The roof of a steel building, or any building for that matter, provides protection from rain, reflects solar radiation, and is part of the aesthetic of the structure. How it is shaped can depend on anything from regional custom to regional weather. When the wind comes up and the hail comes down, the roof is the part of the building that takes the beating.
The roof has a big job. In order to meet it, you need your roof to be installed properly. The trick is to learn what makes a roof installation successful from the beginning.
Anatomy of a metal roof
A metal roof is made of panels supported by the purlins that make up the secondary frame structure. The panels are generally 22 to 24 gauge galvanized steel or aluminum and are fastened to the purlins with clips at pre-punched holes. These clips will typically allow for panel expansion and contraction without damage.
The seams between metal roofing panels can be lapped or standing; a standing seam roof is an excellent configuration on which to install solar panels. It is also an excellent configuration for shedding rain.
Training is your best bet
No matter the type of roof, your best defense against roof failure is a thoroughly trained installation crew. Workmanship errors are one of the main causes of roof system failures. If the roofing contractor has invested in proper training and has hired for experience, there will be fewer problems with installation.
With metal roofing, sheet metal expertise outweighs other roofing material experience. Metal roofing systems are quite different from other materials and workers used to wood framing may not possess the right skills.
Tips for roof panel installation
- In order to minimize end laps, obtain panels that are at the maximum length for your design.
- Overlap the adjoining panel laps by a minimum of six inches.
- Install a reinforcing plate, top panel strap, and sealant when overlapping adjoining panels.
- Make sure the seams interlock yet allow for movement for expansion and contraction.
Simply put, the higher the slope, the better water will shed from it. In some regions, a higher slope is needed to minimize ice build-up and allow snow to slip off easily as well. Very low slope roofs may hinder weather-proofing capacity.
Low-slope or flat roofs can have a tendency to allow water to puddle, giving it time to find any breach in the roof seal to start a leak. Seams, fastener points, and penetrations must be completely sealed to keep this from occurring.
The common minimum for roof slope is ¼:12 but for a quick shedding roof 2 ½:12 is more than adequate.
Waterproofing for low slope roofs
When a roof is close to flat, the design must take into consideration the roof load, standing water, and waterproofing at the seams and penetrations. If the roof panels are designed to join with doubled folds there is less chance of water leakage than for a typical lapped seam roof.
At lapped seams, penetrations, and fastenings, there is an increased chance of water working its way into the system. Everything must be completely sealed according to the manufacturer’s specifications to keep this from happening. However, if there is a great deal of expansion and contraction, the seal is a major area of failure.
Common problems in metal roof
Metal roofs are not foolproof and there are plenty of ways to show it. Some problems are primarily aesthetic; the roof performs perfectly well but it looks terrible. Other issues, of course, generally result in insurance claims for water damage.
Mismatched panel colors
Just like paint, carpeting, or any other mass produced item, there can be differences in color between batches. This is very noticeable when side-by-side roof panels are of slightly different shades. This can stem from slight changes in shade as the metal is galvanized to problems matching paint colors between batches.
Most of the time this is due to the roofing contractor using leftover materials from another job and mixing them in with the new materials ordered for yours. Find out if this is a common practice with your installer and make your preference known.
If the roof fasteners are driven into the wood furring strip rather than using the appropriate clips and pre-drilled purlins, there is a greater chance the fastener will back out of panel over time due to movement. Wood moves at a different rate than metal; if a metal roof has been fastened directly to wood, there will be movement mismatching that results in fasteners coming out of the roof and breaking any sealant they were coated with.
Using poorly galvanized fasteners and neglecting to properly seal the seam and fastener can produce rusty fasteners that fail. Besides complete failure, rusty fasteners are unsightly and can cause rust stains to run down along the panels as well.
Roofs constructed of low gauge metal can wrinkle or become wavy upon installation; they lack the necessary stiffness to lie flat. This is known as oil canning. Most often found on standing seam roofs with 26 gauge or thinner panels, in cold weather, the roof will look fine. However, the heat of summer, especially in southern climes, causes the metal to shift and buckle slightly.
This is mostly an aesthetic issue but can also signal the use of panels that are not as durable during hailstorms or high winds.
Nothing is worse than making a claim for a problem and finding out the warranty was somehow voided. As the roof is installed pay particular attention to the following so the work can be redone before the crew leaves.
- Panels that appear to have been forced into place
- Unsealed cut edges and jagged edges
- Fasteners driven too tightly into place (the area around the fastener will appear sunken)
- Incorrect sealant used around protrusions
- Wrong underlayment
- Incorrectly spaced furring strips
- Panels that appear wrinkled, warped, or dented from workers walking on unsupported areas
- Scratches that have not been sealed
Anytime something looks out of place or just doesn’t look right, bring it to the attention of the roofing contractor and get it fixed to your satisfaction.
Every project is different; these recommendations don’t cover every design and product. But they will help you determine the success of your installation and steer you clear of some of the most common mistakes. There is one last piece of advice that may save you some grief in the long run: do not hire for the lowest bid without doing your research on the contractor.