Guide for identification of leaks on tiled roofs

A concrete tiled roof is among the most durable roofing systems available for pitched roofs, with a typical lifespan of up to 60 years. In addition to its longevity, a concrete tiled roof requires minimal maintenance and offers an aesthetically pleasing appearance.

However, leaks can still occur in these roofs. While it may be beyond the capabilities of the average homeowner to undertake roof repairs, sometimes the problem is simple and the fix is easy. If you’re uncertain, don’t hesitate to contact a recommended roofing contractor for professional advice and a quotation.

Here’s a guide to the common causes of roof leaks and suggested repair methods. Even if you choose not to undertake the repairs yourself, this guide will help you identify potential issues and ensure that a roofing contractor is performing the correct work at a fair price.

The Two Most Common Reasons for Leaks on Concrete Tiled Roofs

The most common causes of leaks in concrete tiled roofs are lack of maintenance and poor roof design.

Common Signs of Leaks

• Brown ring stains on ceiling boards
• Brown water mark stains on cornices
• Streaks and water stains on walls
• Sagging ceiling boards
• Flaking paint on ceiling boards
• Damp high up on walls, such as powdering and flaking paint
• Water exiting through light fittings without visible water damage elsewhere

Once you’ve identified signs of water damage or physical water ingress, consider these additional factors:

• Does the leak only occur during rain? Often, geysers are located in the ceiling space, so it’s essential to rule out plumbing problems.
• Does the roof leak every time it rains?
• Does it leak only when there is wind with the rain?
• Does the roof leak only when the rain comes from a particular direction?
• Does the roof leak only when the rain reaches a certain intensity or duration?
• Does the roof leak only during heavy hail?

These are important clues that can help an experienced professional determine the cause of the water ingress.

Locating the Leak

Once you’re certain that the roof is leaking, the next step is to establish the location. Measure the distance from wall to wall where the leak appears inside the house. Then, look out of the window and identify a landmark so that when you’re on the roof, you can pinpoint the exact area of the leak.

Common Causes of Leaks on Tiled Roofs (In Order of Probability)

1. Broken or cracked roof tiles
2. Misaligned or shifted tiles
3. Valleys or flashings blocked with debris or leaf litter
4. Defective waterproofing to flashings at parapets or around chimneys
5. Cracked roof ridges
6. Incorrectly applied waterproofing membrane over tiles, trapping water
7. Disintegrated or incorrectly installed plastic underlay
8. Roof paint applied too thickly, or attempts to ‘waterproof’ the roof with a liquid compound that glues the tiles together, trapping water

Investigating the Leak

Carefully ascend the roof, taking all necessary safety precautions. If the roof is too high or steep, it’s best to engage the services of a professional contractor.

Locate the approximate area of the leak using your predetermined measurements and landmarks, and carefully inspect the roof.

As a general rule, if the leak is in the middle of the ceiling, it’s likely due to broken or shifted tiles, leaking valleys, or cracked roof ridges. Water running down the wall or leaks at the cornices are more likely related to a flashing problem at parapets or around chimneys. However, these are just guidelines, as water can travel in unexpected ways!

If an obvious problem is found, repair it according to the suggestions below. If nothing is immediately apparent, further investigation may be required. Lifting a few tiles in the leak area may reveal water marks on the plastic underlay underneath. Additional tiles can be lifted to track the problem back to its source. There may be more than one issue, and all potential causes of leaks should be addressed.

Poor Roof Design Aspects

• Roof tiles running into an angled parapet
• Valleys and ridges in close parallel proximity
• Overly complicated and fancy roof designs that often lead to problems
• Roof pitch that is too flat
• Roof pitch that is too steep, causing tiles to slip and making access difficult
• Concealed box gutters
• Pitched roofs that join with flat roofs

Repairs Homeowners Can Undertake

Replacing Broken Tiles: Most concrete tiles are still available new. Builders’ merchants such as Buco and Leroy Merlin typically have stock, or you can contact manufacturers like Marley or BMI Group directly. Second-hand builders’ yards may also have tiles that are no longer in production. It’s wise to keep 10-15 spare tiles on hand for emergencies.

Realigning or Securing Misaligned Tiles: Tiles may slip if the roof is too steep or if the lugs that hook onto the wooden batten are broken. A common area for tile slippage is over metal flashings at parapets, skylights, and chimneys, as there is nothing for the tile to hook onto, so they simply obey gravity. To repair, apply an acrylic waterproofing membrane such as Aquagard Permaflex to seal the junction of the wall and roof tile, preventing future slippage and providing waterproofing.

Cleaning Valleys: The build-up of debris and leaf litter in metal flashings is a very common cause of roof leaks. During heavy rain, water gets blocked and can overflow the flashing edges. Leaks from this can be severe. To repair, gently push up the tiles and use a stick to scrape away the debris. A low-pressure hose can then flush away the remaining muck to ensure free water flow. A 50mm gap between the tiles is recommended, which can usually be achieved by pushing the tiles up slightly on both sides without cutting. Regular maintenance may be required, especially if there are trees nearby.

Roof Ridge Repairs: Loose cement on the ridges should be removed. Cracks and holes should be filled with a 2:1 sand-cement plaster mix, incorporating a bonding liquid such as Aquagard Mortabond into the mortar. An acrylic waterproofing compound like Aquagard Permaflex, combined with a 100mm wide polyester reinforcing membrane, can be applied to the defective joints.

Waterproofing Flashings: An under-tile flashing is a galvanised metal plate concealed under the tiles where they adjoin a parapet or chimney wall. The flashing has a lip underneath to prevent water from spilling over. The top edge is sealed with a metal counter flashing or a waterproofing bandage. Sometimes dirt collects in this flashing, causing water to overflow the lip and enter the building structure. Covering the flashing with a waterproofing membrane can effectively seal it off and prevent tiles from slipping. This can be done using Aquagard Permaflex waterproofing compound with a 250mm wide polyester reinforcing fabric. Though it may seem daunting for first-timers, with patience, cutting, and dressing, it can be done.

Repairs Best Undertaken by a Professional Contractor

• Installation of new plastic underlay sheeting
• Relining of valley flashings
• Reinstatement or replacement of hips and roof ridges
• Rectification of sagging roof structures
• Partial or complete roof replacement

Things You Should Never Do to Your Tiled Roof

• Seal joints between roof tiles with waterproofing membrane
• Apply thick, heavy-duty waterproof coatings to ‘seal’ the roof tiles
• Apply roof paint too thickly, clogging the grooves and overlaps of the tiles
• Paint your roof because you think it will ‘seal’ it—only paint your roof if you wish to change its appearance
• Apply cement or waterproofing in the valleys to ‘seal’ them