How to fix roof leak?

Question

Hi everyone

We recently had a huge amount of rain in Perth and I’ve noticed a leak coming through the roof. I’ve managed to narrow it down to a gap where the aircon unit sits on the roof tiles. There is a small lip on the edge of the base plate, but I’m guessing it’s not enough to handle heavy downpours. Would someone with a bit of knowledge be able to point me in the right direction on how to properly seal or block this off? I’m thinking some flashing and flashing tape might do the trick, but keen to hear what the best fix would be.

Thanks in advance 👍

Nailbag · Answer

Hi @Taylorpwa

My strong advice is to get a roofing plumber in to sort the flashing as it won'y be that expensive to have fixed correctly. Though not that complicated, it can be for a novice. Water ingress at any level should be taken very seriously due to the potential for a small amount to be very damaging and costly.

Nailbag

Dave-1 · Answer

Good Evening @Taylorpwa

Pretty much the same answer as @EricL  :) I would make sure that the high side of the air con unit is free from debris (leaves ect) but the sides defiently need to funnel the water as EricL have shown.

Dave

EricL · Answer

Hello @Taylorpwa

Thanks for sharing the photos of your roof leak. It’s quite clear that the overflow is occurring at the cut section of the roof tiles, and there doesn’t appear to be any overflow guide beneath that area. In heavy downpours, water is likely running off the cut edge, spreading sideways, and finding its way into the roof cavity rather than being directed safely away.

A short-term option would be to install an aluminium flashing tape, such as

https://www.bunnings.com.au/fix-it-fast-repair-tape-150mm-x-5m-aluminium-waterproof-flashing-tape_p0592332

, positioned as far back as possible under the cut tile section. This can help form a barrier that catches and redirects water outward instead of allowing it to enter the open side channel. For best results, the tile surface should be cleaned thoroughly with a stiff brush before application so the tape adheres properly. The flashing should run well back under the tiles and extend forward to the edge of the metal skirting near the air conditioning unit, ensuring any overflow is guided away.

That said, this type of repair is only a temporary measure. Given the way the water is behaving, the more reliable solution would be to have a roofing professional assess and modify the drainage detail properly. A qualified roofer can install a purpose-built flashing or redesign that section so water is controlled even during heavy rain. This not only provides a longer-lasting fix but also ensures the work is compliant, warrantied, and better aligned with insurance requirements.

In the interest of health and safety, please take all necessary safety precautions when working at height. This includes using a safety harness and the use of scaffolding if necessary.

Let me call on our experienced members @Nailbag and @Dave-1 for their recommendations.

If you need further assistance, please let us know.

Eric