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Preventing leaks from screws in the roof

May 25, 2024May 25, 2024

Grayson's Gutter Guard

Could screws in your roof leak and cause water damage to your house? The answer is, of course, a resounding ‘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 during gutter guard installations.

At our office, we regularly test new products. These product tests include pressure testing of the screws used when installing gutter guards.

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:

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 a gutter guard installation

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 such as electrical wiring or other sheets.

Metal composite

It's very important to know 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 screw’s 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.

Safe places for roof screws

Never do the following:

What is a ‘watertight 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 install guttering and metal roof sheeting.

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

Pressure test conducted at Grayson's Head Office

In the photos below, you'll see three different types of gutter guard screws at the bottom of three 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. Each can above has one screw at the bottom.

8 Gauge stitcher screw starts to leak and has already dropped to 80mm in water height. The other two cans still contain the full 100mm 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 has 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 screw had finally dropped down to 29mm and the dripping was at an absolute standstill (no more dripping occurred once the water level was at 29mm).


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. 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 can maintain the integrity of your roof.

Image: Gutter guard installed to a valley with the screws bolted to the roof ribs

Type of screwSize & lengthMetal compositeWhat does Class 3 or Class 4 mean?Safe places for roof screwsNever do the following:What is a ‘watertight screw?’Plumbers’ advicePressure test conducted at Grayson's Head Office10 Gauge stitcher screw8 Gauge self drilling screws8 Gauge stitcher screwConclusion