The subject of weep holes on tile roofs can get quite ‘touchy’
Weep holes or no weep holes?
This is a subject of much debate amongst roof tilers in Sydney (and the rest of Australia – it seems).
Why do we need weep holes?
Well, the picture on the left shows what happens when no weep holes are installed in the bedding along a ridge – and the bedding is cracked under the ridge.
Initially, the crack in the bedding under the capping will allow water to seep through and collect on the scalloped zone of the roof tile upstream of the bedding. When the bedding is firmly stuck to the roof tile and also if there are no weep holes, the ponded water grows in size as more water seeps in. Eventually, the pond overflows the top edge of the roof tile and into the roof cavity.
This usually takes a while to happen and that is why leaks at the ridge capping only happens during prolonged rainfall.
The combination of the two (cracking under the ridge cap and a watertight seal of the bedding to the top of the roof tile) can cause a roof leak under the capping.
It is important to note here that if you have one and not the other, there will be no roof leaks at the capping. This is why some painted roofs start to leak when they did not leak prior to painting. Prior to roof painting, the bedding may not be fully adhered to the roof tile and this allowed a seepage path for the built up water. Roof paints can be quite thick and will seal any cracks between the bedding and the roof tiles. Suddenly, both conditions are met and a leak appears…
In the past, the pointing work was done with an oxide coloured sand/cement mortar. Roofers back then knew that the pointing was quite like to crack under the ridge capping and let water in. That is why they were quite diligent in installing weep holes to prevent any leaks. Then Flexible pointing was introduced.
And because flexible pointing stuck to the ridge capping so well and did not crack (as much), roofers start to think that they could do away with weep holing all together. And they were mostly right. If there is no cracking of the pointing – then there will be no water build up and hence no need for any weep holes… So, the no weep hole (old fashioned) myth about flexible pointing started to spread.
But there is one thing wrong with this myth. It assumes that the flexible pointing will maintain its integrity and not crack. Unfortunately, there are some instances where flexible pointing will fail. The two most obvious are: excessive movement at the ridge capping/roof tiles, and application error by the roofer. This is why the flexible pointing manufacturers still insist that weep holes be installed through their material. It is a safety margin thing.
Are there any exceptions?
Well, of course there are:
- Terracotta roof tiles have a border system at the top of the tile that acts as a dam wall against any ponding that can build up. So, if a full tile is installed on the top row under the ridge capping, weep holes cannot be installed and they are not needed. However if a cut tile is on the top row, then weep holes are still needed.
- With the recent fashion of using flat profile concrete roof tiles, weep holing can be a bit of an option. This is because there are no scallops in the roof tile to collect the water. Any seepage will pool horizontally behind the bedding, run to the lap of the tile and dribble into the drainage course underneath. The drainage course acts as a alternative weep hole! But this doesn’t stop roofers from putting weep holes in anyway…
- When a ridge cap is repointed and the old bedding is quite sound and has no weep holes installed. This is a debatable case. Either the ridge capping is removed ( probably a more expensive exercise) or the ridge capping is repointed carefully (cheaper option). If the old bedding is sound – then there is very little likelihood of movement cracking in the new flexible pointing and if the pointing is put on carefully (with the right preparation), chances are that there will be no cracking of the flexible pointing. In this case, I leave the decision to the homeowner whether to weep hole or not. I will have a longer guarantee if new weep holes are installed and a shorter warranty with no weep holes.
Every now and then I am asked if weep holes can be drilled into the bedding when all the pointing has been done and set. The answer is MAYBE. I have experimented with the use of a long (300mm or longer) masonry drill bit (5mm diameter) and there is a reasonable success rate. In normal (low cement content) bedding, this will produce a weep hole along the top surface of the roof tile quite easily.
However, If high cement ratio bedding has been used, then there is going to be some destruction. Drilling will not work in this instance.
I also posted a blog on ridge cap repairs
I have a video there that goes through a roof leak that was caused by cracks under the ridge capping but no weep holes in the bedding. And what we did to fix it.
Check it out below if you want to see what weep holing is all about…
Addendum December 2019
There has been a lot of interest on weep holes for roof tiles and I am adding this bit of information to make more sense of this topic.
How to make weep holes:
I have always manufactured my own weep holers using ‘butchers hooks’. But rather than showing this manufacturing process, it is far better to show you what an integrated weep holer looks like and where to get one.
Hytile in Victoria manufactures a weep holer that you can purchase online. One of the prongs (the larger one) is used to make the hole in the bedding and the other is used after the pointing is done. The theory is that it is easier for a smaller prong to re-establish the weep hole through the hardened bedding – and it will smear a little bit of pointing into the circumference of the weep hole to better stabilise it.
Why no weep holes along the hips?
Weep holes are not normally needed under the ridge capping at the hips of the roof. Water that seeps in under the ridge capping starts to pool at the troughs of the roof tiles – but before they can overflow the top of the triangular cut, the water trickles over the adjacent downstream hump.
…. one of the wonders of gravity.
This keeps happening until the water finds a side lap on the roof tile. The water then runs into the lap and down the water course, making its way outside the bedding.
But gravity can only do its trick under normal roof conditions. When the roof gets too flat, water can overflow the cut edge before it has a chance of running down the hip to the tile lap. This is why tile roofs are no good if laid too flat.
Another abnormal condition happens when the original roof tiler cuts one of the hip tiles too short. This reduces the capacity of the cut roof tile to store water before it can trickle downstream. The resultant leak over the cut edge then happens.
Yet another abnormal condition exists when excessive (width) bedding is used. The excessive bedding also ‘eats up’ the storage capacity of the cut roof tile and results in very little resistance to overflowing leaks.
… And we all thought ridge capping was a simple job!
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