As winter looms (or if you are in the northwest, has already arrived), many people start thinking about what another season of ice and snow is going to do to their roof. If the roof in question is made of metal (also known as corrugated roofing, ribbed roofing, tin roofing, steel roofing), the choice of fastener is critical to ensuring the roof’s integrity. Sometimes a roof just needs to be refinished with new fasteners in order to be watertight, sometimes the entire roof needs to be replaced.
Either way, its important to use a good metal roofing screw to secure the metal roofing, whether new or existing, firmly to the underlayment. Underlayment can be either purlins (strips of wood running across the roof horizontally just for screwing into) or OSB/plywood sheets. If OSB is used, a #10 roofing screw typically does not meet the applicable home building codes in most states.
Jake Sales carries metal roofing screws in three main sizes, #10, #12, and #14. Each of the sizes has an EPDM washer that will last and stand up to hard use far better than the cheaper neoprene washers frequently found on lower end metal roofing screws. #10 screws have a 1/2 inch washer, #12 screws have a 5/8 washer, and #14 screws have a .55 inch washer.
Each size of metal roofing screw has its own particular usage case, although they overlap in many situations and can frequently be used interchangeably (but generally not on the same roof as using a mixture of screw sizes on a roof can be mildly aesthetically jarring). Although there are other sizes of metal roofing screws, such as #9, they do not meet the applicable building code in most situations.
With regard to sizes, for metal roofing screws, the larger the number, the larger/thicker the diameter of the screw.
Why are only the heads painted?
The best metal roofing screws only have a painted head with bottom of the washer remaining unpainted. This can slightly increase their cost as the screw cannot simply be thrown into a vat of paint, but must be put into a machine that carefully paints only the head and keeps the body free of paint.
Why is this important? Because paint on the body of a screw can prevent the screw from sealing itself tightly into the hole, allowing moisture to drop down through the roof around the screw body, resulting in possible damage to the underlayment and water getting into the attic. The wood will also wear around the screw as water repeatedly seeps through it, resulting in reduced strength and possible rot around the screw body. Additionally, painted screw threads do not correctly bind to the wood, allowing for the possibility of the screw “backing” itself out of the hole.
Why would you use #10, #12, or #14?
First of all, the #10 is primarily used when putting metal roofing down over purlins. Although in the past many buildings used #10 screws into OSB, today this is generally not up to code in most states. When building a new house or rebuilding an existing roof from the rafters up (new underlayment/purlins, new tarpaper etc) the most common size of roofing screw to bind the metal roofing to the underlayment is the #12 or larger. Galvanized to protect against corrosion, they typically last decades under normal wear and tear.
Jake Sales also carries a slightly different variant of the #10 roofing screw, one with a Mini Driller point. Although the standard metal roofing screw point does an excellent job of binding metal to wood, even without a hole being pre-drilled, some contractors like to use a metal roofing screw with slightly different point that has less of a need to have a pre-drilled hole in the metal. However, generally you are going to want to pre-drill all screw holes to ensure that the lines of screws line up neatly and straight across the roof. This is done by stacking the roofing on the ground and drilling the screw holes through every sheet at once.
If you are using screws to attach OSB to the rafters/trusses in preparation for metal roofing, do not use any type of metal roofing screws. Instead look to use a BTX type of screw/fastener. Metal roofing screws are designed to hold metal to wood, using them to hold wood to wood is not a recommended use and can result in roofing problems, including bulges in the roof where the screw heads are preventing the metal from lying down flat against the underlayment.
Another usage case for metal roofing screws is when a roof is being redone. Sometimes a metal roof is in need of refastening, not replacing. Older screws may have weakened and started to corrode, allowing water to seep in around the holes and get into the house. Older screws can also begin to back out of their holes, making the roofing vulnerable to wind.
Weakened fasteners can also allow wind to get under the metal on a roof, potentially leading to not only increased wear and tear on the screw and the hole as it is tugged around by the wind, but in some cases entire pieces of the metal roof are pulled apart from the adjacent piece. If too many screws are weakened or pulling out, roofing can even be blown entirely off the roof or folded in half around the remaining fasteners.
Frequently these cases can be corrected by simply redoing the fasteners. By replacing each existing screw with a new, slightly larger screw, the roof can be restored back to its original water tightness. Sometimes called a “ReGrip” screw, typically this means using a #12 metal roofing screw in the original #10 hole. Work your way from screw to screw, methodically replacing each one. Do not remove a lot of screws at once, work your way across a few at a time, making sure that each piece of metal roof is fastened back down where it belongs.
As you are installing metal roofing screws, whether you are re-doing a roof or putting an entirely new one up, here are some things to keep in mind.
- Don’t cram the washer down too much or too little. If a roofing screw is overtightened, it risks breaking
the seal around the washer and allows water to get in around it. If the screw isn’t tightened down enough, there will not be a seal around the washer at all, and water will seep down around it. Only tighten the screw down to where the washer snugly sits against the roof. - If the building is in a hurricane area, whether its a re-roof or a new roof, keep in mind that although #10 metal roofing screws usually meet all applicable code requirements if they are screwed into purlins, #12 and #14 metal roofing screws are far superior for roofs that will experience high winds. Of course no size of screw will protect a roof if a hurricane hits it full force, but #12 and #14 screws will do a far better job and last far longer against high winds than a #10 metal roofing screw will.
- If a new roof is being installed, stack the metal roofing on top of itself and pre-drill all of the screw holes to ensure that each row of screws lines up neatly all across the roof.
- On average, each hundred square feet of roof requires about 80 metal roofing screws.
That pretty much wraps up the general overview of metal roofing screws and their uses. If there is a question that you have that was not answered, please email us at tom@jakesales.com for an answer.