What Causes a Metal Roof to Leak?

Metal roof material

The popularity of metal roofing

Maybe you’ve noticed a trend in houses with metal roofs, even in the city? There was a time that metal roofs were for barns and industrial structures only, not for a home. Yet, today, metal roofs are on every size and type of structure today. Why is there a sudden popularity in metal roofing?  Could it be the lack of metal roof repair needs or the unique look they offer a home? 

For anyone that is considering replacing their current roof with metal, there are many more questions than those. In this article, we will dive into this subject and find out just what is this metal roof craze all about.   

What are the disadvantages of a metal roof?

There is not a perfect roofing material for every structure. As popular as metal roofing has become, it has a few disadvantages that you should consider before having a metal roof installed on your home:  


Installation Cost:
  While metal roofing is not as expensive high-end tile, slate, or wood shakes, but when comparing metal to asphalt shingles, it is more expensive. One major offset to this is the long lifespan metal roofing offers compared to asphalt shingle.  So, while the immediate expense of installation may be high, think about the future and the amount of metal roof repair you’ll have (or not have).

Install Longer: Metal roofing can be complicated to install. In some cases, it can take two times as long even for the most experienced and skilled contractor. However, a metal roofing installation time is about the same to the sophisticated roofing materials like slate or wood shake.

Non-Resistant to Saltwater:  Metal roofing corrodes faster in an area where there are saltwater and fog.  If you live in a saltwater area, review the warranty and its specifications before going with a metal roof, which in most cases is 1500 feet or further. If you choose to ignore the specifications of saltwater proximity, you can expect to need metal roof repair in the future, sooner than later.

Limited Availability: The number of roofing contractors experienced and skilled at installing a metal roof isn’t as common as those with asphalt roofing shingles. Because most of the problems with metal roofing stem from the installation weren’t done correctly, it is important to find a roofing contractor with metal roofing experience. Choosing an experienced metal roof contractor will give you the reassurance they will be around for any metal roof repair you may need in the future.

What causes a metal roof to leak?

Yes, metal roofs are almost indestructible, but nothing is 100% indestructible. Here are six possible causes of leaking metal roofs that require metal roof repair:

Roofing Screws

Metal roofing is durable and leaks are few, but when they do leak, it is common that the roofing screws are the culprit. The metal roofing screws have a rubber washer under the screw head that is compressed into the metal when installed to create a waterproof gasket. However, things can go wrong such as:

  • Overdriven: A contractor can be overzealous in tightening the seal and break the rubber washer, pushing it out the sides of the screw. 
  • Under driven: This is the opposite of the overdriven screw and the contractor did not seat the rubber washer to the metal panel, thus it wasn’t compressed to create the seal.
  • Wrong angle: When a metal roofing screw is installed at the wrong angle the rubber washer isn’t flat to the metal and can’t create the seal needed.
  • Screws missed the frame or strut: When metal roofing screws miss the intended target of the wood frame or metal strut, they can’t create a seal the metal sheets. These are the most difficult leaks to identify.

Even correctly installed screws aren’t infallible. Areas where the summers are hot and the winter is bitter cold make the rubber washers degrade, losing their seal, something to consider when looking at a metal roofing and future possibility of metal roof repair.  

Stack Flashing

The stack flashings around the piping on metal roofing are susceptible to leaks. The piping is where the air vents, HVAC vents, and plumbing come through. If those pipes aren’t waterproofed correctly with rubber or rubberized material, they don’t create the needed seal. Because metal roofing contracts and expands with the weather, that sealant is necessary and must be flexible to move with the movement. 

Because these flashings degrade with exposure to the sun, they need to be resealed occasionally. However, when caulking, sealant, or tar is done incorrectly or too much, it can cause water ponding, which can create a leak. The best way to avoid the need for metal roof repair is to totally replace the stack flashings periodically. 

Sealant missing 

Sealants are installed in union with a metal roof rarely have the same lifespan as the metal roofing panels, therefore, they need replacing as part of roof maintenance. This includes any sealant under trims like counter flashings, metal ridge caps, pitch pans, reglets, roof transitions, and Z flashings. Periodically, these areas should be “topped off” as they wear down with specific metal roof sealant. Using any other caulk, like silicone, won’t adhere. Sealant for metal roofs will move with the metal panels in contracting and expanding, keeping their seal.   

Curb Flashings 

The HVAC unit installed metal roofs require a curb and there is little to no room for any error during the fabricating of the flashing for the curb to be kept dry. The uphill side and the 2 upper corners are difficult areas for the curb, especially for larger HVAC units because this is where water gets trapped and stands, eventually eroding the sealants, and starts leaking.

The more you caulk, seal, or tar the uphill side, the more water it will hold and require metal roof repair. Just like the stack flashing, the best way to avoid any possible leaking here is to replace the curb flashing periodically instead of resealing them. 

Overlaps and seams

Where two metal roofing pieces meet and create a seam by overlapping each other, creating a capillary draw can be susceptible to leaking. A Capillary Draw makes water travel uphill between the two joined metal pieces. This can be avoided or repaired with butyl tape or sealant, but again, if not applied properly, it can make matters worse, requiring a metal roof repair.

In any of these instances described above, it can cause the seams to be loose. High winds raising a loose seam and bending it or even remove a metal roof panel. Creating the need for a metal roof repair insurance claim

How do you fix a leaking flat metal roof?

As with any roof leak, you need to find the source of the leak first and the location will determine what method should be used for a metal roof repair. An experienced metal roofing contractor will use fasteners and will begin by inspecting each nail/screw row by walking on the row to keep from bending the metal.

Because walking along a roof is dangerous to the inexperienced, it is understandable why metal roof repair cost is high because it is best left to be done by an experienced roofing contractor who will have all the property metal roof repair products, supplies, and safety equipment. The process will go something of this order:

  1. Any nail/screw that is raised needs to be removed and replaced with a 1 1/2-inch aluminum metal roof repair screws with a hammer to drive it down.
  2. A urethane roof cement is then applied to the new screw-nail with a putty knife.
  3. Caulked seams and upper edges are then inspected and repaired or replaced as needed after removing any loose caulking with a wire brush. A urethane roofing cement is applied to the upper portions with a putty knife.
  4. Where gaps are found on the edges of the panel overlaps, and debris needs to be removed using a wire brush. Then apply a uniformed layer of metal-roofing base six inches in each direction of the gap using a paintbrush and overlap the strokes.
  5. Covering the base coat with a glass-membrane fabric next and then a top coat of urethane cement needs to be applied, six inches to either side.
red metal roof

What is the best sealant for metal roofs?

If you find that you’re needing a metal roof repair for your home, there are several products on the market and an experienced, qualified roofing contractor that works with metal roofing will know the best one for your home. Factors that they will take into consideration would be the age of the roof, the sealant used when the roof was installed, and the climate where your house is located.

While metal roof isn’t perfect and will never need maintenance or repair, it is a durable product that has withstood the hands of time for years. It has a lasting character that never goes out of style and will blend with any exterior décor. Dial (336) 823-6156 today for metal roof installation in High Point, NC.