When to Retrofit, Recoat, or Replace
Metal offers an array of benefits, whether it be as a wall or roof covering. In addition to its beauty, strength, aesthetic, and geometric design options, metal is 100% recyclable, containing a significant proportion of recycled materials. Metal can provide a broad range of reflectivity, and, naturally, requires less maintenance as compared to almost any other building enclosure material available on the market.
Furthermore, metal roofing offers the lowest cost of ownership throughout the lifetime of the roof as compared to other roofing systems due to the low maintenance costs and the physical nature of metal. Aluminum panel and coated steel systems, when properly designed, installed, and maintained, can last for more than fifty years. Even more impressive, exotic metals like stainless steel, zinc, and copper may last long over 100 years.
However, eventually, even the metal will come to the end of its serviceable life. When this time comes, the owner faces the decision of whether to recoat, retrofit, or replace the roof altogether. Every single of these options can provide considerable benefits when used in the proper application. But when is it best to recoat or retrofit a metal roof, and what needs to be taken into account when making the decision?
Determining the Main Issue and the Best Course of Action
Before identifying the right course of action, owners should get to the core of the issue. In order to do so, ask yourself a question, “What is wrong with the existing roof?”. Consider these potential questions as well:
- Is there enough insulation in the building envelope?
- Are there any minor leaks? Is moisture entering the building throughout the entire facility?
- Does the old roof still perform well, but appears faded or rusted?
- Does the owner want to upgrade the aesthetic appeal or want a new look for their building?
- Has work been conducted on the building that may have damaged the roof? For example, additions or alterations to the building or mechanical equipment.
- Is there noticeable damage to the roof from physical impact, ice, snow, wind, or from deterioration and age?’
Only once you can identify what is truly wrong with the roof, and what the owner’s expectations are, you can make the right decision of whether to recoat or retrofit.
To keep things simple:
- If the existing roof system has still good structural condition, but experiences some leaking due to poor detailing or sealant breakdown and surface rusting, retrofitting is likely an optimal option.
- On the other hand, if the roof is still in quite a good condition, only has small leaks at the seams, does not exhibit major or pin hole rusting, but just looks worn or faded, recoating the roof may be the proper course of action.
- If the existing roof exhibits significant rusting, is structurally compromised, or shows large amounts of saturated insulation under the roof panels, the right choice would likely be to remove the existing roofing system and install a new metal roof instead.
While these basic guidelines are simple, every roof requires a project-specific review in order to evaluate the existing conditions and properly find the right course of action for both the owner and the building. It is always best to consult an experienced engineer, consultant, or manufacturer’s representative to evaluate the existing condition and a scope of work that will suit the needs of the building owner.
Benefits of Retrofitting an Existing Metal Roof
Metal roof retrofitting can offer a broad range of benefits to a building owner. In addition to the time saved without having to remove the existing roof, the facility won’t need to be shut down due to the roof retrofit. Manufacturing facilities, schools, and food processing plants can experience significant negative operational and monetary effects if a shutdown is needed to install a new roof.
Without having to tear off the existing panels, a roof retrofit also reduces the total labour cost for the project. In addition to saving money on the initial installation, this provides an opportunity to reallocate the saved budget on a high-performance standing seam system. When planned and installed properly, these systems usually last longer and require less maintenance as compared to through-fastened metal panel roof systems, reducing the total cost of ownership throughout the roof’s lifetime.
Some older metal buildings may be lacking proper insulation within the roof system. More recent requirements of energy codes like the International Energy Conservation Code prescribe higher R-value. A retrofit offers a chance to increase the R-value of the roof assembly according to the code requirements, while increasing the comfort level and the energy efficiency of the building. If current batt insulation under the panels is falling apart or is saturated, the optimal option during a retrofit is to replace the insulation altogether with the new, code-required amount of insulation on top of the old roof panels and under the new ones.
Metal Roof Retrofit Methods and Considerations
According to Section 1511.3.1. Of the International Building Code (IBC) of 2015, “The installation of a new roof over an existing roof covering shall be permitted where any of the following conditions occur…” The second condition here is: “Complete and separate roofing systems, such as standing-seam metal roof panel systems, that are designed to transmit the roof load directly to the building’s structural system and that do not rely on existing roof and roof coverings for support, shall not require the removal of the existing roof coverings.”
Nevertheless, a professional structural engineer should be consulted with any retrofit project. The engineer should conduct a structural evaluation to ensure that the existing roof structure will be able to withstand the additional dead load of the retrofit framing and the new metal panels. This is especially important for pre-engineered metal buildings, which may not have enough capacity to withstand additional dead loads.
The most popular way to retrofit a metal roof is to use structural framing members, which fasten directly through the existing panel, into the frame of the roof structure. With this method, the additional load of the new roof is transferred to the structure instead of the existing metal panels. The framing will typically consist of 14- or 16-gauge steel, but could be thicker, depending on the project.
