One of the most important factors in a proper roof installation is screw (or nail) spacing. The correct nail spacing holds the roofing sheets more firmly in position. Correct spacing is also critical to ensuring a level roof. Above all, an appealing screwing/nailing pattern makes your roof more and the home, in general, more beautiful.
Generally, it’s best to place roofing screws one and a half to two feet apart. Alternatively, make sure that every third corrugation has a screw, including both sides of the panel side lap. The idea is to place the screws close enough to ensure a firm roof installation and far enough not to distort or tear the roofing material.
Screws vs. Nails for Metal Roofing
Let’s begin by comparing nails vs. screws for metal roofing installation. Which is the better option and why?
Generally, many roof experts prefer screws to nails. Though nails are more common in metal roofing projects, screws offer plenty of advantages.
- Holding strength: The first main reason screws work better for metal roofing projects is that screws hold for much longer. The threads on screw shafts allow screws to hold onto wood for much longer. On the other hand, nails have smooth shafts that are more likely to pull out.
- Resistance to expansion and contraction: Another reason screws are a better fit for metal roof nailing is that screws withstand metal roof expansion and contraction better. Such contraction/expansion often causes nails to pull out slowly over time. The threads allow screws to resist such pull-out.
- Preventing roof leaks: Finally, screws resist leaking better than nails. The expansion/contraction mentioned above often results in spaces around the roofing nails, causing leaks. By withstanding contraction/expansion better, roofing screws significantly reduce the risk of roof leaks.
That said, though, roofing screws can be an excellent choice under certain circumstances. First off, screws are expensive to purchase. Therefore, if you’re looking to keep costs down, consider high-quality roofing nails.
Additionally, nails are easier to install. Whereas screws require technical know-how and special tools to install, anyone with a hammer can nail down nails. This makes nails the better option for DIY roofing installation projects.
What Happens if you Don’t Use Enough Metal Roofing Screws?
Once you’ve settled on screws for your metal roofing project, the next question is how many screws you need.
Many DIY roofing installers often wonder whether there are significant consequences of using too few or too many screws/nails on the roof. Yes, the consequences can be huge.
- Dangers of Too Few Roofing Screws: The main danger of using fewer screws than needed when roofing is that you may have a weak roof. A weak roof can come off anytime. Unfortunately, it also puts you and your family/guests in danger.
- Dangers of too many screws: The main downside of too many roofing screws per square meter when roofing is the high risk of roof damage. This is an even bigger concern when the screws expand and contract during extreme weather.
How Many Screws Do you Need for Metal Roofing?
Generally, you need 80 roofing screws for every roofing square, where one roofing square is equivalent to 100 square feet.
For instance, you need 0.8 x 10 = 8 screws for 10 square feet of metal roofing and 0.8 x 300 = 240 screws for a 300 square-foot metal roof.
Metal Roofing Spacing and Pattern Guide
The following are the recommended screw spacing patterns for standard metal roofing projects to help you determine how many screws you need.
What’s the Screw Pattern for ⅞-inch, Corrugated Metal Roofing?
Perhaps the biggest confusion arises when dealing with ⅞-inch corrugated metal roofing. That’s because different manufacturers recommend different faster placement spacing.
First off, we believe that you decide the best screw pattern based on whether you have the screws on the highs or lows of the corrugated roofing sheets.
Many people prefer installing the screws on the high as it makes installation easier. This method also allows water to flow freely down the roof and reduces the risk of roof leaks because the screw holes are on the high ridges.
However, we often recommend installing the screws in the troughs. Although it increases the risk of leaks because of flowing rainwater, screwing in the troughs guarantees a more secure connection. The screws are also less likely to distort the metal roofing panel.
7/8 -inch Corrugated Screw Location for Metal Roofing
The screw location on corrugated metal roofing depends on whether the screws go on the highs or lows and the screw line location. A screw line is a row of several screws placed a certain distance from the next row of screws.
Generally, when screwing in the highs on standard 37-inch corrugated roofing sheets, you need four panel screws per screw line, spaces such that you have a screw on every third corrugation.
Use the same approach for 39-inch roofing sheets too. The only difference is that you’ll have the final nail in the screw line goes on the fourth groove instead of the third.
The same approach works when screwing in the lows. For 37-inch roofs, screw four panel screws in every screw line to have a screw every three troughs. However, for 39-inch roofs, the fourth screw in the screw line comes in the fourth rather than the third trough.
- What’s the appropriate panel side lap for 7/8-inch corrugated metal roofs? You need two things on the panel lap. First, whether you’re screwing in the highs or lows, one lap screw must go where the panels overlap. Secondly, if nailing in the lows, use double-sided mastic tape along the visible edge of the overlapping roof sheet.
