While metal roofs are known for the longevity - most lasting for 50 years or more, because they require a more skillful install they can be subject to some leaking problems throughout the years. If you’ve been responsible for a metal roofing system, you’ve most likely have had to deal with a leak from the roof.
Because of the unique interlocking nature of most metal roof systems, the issues that cause leaks are unique and as a result, the repair methods are also unique.
Most of the time, metal roofs are installed on residential buildings that have steep slopes - this saves the most money over the long haul from costly labor fees for dealing with steeper roofs and more frequent asphalt shingle roof replacements.
Other typical metal roof installations are over commercial and industrial buildings - you’ll often see them placed on churches, banks and other buildings that look to reduce overall maintenance versus traditional roofs.
If you’ve been experiencing leaks on your metal roof, then you’re not alone. Metal roofs can be prone to leaks in certain vulnerable areas.
Here are the common areas of problems:
- Open seams
- Open flashing
- Oxidation of Metal
- Fastener backout
- Open ridges or headwall flashing
- Loose counterflashing
- Improper installation
- Damaged panels
Metal roofs are usually installed as either an ‘architectural’ metal roof or as a ‘structural’ roof assembly. The difference between them is going to come down to the actual use of a structrual roof deck.
Metal Roof Design Types and How they Affect Leaks
Architectural metal roofs are installed over a completely separate structural roofing deck. What that means is that technically the metal panels and the decking of the roof are separate and fastened together. This is the most common type of installation on residential homes, but are also sometimes found on commercial buildings, such as shopping centers, where separate decks support metal panels.
However, structural metal roof systems are just like they sound (compared to architectural ones), these use metal roof panels as both the structural decking and the waterproofing system of the building. Usually you’re going to find this kind of install on a pre-engineered metal building with custom designs, shapes and needs. These are usually going to be installed with clips that connect panels to horizontal purlins for the building.
Hydrostatic & Hydrokinetic Design
The next important element of a metal roof is the actual slope of the roof. Metal roofs are commonly installed on steep slope roofs, but also find themselves installed in low slope situations.
When you’re looking at the cause of leaks on a metal roof, you have to consider the slope - and this is often overlooked during design, installation and maintenance.
Hydrostatic metal roof systems are designed to simply hold water until it can finally drain off. It’s entirely common and normal to see standing water on top of these systems, as they’re capable of holding water without a leak occuring. Usually this is going to be found on a large pre-engineered metal building. These are more costly to design with a steep slope assembly, but they can sometimes be found on residential homes.
Hydrokinetic metal roofs on the other hand, are designed to shed water. These are the systems that are most common on steep slopes, which are the most common on residential buildings, or in commercial situations where a roof simply cannot have standing water on the roof for any amount of time. If you have a hydrokinetic metal roof and there is standing water, then this will cause a problem where leaks happen directly because of hydrostatic pressure forcing water into the seams of the roof.
Most Common Areas of Metal Roof Leaks
What do all these details have to do with your metal roof leak?
Mistakes in design and installation for metal roofs are the source of the vast majority of major problems. Again, this is because metal roofing requires custom planning for each roof, rather than the rather routine task of installing a shingle roof.
What’s worse is that these mistakes are not always immediately evident after an installation, and can often take time to develop.
These are the top 5 metal roof leak problems:
- Openings in Horizontal Seams
- Openings in Penetration Flashing
- Oxidized Metal Roof
- Open Ridge / Headwall Flashing
- Fasteners Backing Out
Metal Roof Leak Common Causes In Detail
Horizontal Seam Issues (Openings):
Sometimes metal roof panels won’t extend to the full rafter length of the building. This ends up being a design flaw, which at times, the project designer has to limit the length of panels based on expansion and contraction during winter and summer months.
The problem is, horizontal seams tend to separate over time. In hydrostatic metal roofs, this creates an opening that allows water to enter back into the building, rather than drain away properly.
Penetration Flashing Issues (Openings):
Due to the nature of metal, metal roofs are more prone to expansion and contraction. As a result, the metal panels are actually moving because of the different temperatures that naturally occur between different seasons.
This movement puts stress at every point where pieces of metal attach to one another as well as in the penetrations throughout the metal roof system. This stress causes a breakdown of the flashings at the penetrations, which causes the roof to leak.
Metal roofs are all constructed by attaching separate, individual metal panels together at seams and interlocking them or otherwise connecting them together. Once the metal roof is installed, it’s very difficult to remove and disassemble, unlike asphalt shingles where you can disassemble a few to repair, and simply replace the missing shingles. Generally, for a metal roof a whole section is going to have to be replaced to do this kind of repair.
Metal Roof Oxidation
Usually the metal your roof is made out of is going to come from a variety of metals including steel, aluminum, tin, copper and zinc. Some of those materials can become oxidized over time. The vast majority of metal roofs are made from sheet metal that is coated with a protective surface to prevent oxidation, but over time the coating will wear away and leave the panels vulnerable to oxidation.
Fasteners backing out
Fasteners typically hold together a metal roof, and usually they come in a combination of both exposed and concealed fasteners. Usually these are either going to be the nails or the screws that physically hold everything together and they usually have a neoprene washer that acts as a seal.
However, over time these fasteners can slowly “back out” of their original position. This can be caused by excess wind over time, natural expansion and contraction “pushing” them out over time, even freezing and then thawing out.
Open Ridge and Headwall Flashing
Ultimately, any roof system has to end or “terminate” onto the surface of the building. These connecting points are often the most vulnerable of any roof system, because you have to match the connection between metal and and ‘wall’ material.
In many cases, poor attention to detail from the original installation causes a few missed spots that end up with leaks coming through (as these areas tend to see the most volume of water passing over them, since typically roof-wall connectors are right where water is designed to drain off the roof). Initially, waterproof underlayment helps protect the roof system against blowback, but as the underlayment ages, moisture can build up and penetrate the roof system, causing your roof to leak.