Flat and Low Slope Roof Retrofit

By design, flat roofs with conventional membrane roofs have a host of problematic conditions. For example, their inability to shed rainwater promotes premature failure of the weathering membrane and its substrate.

They are also subject to harsh conditions caused by membrane deterioration from UV degradation, thermal expansion/contraction, ponding water and infiltrated trapped moisture that freezes in the winter and steams in the summer.

The result is constant maintenance, unexpected patch and repair work as well as inevitable roof replacement. Conventional tear-off and roof replacement is not a long-term solution.

View Related Files
Click image to enlarge

Great for









Low Slope Retrofit Roofing Systems

McElroy Metal Retrofit Roofing Systems provide long-term life expectancy and reduced life-cycle costs. In many cases, the cost difference between a conventional roof tear-off and replacement compared to a retrofit metal roof system is a return on investment which can be recouped in just a few short years. As an added plus, McElroy Metal Retrofit Roofing Systems provide curb appeal which simply cannot be achieved with flat roofs.

Building Owner Benefits

  • Decades long service life
  • Reduced maintenance
  • Energy savings through reduced consumption
  • Metal roofing is an ideal host substrate for solar photovoltaic panels
  • Increases wind and snow storm resistance
  • Possible reduction of insurance premiums
  • Improves value of your building

The Contractor’s Advantages

  • Easy to erect framing systems
  • Designed by in-house McElroy Metal engineering staff
  • Proven and tested standing seam metal roofing systems
  • All materials manufactured by McElroy Metal
  • Quicker than normal turn-around times
  • Reduces landfill expenses for disposal of existing materials 

Additional Information

McElroy Metal Retrofit Roofing Systems are engineered to adapt to the existing roof’s structural support system whether constructed of steel, concrete or wood. The importance of engineering the new retrofit framing system is hallmark to the overall project. 

Download The McElroy Metal Retrofit Roofing Guide to Learn More

Common Retrofit Assemblies

The most common framing assembly for a metal roof retrofit is the Post and Purlin system. As shown in the following illustrations, the system can be employed for installation over existing roofs with steel or wood framing as well as structural concrete systems.

The metal roof retrofit system is installed over steel bar joists that are spanning parallel to the new roof slope.

Adaptation to Steel

The Post and Purlin system adds a continuous base zee, which enables it to be installed over steel bar joists that are spanning perpendicular to the new roof slope.

Adaptation to Wood

For existing buildings with wood framed roofs, the Post and Purlin system uses a continuous base zee installed perpendicular to the existing wood joist. The base zee is required for these types of roofs, regardless of joists' span direction.

Adaptation to Concrete

For structural concrete roofs on existing buildings, the Post and Purlin system uses base shoes and posts that are installed centered over the existing concrete beams. When the beams span perpendicular to the new roof slope, a base shoe is still used, dependent on the spacing of the beams in relation to the retrofit purlin's span capacity. Otherwise, a continuous base zee would be included in the system.

Similar in concept to the Post and Purlin system, McElroy's Wide-Span framing system offers a unique method for specific applications where the existing roof's primary support systems are parallel to the new roof slope. In this illustration, a continuous base zee is placed directly over the existing primary framing (beam or load-bearing walls). Adding a continuous zee rafter supported by posts that are installed directly over each existing joist, will enable the new zee purlins to be placed as needed to satisfy design wind and snow loads. This system can easily be designed for purlin spans up to 30'-0" using 6" to 10" deep zee purlins.

Related Files

Get A Submittal Package

Customize your submittal package

Click on your desired documents below to select them for your package.

General Product and Warranty Information

Safety Data and Material Safety Data Sheets


Samples & Color Charts

Request physical samples and color charts. All items will be sent out via UPS ground unless otherwise specified.

Request now



Unlike asphalt shingles, which need to be replaced every 12-20 years, metal roofing can last up to 60 years with very little need for maintenance. For many homeowners, a metal roof is a true “one and done” solution they won’t have to worry about replacing in the future.

Learn More

Metal roofing actually reflects much of the sun’s heat and energy. While conventional shingles absorb much of the sun’s heat, metal roofing can actually reduce cooling energy costs by as much as 20%. That’s because the coating used on modern metal roof panels incorporates special pigments that reflect the sun’s energy and release heat that is absorbed throughout the day.

The odds of a lightning strike hitting a metal roof are the same as any other roof, regardless of material. In the event that there is a lightning strike, however, metal roofing will not ignite and catch fire since it is not combustible.

Read More

Far from it. Studies conducted by the Insurance Institute for Business & Home Safety (IBHS) have found that metal roofing is far less likely to be punctured by hail than conventional asphalt shingles, withstanding even golf ball-sized hailstones with only cosmetic damage.

Metal roofing consistently outperforms shingles when it comes to resisting harsh elements. In addition to being fire and hail resistant, metal roofs are also effective against extreme winds. Many insurance companies recognize the durability of metal roofing, offering discounts for structures with metal roofs.

A class 4 roof is an impact-resistant roof and will perform will when exposed to hail.

Learn More

Get our best tips and tricks for how to measure a roof for metal roofing.

Learn More

Metal roofing is an energy efficient, environmentally friendly roofing material that offers cost savings and a long lifespan.

Learn More

It is safe to walk on a metal roof. Get answers to the most common questions about how to walk on metal roof tiles.

Learn More

Yes! Get four reasons why they are.

Learn More

Asphalt saturated, roofing-tar paper, or synthetic?

Learn More

Yes! Solar panels and metal roofing are a great match!

Learn More

Oil canning is something you see when a metal panel appears wavy or distorted.

Learn More

Yes! Installing metal roofing over existing shingles is an excellent way for building owners to not only maximize the longevity of their new roof but also to save on roof tear off expenses.

Learn More
Read More
Weathertightness Warranties

If your project requires a Weathertightness Warranty and you don’t already have a job specific Pre-Approval Form issued by McElroy Metal, click the button below to get started.

Contact Us →

Shop Drawing Service
Shop Drawing Service

Running short of time to complete your own shop drawings? McElroy Metal can help. Click the button below to provide us some basic information and we’ll be in touch soon to discuss your project specifics.

Contact Us →

Download Shop Drawings
Download Shop Drawings

If you’re creating your own shop drawings, click the button below to gain full access to our CAD and PDF Files.

View Drawings →

Find a Distributor/Contractor Near You

Whether you’re building a new home or planning renovations, a metal roof can deliver long-term cost savings and comfort. To explore your options and find the product that meets your aesthetic and budgetary needs, contact a McElroy Metal distributor or contractor in your area today. We can’t wait to help make your dream home a reality.

Find a Contractor

Related Products

138T Shingle Recover

Learn more

238T Metal-Over-Metal Recover

Learn more

Substructural Components

Learn more