Can Screws in My Roof Cause Leaks?

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Pressure-Testing Gutter Guard Screws

Ever wondered if screws in your roof can leak and cause water damage to your house? The answer is of course “yes.” This is why caution should be exercised when placing screws or nails into any roof sections.

In this article we share with you some of the things to be aware of.

At our office, we regularly test new products. These product tests include pressure testing of the screws that are used in gutter guard installations.

The fact of the matter is, at some point you will always need roof bolts, screws or nails as part of any roof construction. Unless you’re able to use a complex series of mitre joints to hold your entire house together, these little metal fixing parts are always going to be mandatory.

The following factors should be considered when drilling screws into metal roof sheeting:

  • The type of screws used
  • Size and length of screw
  • The right (and wrong) places for roof screws
  • The type of steel (or other metal) in your screws
Standard Roof Screw 65mm long thread
A Standard Roof Screw has a 65mm long thread, with a hex head and rubber washer

Type of Screw

In corrugated roof sheeting, the standard roof screws that hold the sheets down is a 11 Gauge x 65mm Hex Head, often with a rubber neo washer, as seen in the above photo.

For gutter guard installs, we use short screws of no greater than 20mm in length. For angle trims that are fixed to your gutter edge, we use a 15mm long, 8 Gauge self drilling, Class 3 galvanised hex head screw.

The Stitcher screws seen in the photos are used for attaching saddles to the roof ribs. Nowadays, hex head screws are the most popular for gutter guards, as opposed to Philips head screws which have been proven to be too awkward for roof work.

Different Screws used in Gutter Guard installations
Different Screws used in Gutter Guard installations

Size & Length

Generally speaking, it’s safer to use a short length screw because you can be more certain there’s no risk of poking through underlying objects like electrical wiring or other sheets.

Metal Composite

It’s very important to be aware that the use of inappropriate metals can cause electrolysis and lead to severe rusting of your roof. For example, with copper gutters we only use our non-screwed Triple-G gutter guard. Some houses may have stainless steel gutters — in this case, we also recommend non-screwed plastic gutter guards. Our non-screwed gutter guards are great for roofs where screws are not suitable.

What does Class 3 or Class 4 mean?

The term “Class 3” or “Class 4” on the screws packaging refers to the amount of galvanised layering (rust protection) on the surface of the screw. Class 4 has more rust protection than Class 3 and is more suited to seaside applications where salt water is an issue.

Gutter Guard installed to a valley with the screws bolted to the roof ribs
Gutter Guard installed to a valley with the screws bolted to the roof ribs

Safe Places for roof screws

  • Placing watertight screws into the high point, or “rib tops” of roof sheeting is generally safe.
  • For gutter guard installations it is normally safe to use smallish screws to attach trims to the gutter edge. The most common screw used is a 15mm long, 8 Gauge Self Drilling screw that is Class 3 Galvanised. In the past, slightly longer 10 Gauge screws were also used.
  • If screws are watertight, it’s generally safe to drill to the tops of parapet wall capping. But avoid using long screws because they may press against the brickwork underneath and cause the metal capping to rise out of place. The 8 Gauge screws mentioned above are normally suitable.
  • The sidewalls of roof sections are generally a safe place for screws because there is no chance of water pooling.

Never do the following

  • Never drill screws into the pan floor of roofing sheets. The “pan floor” is the lower section of your roof sheet where the water flows to.
  • Never put screws into the framing of your solar panels (you might damage the panels and/or void your warranty). For bird proofing of solar panels, special clips are used.
  • Never drill screws into the fold line of roof valleys or the fold line of other roof pieces. If you must place a screw into valley metal, use minimal screws (only one) and ensure they are sealed.
  • Never drill screws into the floor of your gutters
  • Never drill screws into areas of roofing that are likely to pool water

What is a “water tight screw?”

The answer to this question obviously depends on the level of water tightness needed. Water is heavy — one litre of water weighs exactly one kilogram. As mentioned, you should never place roof screws in areas where there is a risk of water pooling. If water pools, there will be greater pressure and a greater risk of leakage. This is why you should never drill screws into the floors of gutters and the floor of roof sheets. High point areas of roofing, such as the peaks and sheeting rib tops, should not experience pooling and are only subject to rain splatter. If a roof screw is placed correctly, it should be impossible for rain splatter to penetrate the screw because the screw is completely filling its own hole.

Plumbers Advice

If in doubt, seek the advice of a licensed Plumber. For gutter guard installs, speak to an experienced installer. The Plumbing code states that all metal roofing is the domain of licensed Plumbers. Major renovations of metal roofing or installation of metal roofing and guttering must only be carried out by licensed Plumbers. Only Plumbers are allowed to be installing guttering and metal roof sheeting.

Gutter Guard Screws Testing
Gutter Guard screws being tested for water pressure at our Head Office. Each tin can has a different screw driven into the bottom and was filled with water to pressure test the screw seal.

Pressure Test Conducted at Grayson’s Head Office

In the photos below, you’ll see 3 different types of gutter guard screws in the bottom of 3 different tin cans.

Note that there is no rubber washer or silicone in place to reinforce the seal; all screws have been intentionally overtightened in this experiment to simulate what might happen if they were overtightened. We then turned the cans upside down and filled them with water. The height of the water level is exactly 100mm. The cans were left overnight to see whether the pressure of the water could breach the screw holes and leak down into the glass cups underneath. It should be noted that this is a laboratory-style test.

Gutter Guard screws can be seen in place for the pressure test.
Gutter Guard screws can be seen in place for the pressure test. Each can above has one screw in the bottom.
8 Gauge Stitcher Screw Starting to Leak
8 Gauge Stitcher Screw Starting to Leak and has already dropped to 80mm in water height. The other 2 cans still contain the full 100mm of water.

10 Gauge Stitcher Screw

The 10 Gauge Stitcher Screw was the best performer in this test. Less than 5mL of water actually leaked through the hole over the 24 hour period of the test. Considering the water pressure was 100mm and there is no sealant in place, this is an excellent result.

8 Gauge Self Drilling screws

The 8 Gauge Self Drilling Screws are used on angle trims and flat trims of parapet wall tops. This screw also proved to be an excellent performer, with approximately 5mL of water actually dripping through.

8 Gauge Stitcher screw after one hour of water pressure testing had dropped to 70mm depth.

8 Gauge Stitcher Screw

This screw was the poorest performer in the experiment. Over the first 2 hours of the test, the water steadily dripped through, but this dripping gradually decreased and came to almost a complete stop at 41mm in water depth. The cans were left for a total of 24 hours and during this period the glass receptacle had to be emptied as it was actually filling with water from above. At the 24 hour mark, the water level for the 8 Gauge Stitcher had finally dropped down to 29mm and the dripping was at an absolute stand still (no more dripping occurred once the water level was at 29mm).


The conclusion is that, under enough pressure, water can leak through almost anything, but if screws are placed in the correct position where water does not pool, there should be no leakage issues in roofing. With normal water drainage, water depth on your roof sheets should never be high, like in the above experiment example. Put simply, water should never pool for extended periods of time, on any part of your roof.

Roof screws are NOT leak proof, but water levels on your roof should never be high enough to be able to breach the seals. By using the right screws for the right job, you will maintain the integrity of your roof!

Call us on 1800 GUTTER if you have any enquiries about gutter guard.