Common Causes of roof leaks

10 March 2023

Common causes of roof leaks

An unexplained indoor puddle is the last thing any homeowner, tenant or business owner wants to find on a Monday morning, but roof leaks are a fairly common occurrence in New Zealand buildings.

We’re all aware of the “leaky homes” crisis that plagued homeowners throughout the 1990s, but leaks can and do happen, even with well-built structures. In this blog, we’ll explore some of the common causes of roof leaks in New Zealand and share tips for identifying the source of a leak and what to do next. 

Let’s start with the most pressing question…

Why is my roof leaking?

Residential and commercial roof leaks can occur for a variety of reasons, but the most common are:

  • Faulty flashings
  • Failing membranes
  • Blocked gutters
  • Ageing materials
  • Cracked roof sheets
  • Inaccurate or loose fixings
  • Pooling water
  • Deteriorated skylights


Your roof is the first line of defence to keep your assets safe and dry, so at the earliest sign of a leak, it’s crucial to act quickly. If you’re trying to find the cause of a leak, one of these issues is most likely at fault. 

1. Blocked gutters

Your property's gutters are essential for draining water away and preventing damage. If they get blocked, you’ll soon start experiencing water ingress, with damp patches forming on external walls. And, as with any leak, the longer clogged gutters are left unresolved, the greater the damage can be.

Damaged or blocked gutters are usually fairly easy to diagnose. Check for signs of debris protruding from the sides and whether your downspouts are draining as they should during heavy rain. If you have a slow flow, there’s likely a blockage somewhere in the system. Ensure your gutters are cleaned annually, ideally before winter. 

2. Ageing materials

Even with regular maintenance, a roof may eventually age to the point of disrepair. Weather, moss, debris, and surface impact all wear down your roof, making it more brittle and likely to deteriorate. 

If you’re looking for a commercial roofing solution, repainting and surface rust mitigation can breathe new life into tired roofs. An alternative to a full roof replacement, it can extend your current materials by another 10-25 years. This is also a worthwhile option for residential homes with corrugated roofing.  

3. Faulty flashing

Flashings are an essential component of any metal or tile roof. Flashings are installed around the roof’s perimeter and around any penetrations, protecting them from water intrusion. Age-related wear-and-tear and exposure to temperature variations can lead to damaged flashing and significant problems.

Even recently installed flashing can be prone to leaks if installed incorrectly. In fact, as Christchurch roofers, we see flashing installation errors on a regular basis. Flashing issues can be difficult to diagnose, so if you suspect a leak, save yourself time and effort by calling in professionals.  

4. Cracked roof sheets

Although roofing materials are designed to be durable, they have a limit to how much they can withstand, especially after many years of exposure to the elements. 

It’s not difficult to spot cracked roof sheets. Just look for dents in the ribs of the roof sheets (most often in high traffic areas such as around HVAC plant). These dents will often develop a small crack in the centre. Be sure to address the issue quickly, as moisture can soon seep through the cracks, damaging structural timbers. 

5. Inaccurate fixings

Incorrectly drilled screws are another issue caused by shoddy workmanship and will inevitably lead to future leaks. If a fixing misses the purlins below, it can become loose and act as a direct path for water to enter your building. 

As you can imagine, finding a poorly drilled fixing from the roof’s surface is incredibly difficult. Instead, check the underside of the roof, looking for protruding nails or screws. Once identified, these fixings can be removed and the hole sealed to resolve the problem. 

Loose fixings will often cause a small leak which may go unnoticed. Over time, this can cause damage inside the ceiling or roof structure. 

6. Pooling water

Flat roofs are prone to leakage as they lack a pitched surface which would encourage water to drain away. In addition, flat roofs usually have seams that can unseal over time, creating weak points susceptible to water intrusion. Pooling water, therefore, presents a real threat to buildings with flat roofs. 

If your building has flat sections of roof surface, it’s important to regularly check them to determine if water is pooling. A roofer can help you determine whether pooling poses any risk to your building and, if so, what can be done to address the problem. 

7. Leaky vents

If not installed correctly, roof-mounted air vents can increase the potential for leaks, allowing water to enter the roof cavity through connection points. Additionally, airflow from the vents can carry moisture, dirt, and debris that settle on top of the roof, increasing the potential for corrosion and eventually leading to leaks. 

While most roof vents are installed so that leaks are prevented, older vents should be regularly inspected to ensure there are no hidden issues. This falls under the service of most scheduled roof maintenance services. 

Leaks from new vents are also common as the vents are likely to be installed by contractors with limited roofing knowledge. 

How do I find out what is causing my roof leak?

Identifying the source of a leak isn’t always a straightforward task. If you have high ceilings, an expansive roof or limited access, it’s best to bring in your local roofing company to diagnose the problem for you.

As Christchurch roofers, FHS Roofing works with businesses of all sizes, providing a range of services, including leak investigation and repair services

If you suspect a leak, contact us today to book an obligation-free consultation.

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