Metal Roof Repair Solutions: How to Solve Your Leaking Metal Roof Problems

Some common metal roof issues:

Before we jump into the areas where metal roof leaks develop, let’s look at a few of the major design characteristics of a metal roof system.

Metal roof systems can be installed as an architectural metal roof assembly or as a structural metal roof assembly. The primary difference between the two is the use of a structural roof deck.

An architectural metal roof system is installed over a separate structural roof deck. These systems can be found on most residential applications. They may also be found on commercial buildings such as shopping centers where there is a separate deck that supports the metal roof panels. The main characteristic of this type of metal roof system design is that there is a separate structural deck that supports the metal panels.

A structural metal roof system is just as it sounds. This design uses the metal roof panels as both the structural deck for the roof as well as the waterproofing system for the building. These metal roof systems are typically found on pre-engineered metal buildings. These metal roof systems are installed using clips that attach the panels to the horizontal purlins for the building. There is normally a batten insulation that is laid across the purlins before the metal panels are installed.

A separate design characteristic of a metal roof system is the slope. Metal roof systems can be installed in either a steep slope or low slope application. Forgetting to consider the slope can be a major source of problems for metal roof systems.

It is important to consider the slope of the roof when designing, installing and maintaining a metal roof system. The NRCA (www.nrca.net) defines a low-sloped roof system as any roof with a slope less than 3:12. All other roof systems are considered steep sloped.

Hydrostatic metal roof systems are designed to hold water until it can drain. These roof systems are capable of holding water without the roof system leaking. Typically these metal roofs are found on larger pre-engineered metal buildings. These larger structures are more costly to design with a steep sloped roof assembly. Additional hydrostatic metal roof systems can be found on residential applications. Tin and copper metal roofs can be installed with soldered flat seams in a hydrostatic system.

Hydrokinetic metal roof assemblies are designed to shed water. These systems are designed for steep slope applications. Steep sloped applications are found on residential and commercial applications where water cannot remain on the roof system. If the water is retained on the roof system it can create hydrostatic pressure forcing water into the details and creating metal roof leaks.

Mistakes in the design and installation of a new metal roof are sources of major problems. Typically the areas where problems occur are not in the system selection. The majority of the problems that cause metal roof leaks are related to the details used to finish the metal roof system. These mistakes are not immediately evident after the installation. They may take time to develop.

Here are five of the most frequent problems encountered during a metal roof condition assessment.

It is difficult and sometimes not possible to make metal roof panels that extend the full rafter length of the building. In some designs the project designer will limit the length of the panels based on expansion and contraction.

As a result of the restriction on panel length, the installer has to install horizontal seams into the roof system. These horizontal seams run perpendicular to the standing seams in the metal roof.

Horizontal seams are prone to separation over time. In hydrostatic metal roof systems, this can create an opening that allows water to enter back into the building.

Metal roof systems are prone to expansion and contraction. This is a result of the metal panels moving because of temperature changes. This movement creates stress at points of attachment as well as at the penetrations through the roof system. The stress leads to the breakdown of the flashings at the penetrations which results in roof leaks.

Metal roof systems are constructed by attaching individual metal panels together at the seams. Once the metal roof systems are installed they are very difficult to remove and disassemble.

Unlike an asphalt shingle system they do not disassemble to allow for a repair of penetration flashing. This makes long-term repairs more difficult to address especially if the penetration is installed after the metal roof is installed.

Metal roofs are made from a wide variety of materials. These include steel, aluminum, tin, copper and zinc. Some of these materials are subject to oxidation. Most metal roof panels are made from sheet metal that has been coated with a protective surface. Over time this coating can wear away leaving the metal panels to oxidize.

Surface oxidation can lead to problems. These problems can include structural failure if the metal roof system is a structural system. Oxidation also impedes repairs. Metal panel oxidation at exposed fastener heads can make sealant application difficult.

Metal roof systems typically include a combination of exposed and concealed fasteners. These fasteners can be nails or screws. Exposed fasteners typically have a neoprene washer that seals the fastener head to the surface of the metal roof panel.

Overtime fasteners have a tendency to back out of their seated position. This can be for various reasons. Wind uplift can lead to fastener back out. Metal panels will vibrate under wind conditions leading the fasteners to back out. Freeze-thaw can also lead to fastener back out. As the neoprene washer dries out water can enter in. In winter time conditions the water can freeze and expand leading to the fastener back-out.

Roof systems need to terminate into other conditions on the surface of the building. These conditions include rising wall details where the roof system matches into other surfaces. An example of this would be a metal roof system ending into a rising wall below a sign band on a shopping center.

This is an area where weakness typically develops. In many cases it is because of poor detail from the original installation. These details require closure strips to prevent water from blowing back into the detail. Contractors may forgo the installation of this closure strip. Initially the underlayment waterproofs the roof system against the blow-back. As the underlayment ages moisture can penetrate into the roof system.

There are other sources of potential metal roof leaks. These five are very common sources that can be checked initially. Knowing where to look for potential leaks is only half of the battle.

Now let’s look at some metal roof repair and replacement options and solutions.