Usually, notches are cut into the bottom of these framing members, so that they conform to the seams or ribs of the existing metal roof. As a temporary measure for waterproofing, sealant should be applied to the head of all fasteners used to attach the framing, as they may remain exposed for a significant period of time before the installation of the roof panels. If needed, additional insulation can be installed between the new framing members before the panel installation.
A structural engineer can also plan the thickness, height, attachment rate, and spacing of the retrofit framing. Typically, the spacing of the new framing system is determined by the spacing in the purlins of the existing roof structure. The manufacturer of the new roof should provide the requirements for the attaching of the panel to the framing using uplift resistance testing, according to the FM 4474 or ASTM E1592 test standards, as outlined by IBC. A structural engineer can also be contracted to ensure the sufficient attachment of the new metal roof, using the test data and recommendations of the manufacturer.
Another metal roof retrofit method involves an overlay of a light gauge through-fastened metal panel or a single-ply system. This retrofit method is usually addressed by filling the flutes of the existing roof with insulation that is pre-cut to match the shape of the existing panel. The metal or single-ply system is then fastened to either a framing system attached to the building structure or to the existing panel.
Here, the attachment method should be designed according to the manufacturer’s guidelines and should be engineered separately for each project, as there could arise structural concerns, like wind uplift resistance or weight, that need to be addressed with the existing roof. In such applications, the pitch of the roof should be limited to 1:12 or more, or in accordance with manufacturer’s requirements. Lower slopes may not allow for drainage behind the seams, leading to maintenance concerns and premature breakdown of the seams.
Even though this method offers a lightweight option for retrofitting, additional weight is still applied to the roof. As such, a structural evaluation needs to be performed to make sure that the roof’s capacity for dead load isn’t exceeded.
Modified bituminous membrane systems may also be considered for roof retrofits, but this option adds a relatively high amount of weights, which is not practical and, most of the time, cannot be accomplished within the dead load capacity of the existing roof structure.
Other considerations that need to be kept in mind are flashing components, which should be at least 8 inches in height. Wall flashing, vents, mechanical units, etc. may need to be raised to reach the 8-inch heights. This may lead to additional project costs in case it wasn’t addressed during the design stage. If ventilation exists in the existing metal roof, it must also be carried through into the new roofing system. Failing to do so can lead to issues with building envelope performance, such as condensation.
Recoating an Existing Metal Roof
When the current metal roof performs well and remains structurally sound, but shows minor wear and tear at the seams, surface rust, faded finish, or just needs an update, a recoat of the existing roof may be the optimal solution. A new coating can offer a beautiful fresh look to a facility at a much lower cost, as compared to a retrofit.
However, prior to choosing this option, take note of the conditions of the building that may have led to the issues in the first place. If the current roof is leaking due to poor detail designs or a low-grade metal panel, recoating the roof won’t solve these problems. In addition, if the existing finish is flaking, fading, rusting, or staining due to abnormal or chemical atmospheric conditions, or if the existing paint gets damaged due to physical abuse, recoating will likely lead to another early failure of the roof’s finish.
When a recoating is determined to be the right solution, there are several considerations to keep in mind. In order to decide which coating is best, the conditions of the current substrate need to be evaluated by an experienced applicator or a coating manufacturer. The is a broad range of coating or finish options available on the market today, such as:
- Acrylic or acrylic latex finishes
- Field applied fluorocarbon paint finishes
- Solvent-based urethane coatings
- Asphaltic coatings
- Silicone coatings
- Thermoplastic coatings
- Solvent-based rubber coatings
An experienced high-performance manufacturer will assess the condition of the existing substrate, select the applicable product option for the project, and decide on the preparation required for the system.
As any experienced applicator or coating manufacturer will tell you, preparation is the most important portion of a recoating project. The preparation for metal roof recoating can be just as expensive as the labour costs associated with a retrofit project. However, the overall cost of materials for recoating is usually far less than that of a retrofit, making the overall recoating project more cost-effective.
Some common techniques and conditions for preparation include:
- Hand tool cleaning, such as sanding, chipping, or brushing for the removal of mill scale, loose rust, paint, or other foreign matter.
- Solvent cleaning for the removal of oil, dirt, great, or other soluble contaminants
- Power tool cleaning for more aggressive removal of the above substances
- Pressure washing
- Blast cleaning
- High-pressure water jetting
The Society for Protective Coatings (SSPC) provides the standards for surface preparation, which can be used as guidelines for the right surface preparation techniques and requirements. However, as mentioned earlier, it is still critical to consult with an experienced applicator or a coating manufacturer to determine which products and techniques should be used for each project.
When it comes to determining what to do with a metal that may be near the end of its life, there are a number of options to choose from. Retrofitting it with a new metal roof can offer decades of beauty and protection. Recoating the system – if the conditions allow – offers an aesthetic upgrade that may also help the roof to perform for many years to come. With either option, the project must be addressed individually and should be conducted with the help of a manufacturer’s representative or an industry professional to help avoid potential mistakes that could end up being quite costly.
However, once the correct course of action is determined, and the right design, product, preparation, installation, and maintenance plan is implemented, the solution will provide a business owner with time and money to focus on their business instead of the roof over it.