Why Your Roof Is Leaking.

Tiled roofs can leak at the most inopportune times (usually when it’s raining), and finding the leak can often be a very frustrating and irritating exercise. In this article, I’ll help you identify the reason for that pesky leak (and hopefully fix it); starting with the more common and gradually getting to the borderline bizarre. 

• Broken tile

This one is a no brainer. A broken tile = gap for rainwater to seep through. 

• Broken water course

The overlap where the tile sits side-by-side can break easily. Sometimes this will not be visible, as the bottom section breaks and the overlapping tile will conceal it. If this is the case, you may need to pull some tiles out to find it or check from the roof cavity. 

• Damaged mortar work

Cracks in the pointing can allow water ingress. Unfortunately, you’ll need the roof re-bedded and pointed. 

• Damaged lead around a flu

Lead can split over time or the seal between the lead and pipe can go. Either replace the flu flashing kit or put some silicone on it. 

• Damaged/rusty/blocked skylight/chimney/aircon flashing

These roof features have a flashing system around them that are prone to problems. Clear away the debris if possible, or if its rusting or damaged, you’ll need to have the flashing replaced. 

• Overflowing gutters

If your eave sheet is sitting on the top of the wall or window, then when the gutter overflows the water can easily find its way in – this is only possible when the leak is very close to an external wall. Drill some holes in the front of the gutter to allow the water a point of escape that is not onto your carpet. Be careful with this, as too much water near your foundations will cause uneven settling of your home. 

• No weep holes

On a cement tile roof at the top ridge line, the use of weep holes was common prior to the increased use of flexible pointing. The purpose of a weep hole was to let excess water drain from the gully section of the tile before it filled the gully and entered your home. If the leak is directly under the top ridge, it may be that – you’ll need to have the roof re-bedded and pointed. 

• Flexible pointing coming away from the concrete bedding

If the leak is under a hip or ridge and the pointing is coming away from the bedding, then this is also a common leak point. If a roof is over-pointed in flexible pointing without removing the old bedding (or the bedding is removed but a sandy mix is used), then the flexible pointing will expand and contract independently of the foundational cement and you will see a small gap at the junction between the pointing and the ridge cap. This small gap will allow water in and cause leaks – you’ll need to properly re-bed and point your roof. 

• Leaking on the lower floor section of a split-level home

Apart from the above, the two next most obvious reasons are the apron flashing (the sealing flashing that stops water coming in from the point that the upper storey wall meets the lower storey roof), and an upper storey down pipe that discharges onto the lower storey. The apron flashing normally requires replacement and the downpipe needs a spreader. If the downpipe has a spreader, then the spreader needs lead under it to help disperse the water. 

• Worn or blocked water channels

Older cement tiled roofs (usually 50+ years) can wear excessively in the overlap where the tiles sit side-by-side. There are two grooves in this overlap that are designed to channel the water down to the tiles below. When concrete tiles get old, these channels wear flat and allow water to enter the roof cavity.

Mossy roofs (particularly terracotta tiles) or roofs with excess debris can have the water channels block up, which doesn’t allow the water to drain out and instead diverts it into the house. Worn channels are irreparable and a new roof is required. Blocked water channels, however, can be fixed by pressure cleaning the tiled roof. Prepare to get some water in during the clean out and do not do this yourself, as a wet roof is very dangerous. 

• Low pitched roof slopes

If the angle of the roof is too low in comparison with the rafter length, then the tiles will be submerged with water in heavy rain. As a guide, with a 4m rafter length a tiled roof will need at least a 17-degree fall. For every extra metre of rafter length, two degrees should be added to the pitch.

So, if you had an 8m rafter length, your pitch should be 25 degrees. If this is borderline, you can have Sisalation installed under the tiles to act as a secondary roof membrane, but in most cases the answer is to replace the tiles with a Colorbond roof. 

• Debris on the roof or excessive lichen/moss growth

Heavy lichen growth can impede the flow of water and divert it into the home. The same thing can happen with roofs that have lots of leaves and foliage on them. Pressure cleaning the roof is the best solution here, but once again, do not try this yourself as a wet roof (particularly one with terracotta tiles) is extremely dangerous. 

• Debris trapped between tiles

On rare occasions, there can be rubbish trapped between tiles. I remember one occasion where a roof was leaking and no one could ascertain the problem. Turned out it was a small piece of wire that had become wedged between two tiles and was channelling water along its length and into the roof cavity – this can also occur with twigs and leaf debris. It is very difficult to find, but once you do it’s an easy fix. 

• Warped tiles

On rare occasions, a terracotta tiled roof can leak for no apparent reason. If this is occurring, it’s worthwhile to check how well the tiles are sitting on the battens. If warping has occurred (either during the initial firing of the tile or as a result of later expansion or contraction) then you may get water in during the right combination of wind and heavy rain. The only solution to this aside from replacing the roof is to install a sparking or Sisalation membrane under the tiles in the affected area. 

• Unsealed wall panels

If you have had a second storey added to your home and it has blue board walls or other panelled type cladding installed, water ingress can occur from the joins where the panels sit side-by-side. Check to see if the panels are properly sealed – if not, there is fibreglass tape available that can be applied to the join to weatherproof the walls again.