Proper roof installation is the key to a functional and reliable roof. Indeed, although roofing materials, especially corrugate metal roofs, are very durable, poor installation can render the structural integrity of the metal sheets unhelpful.
How you fasten the screws (we don’t recommend nailing) is especially important. Roofing requires hundreds to thousands of screws and fastener sites and seams, depending on the type of roof.
There are many types of screws. You need to use the right screws in the right place to make sure your roofing material stays in good condition. Different screws work well for different materials. Be sure to use screws that will not let moisture get into your home.
This guide focuses on where the screws should go – the metal ribs or the flats. We’ll also discuss how to choose the right fasteners to facilitate proper roof installation and other metal roof installation tips to ensure the highest quality of roofing.
Where To Put Screws On Metal Roof – On Rib Or Flat?
Most U.S. metal roofing manufacturers say that you should put screws into the flat areas rather than the ribs. The flat offers a solid wood surface beneath the roofing sheets, resulting in a stronger, safer, and more secure seal. On the rib, the screws tend to loosen over time when you run a rake across them, especially during snow season.
However, there’s a lot of debate on this issue. For instance, proponents of flat installation constantly stress the need to follow manufacturer recommendations, which, as we’ve seen, vouch for flat installation.
Meanwhile, the proponents of rib installation argue that putting screws in the flat region subjects metal roofs to more potential leakage, given that water is naturally directed to the flats.
Then there are the fence-sitters who encourage roof installers to use their best judgment, arguing that rib and flat installations are the same.
We believe that flat installation offers the most advantages and comes with the fewest risks. But, of course, ribs have many advantages too. But the disadvantages far outweigh the benefits. So let’s look at some of the pros and cons of each option so you can see why rib installation is your best bet.
Pros and Cons of Installing Screws on Roof Ribs
Flat installation means installing the screws on the raised section of the roof. It’s the preferred method in corrugated metal roofing because the low points in a corrugated roof don’t offer enough room for nailing. Unfortunately, in-the-rib screwing is impractical for ribbed metal roofs.
Advantages
- Better protection against down-roof water: The biggest advantage of screwing the roof on the rib is it protects the underlayment and screws from down-roof water. It also reduces the risk of potential leaks because water naturally flows down the “valleys” or flats in ribbed roofs.
- Some roofs don’t offer enough flat space: In applications where the space between the ribs is tiny, screwing on the flats may not be very easy. In such circumstances, it makes more sense to screw on the raised ribs for ease of roof installation, if nothing else.
Disadvantages of Rib Installation
- Negatively impacts the sheer strength of the panels: Placing screws on the rib leaves a 5/8 to ¾ -inch gap between the underside of the high rib and the wood framing below. The screw can flex within this space, reducing the sheer load-carrying capacity of the sheathing system.
- Risk of leaks around screw cranks: The flexing of screws in the gap between the rib and the wood framing below allows steel panels to move slightly under wind or seismic loads. This can result in slots in the steel around the screw shanks over time, potentially causing leaks.
- Weaker roofing attachment: The fact about three-quarters of the screw length goes to waste (sits idle between the rib and the wood framing) means you don’t get the strongest roof attachment. The screws can more easily pull out during strong winds and storms.
- Higher risk of damaging the rib, and roof: Finally, there’s a higher risk of damaging the ribs and even the roof if you screw on the rib. Why? Because there’s no support below the rib. The space under the rib means any hint of over-tightening can collapse the rib. This usually forces contractors to pre-drill the holes before screwing, which only prolongs time spent on the project.
Pros and Cons of Screws in the Flats
Having screws in the flats, i.e., the space between two ribs, has several disadvantages. However, the advantages are more compelling.
Advantages of In-Flat Screwing
- Stronger roof attachment: The biggest advantage of on-flat screwing is a very tight seal between the roofing sheets and the wood framing below. A strong attachment makes it more difficult for strong winds to pull off the roof.
- Less risk of roof tear during installation: In-flat roof installation provides a support base in the form of the wood framing under the metal roof, significantly reducing the risk of roof tears during installation. Of course, the support frame also enables greater accuracy.
- Reduced risk of screw tilting: Screwing the roof requires precision. If you’re not careful, the screws may tilt, thus stretching the screw hole. If the stretched screw hole is bigger than the washer, the seal is broken, opening up gaps for roof leaks. In-flat installation significantly reduces the chances of screw tilt.
- It holds the roof underlayment better: Finally, most contractors use roof underlayment for increased waterproofing. Roofing underlayment is made of asphalt or synthetic materials and offers extra protection against weather elements, such as UV rays. Screwing on the flats rather than the ribs helps reinforce the underlayment in place.
Disadvantages of In-Flat Screwing
- Risk of leaks around the screw: The main downside of in-flat roof screwing is an increased risk of leaks from runoff water since water naturally flows down the roof via the flats. So, you must take extra steps to prevent rainwater penetration.
Additional Metal Roof Screwing Tips
Now that we know that it’s best to screw metal roofs in the flats let’s look at some of the best practices to ensure the best installation job.
Don’t under or over-tighten the screws
This might seem trivial, but if you don’t get it correctly, the roof will leak, or worse, you may damage it. The correct tightness is when the rubber washer, smaller than the metal cap, spreads to the edge of the metal cap and not past it.
