar reflectance it's one of the most durable materials you can use for roof protection.


If you choose to install a PVC roof, you can expect to pay anywhere from $4 to $7 for the installation. But the price can go up to $8 to $12 or more per square foot depending on the thickness.


  • Long service life, low maintenance
  • Multiple colors to choose from (black, grey, cream, white, tan and others or patterned to look like traditional clapboards)
  • High sun reflection


  • It can shrink over time and potentially cause leaks if the corners lift
  • The older the roof gets, the more prone it is to cracking and punctures from the cold

TPO – Thermoplastisches Polyolefin

TPO is a white fabricated membrane made from Polypropylene and Ethylene-Propylene - two rubbers - to produce a flat, single-ply sheet. The white color allows TPO to better reflect solar heat, allowing for easier interior cooling.

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Installation is a simple process using mechanical fasteners or adhesive strips. And because of the flexibility, TPO is an ideal product for roofs with odd angles and obstructions.

The single membrane of a piece of TPO consists of a cover layer and a core membrane. The top layer consists of 75% TPO polymer mixed with 25% to 35% flame retardants, UV stabilizers and a small proportion of pigments. The core is also TPO, but with 15% recycled content and no UV protection (not required).


TPO can cost $5.50 to $6 per square foot depending on thickness.


  • The flexibility allows it to be used on roofs with unusual angles or obstacles
  • High sun reflection
  • budget friendly
  • Resistant to mold, mildew, algae, dirt and corrosion
  • Recyclable


  • Extreme heat can cause leaks, tears and broken seams
  • A shorter lifespan of 10 to 20 years

Pro tip:If you enjoy using products made from recycled materials that are 100% recyclable after use, then TPO roofs could be your key to doing your part to save our planet.

EPDM - Cured Ethylene Propylene Diene Monomer

EPDM is a type of rubber roofing that is a suitable replacement for using BUR roofing. EPDM has been used for roofing membranes since 1965.

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EPDM roofs are available in black or white, with options for reinforced or non-reinforced. It is available in slabs from 10 to 50 feet wide and up to 200 feet long with thicknesses from .045 to .9.

About 50% to 60% of EPDM materials are made up of equal parts carbon black (UV protection) and polymer (for flexibility).

The other ingredients make EPDM fireproof and stable. Installation can be done with mechanical fasteners, an adhesive or by a ballast system - using pavers or natural stone to hold the material in place.


EPDM can cost you anywhere from $6.50 to $12.50 per square foot for a standard flat roof.


  • High UV resistance
  • Reflective surfaces reduce energy costs
  • easy installation
  • Resistant to impact, fire, heat, strong winds and thermal shock


  • May swell when exposed to oils or solvents
  • Reinforced panels may delaminate when exposed to water

SPF - Polyurethane Foam Spray

SPF - Polyurethane Foam Spray Roofing is an excellent solution for liquid applied systems for flat roofs as it can get into every nook and cranny to completely seal the top.

SPF is also easy and quick to apply and can be applied over existing roofing materials such as clapboard, metal, roofing or any suitable substrate. Polyol and isocyanate chemicals combine and come out as a sprayable liquid foam.

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After the roof has been thoroughly cleaned to remove all debris, the roof is pumped with a foam syringe. Upon contact with the roof, the foam expands to a height of 1 to 1.5 inches to create a watertight seal.

Once the foam has dried, one or more elastomeric or silicone coatings are placed on top to protect the roof from fire, UV damage and the elements. First there is typically the SPF layer, a base layer, then a reflective top layer. Some construction companies even fill the foam layer with granules.

The benefits of an SPF roof include improved energy efficiency (with an R-value of 6.25 per inch) - many of which can be considered cool roofs - a seamless construction to seal, low maintenance and repair requirements and a long service life of 20 years, with additional years possible to recoat.

These roofs must be professionally inspected twice a year. And you need to give it a thorough survey after heavy storms.


SPF can cost $3 to $4.50 per square foot to install, including materials and labor. Although it is possible to build an SPF roof yourself, most experts recommend letting a professional do the job to ensure your roof is installed properly and is guaranteed.


  • Easy to install and repair
  • Low maintenance
  • High R-value for better energy efficiency
  • Applies to most materials and saves money tearing down old roofing


  • Limited application window (requires dry, warm weather)
  • SPF roofs may not hold up well against windborne debris and birds

BUR vs. MB vs. Single-Ply vs. SPF

If you put all these materials side by side, you will see some similarities and some differences.

While BUR is one of the oldest and most trusted roofing methods, the worst part is the installation process. However, modified bitumen gives you all the benefits of BUR without the harmful chemicals and is the easiest to install yourself.

Single-layer TPO material offers the most budget-friendly choice of the three types. Both EPDM and PVC offer high reflectivity for solar radiation. SPF offers the best waterproofing, but requires a top coat to protect the foam from UV rays, impact and other damage.

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