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 is.
- 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 guarantee both options.
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 NO. I just don’t think that this can be done effectively. Weep holing has to be performed before the bedding sets. Then after the pointing is done, the weep holes have to be re-established through the fresh pointing.
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 us all about…[comment comment_file =”/comments.php”]