Install screws straight; not sideways
If you notice that screws appear sideways on a roof, it’s because they were installed sideways. The problem is that tilted screws don’t permit the rubber washer to seal correctly. This can leave spaces around the seal, leading to leaks.
Remove metal shavings
Metal shavings created due to cutting and drilling roof panels are called swarfs. So, what’s the problem with swarf? They tend to rust very fast, often causing red corrosion spots on the roof, permanently staining the roof. Fortunately, you easily sweep away the swarf with a broom or brush.
To pre-drill or not?
Ideally, you don’t want to pre-drill. For one, it takes a lot of time to pre-drill roofs. Secondly, pre-drilling causes new issues if you’re installing the roof over metal purlins because you need to match the holes and locations in the metal purlins. However, feel free to drill if you must.
Use the correct tools
The only tool you should use to fasten roof screws is a screw gun – not a drill or impact driver. Why? Because drills and impact guns increase the risk of over-fastening and potentially damaging the roof.
Alternatively, you may under-fasten the roof, resulting in leaks. So, attach the fastener to a variable speed screw gun with an adjustable clutch and a depth control sensing control feature. Here’s how to choose the right screw fastener.
Use a chalk line for accuracy
It’s much easier to maintain a straight line of screws from one end of the roof to the other with a chalk line. We recommend a bright-colored chalk line.
More importantly, don’t forget to erase the chalk line once you’re done. Don’t assume the rains will wash away the lines.
Advantages of Metal Roofing
Metal roofing is one of the oldest and most popular roofing materials worldwide. Although shingles lead in popularity, metals offer many advantages that are hard to ignore;
- Longevity: Metal roofing materials are extremely reliable, lasting 40-70 years, assuming good installation and maintenance. On the other hand, asphalt shingles last 12-20 years.
- Durable: Many metal roofs can withstand winds up to 140 miles per hour if installed properly. Many modern metal roofs also don’t rust or crack and are highly impact-resistant, depending on the type of metal.
- Low maintenance: Unlike shingles, metal roofs are very low maintenance. You only need to inspect the roof every few months to ensure that it’s clean and free of debris.
- Energy efficiency: Metal roofs are very energy efficient. They reflect the sun’s UV light and infrared rays which can help reduce home cooling costs by up to 25%.
- Eco-friendly: Metal roofs contain recycled content that ranges from 25% to 95%. Plus, metal roofs are recyclable at the end of their life. In contrast, most shingles become waste when they’re no longer usable.
Importance of Proper Roofing
Unfortunately, it’s impossible to enjoy some of the above benefits without proper roofing installation. It doesn’t matter the metal quality; if you don’t install the sheets correctly, that’s the day premature roof failure begins.
Some of the dangers of poor roof installation include;
- A short roof life
- Voiding the manufacturer warranty
- Persistent safety challenges
- Frequent and expensive roofing repairs
What’s Improper Roof Installation?
A roof is properly installed when all the roofing components, accessories, and materials are installed correctly.
Therefore, a roof is improperly installed if just one of the parts is incorrectly installed. The main causes of poor metal roof installation include;
- Poor choice of installation materials
- Poor craft
- Poor attic ventilation
- Working in poor weather conditions
- Improper nailing or screwing techniques
Still Worried? Start by Getting the Right Metal Roof
If you’re worried about the inherent challenges of installing roofs, you can remove some of the worries by getting the right metal roof.
- No exposed fasteners: Get a roof with no exposed fasteners as this guarantees few easy options for water to penetrate.
- Wind-resistance: A few new metal roof systems can withstand wind gusts speeds equivalent to a major hurricane.
- Engineered to expand/contract: Modern roof metals “float” on their mounts as temperatures rise and fall to guard against potential damages from natural expansion and contraction.
- Durable and long-lasting: Get a metal roof designed to last a long time. Fortunately, many modern roofs can last up to 70 years.
Metal Roof Screws On Rib Or Flat FAQs
Can you put screws in the rib on a metal roof?
Yes, you can put screws in the rib of a roof. However, it’s not ideal for many reasons. For instance, putting screws on the roof’s ribs increases the chances of over-tightening and potentially damaging the roof.
Where should the screws go on a metal roof?
Ideal, the screws go on the flats. In-flat screwing reduces the risk of damaging the roof. It also ensures a stronger attachment between the metal roof and the wood framing below.
How should a metal roof be screwed down?
There are two broad categories of metal roofs – standing seam and screw-down. Screw-down roofs are screwed through the metal, whereas standing seam panels are fastened under each rib.
What is the screw pattern on a metal roof?
Generally, the screws are spaced 12-18 inches on the center such that every third corrugation has a screw, including both sides of the panel side-lap.
Can you put metal roofing on a flat roof?
Yes, you can put metal roofing on a flat roof, such as over the porch. Of course, a few constructors don’t recommend it. However, you can have a beautiful and durable metal roof on a flat roof as long as you’re prepared for the added maintenance requirements.
Summary
Generally, screws on a ribbed roof go on the flatbeds rather than the ribs. It ensures a firmer attachment for better protection from strong winds. Additionally, in-flat screwing reduces the risk of roof damage from over-tightening.