- 7/8-inch corrugated screw location for wall panels or metal siding: You need five panel screws and one lap screw for wall panels and metal siding. The lap screws are located 12-18 inches in the center of the corrugated sheets. This way, every third ridge has a screw, including both ends of the side lap.
What’s the correct Screw Pattern and spacing for R-Panel Metal Roofing?
The roofing pattern for R-panel metal roofing is straightforward – and this applies to both metal roofing and metal siding applications. The main difference is that you need additional screws at the end of the roofing panels to prevent winds from blowing off your roof.
You’ll require five panel screws and a lap screw in every screw line for panels at the end of the roof. However, panels at the center only require three panel screws and one lap screw.
Lap screws go in the rib ad are special screws. So, make sure you get the right ones. In addition, you must install a butyl tape seal, which is similar to mastic tape at the overlaps to hold the different roof sheets together.
What’s the Correct Screw Pattern and Spacing for 7.2 Panel/Western Rib?
7.2 Panel and Western Rib sheets are arguably the easiest to install. The panel screws go into the lows, and you need a screw in every low. Additionally, you need lap screws 12-18 inches on center and a butyl tape seal at the panel side lap.
Other Metal Roof Screw Spacing Considerations
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- What’s the Ideal Screw Line Spacing for Metal Roof on Solid Wood Substrate? Most jobs are often installed with screw lines at 24 inches on center. However, the general range is 18 inches to 36 inches. If you’re unsure, more attachments are always better.
- What’s the Ideal Screw Line Spacing for Metal Roof Over Purlins? Depending on the purlin spacing, your building engineer will determine the ideal screw line spacing over purlins. Generally, though, you may have screws on every purlin line or every other purline line depending on the purlin spacing.
- How do you Calculate the Number of Screws Needed for a Metal Roofing Project? Take the square footage of the roofing area and multiply the number by 80%. So, for a 1,000 square-foot roof, you need 800 screws. Alternatively, work with the knowledge that you need 80 screws for every 100 square-foot f roofing area.
Tips When Screwing a Metal Roof
Screwing down metal roofs is mostly a straightforward process, though you occasionally run into a few challenges. The following tips may come in handy;
Don’t Overtighten Screws
It’s a natural intuition to try and send the screws down as far as possible. However, beware that overtightening roofing screws comes with severe consequences.
For instance, overtightening can completely damage the washer, resulting in leaks. At the same time, don’t under tighten screws as it often leads to a weak roof.
Don’t Play the Angles
Trying to be smart with the roof installation project often leads to disaster. So, one of the things you should never attempt is playing the angles.
Slanted screws can damage the screws, causing leaking. Therefore, keep your screws straight and flush.
To Pre-Drill or Not?
Most screws used in installing metal roofs are self-drilling. Therefore, you don’t need to predrill the screw holes. However, pre-drilling may make sense in certain circumstances, such as installing the metal roof on a wooden substrate.
Pre-drilling is also worth considering if you suspect that the screws might tilt during installation.
Screws in the Ribs or Flats?
We mentioned this earlier. Both methods are acceptable., so it comes down to preferences and the type of project. Many people prefer rib installations because it’s easier.
Screwing on the ribs also significantly reduces the risk of roof leaks. However, there’s a greater risk of over-tightening and damaging the roof.
Meanwhile, screwing in the flats reduces the risk of damaging the roof from over-tightening – which is a big deal. However, there’s a greater risk of leaks as rainwater flows down the flats and over the screws.
So a small mistake will almost certainly result in roof leaks.
Metal Roof Screw Spacing FAQs
How Far Apart should Screws be on Metal Roof?
Screws on a metal roof should be one and a half to two feet apart to achieve a firm roof. This usually means a panel screw every three ribs and one lap screw at the end.
How should a Metal Roof be Screwed Down?
The best way to screw down a metal roof is with a hammer or nail gun in the trough. Keep the nails straight and flush (avoid slanting), and don’t over-tighten.
How Many Screws for Metal Roofing?
A simple formula to calculate the number of nails you need to screw down a metal roof is 80% x the square footage of the roof. For instance, if you have a 500 square-foot roof, you need 80% x 500 = 400 screws.
Where do the Screws go in a Corrugated Roof?
Most manufacturers recommend installing screws in the troughs of a corrugated roof for maximum hold. However, you can also install the screws on the ribs if you’re worried about the risk of leaks.
What is the Screw Pattern on a Metal Roof?
Panel screws are installed every three ribs, and lap screws 18 to 24 inches on the center for a standard 37-inch wide roof. However, for 39-inch wide roofs, leave four ribs between the third and last screw.
Summary
You should place metal roof screws one and a half to two feet apart (18 to 24 inches) during installation, though you can also place them 12 inches apart.
This usually means a screw in every third corrugation. Additionally, you need a lap screw on every side of the side lap. So, this means four panel screws and a lap screw for standard ⅞-inch (37-inch wide) roofs. Have any questions? We’d like to help.