Leaking slate roof box gutters, valleys and chimneys

There can be a multitude of reasons why slate roofs look fine but still have consistent leaks that just cant seem to be found and stopped. One problem that we see that is often missed, is some part of the metal flashings failing.

• Valley gutters or irons
• Soaker steps against abutments such as walls and chimney sides
• Chimney trays at the rear upper area of chimneys
• Box gutters – technically on slate roofs these gutters are more likely to be tapering center and parapet gutters.

Valley gutters or irons on slate roofs

Valley irons on slate roofs are often old and original and can have small pinholes in a number of places. Usually these holes are from rusting from the top or even from the underside. The holes can sometimes be obvious but sometimes they are almost invisible to the eye. They all leak – even the very small pinhole leaks usually show as damp patches or mold on the ceiling. As time goes on and the holes become larger, the leak usually shows as actual water running down walls or dripping through the ceiling.

Leaking soaker flashings on slate roof chimneys

Where a wall rises above a  roof slate or a chimney comes through, there’s nearly always hidden soaker step flashings. They are installed under the slates and turn up the wall to form a water tight joint. Because of the way they’re installed they tend to catch and hold a little dirt or other debris. As with other flashings these soakers do rust out. The trapped debris can remain damp under some conditions and it can accelerate the rusting out process. Although difficult to get a really good look at these soakers without removing slates, if you have leaks around your chimney area, it pays to really inspect them closely.

Slate roof chimney gutters or trays.

Another flashing that’s also capable of causing some difficult to detect leaks is the chimney tray at the rear of your chimneys. These also can appear to be OK, but they are also often full of pinholes that can be hard to see. A good test here is to get a screw driver or something similar and gently push it into the crease where it turns up the bricks. If it’s at all on its way out the driver will easily push a hole through it. If this happens you can be sure the gutter was pin holed and on the way out. Needless to say you better be ready to replace the gutter or at least temporarily repair it until it can be replaced.

Tapering center gutters and tapering parapet wall gutters on slated roofs

Many slate roofs old and new have center and parapet wall gutters. These gutters can be anywhere on the roof and unlike valley, chimney and soaker gutters are usually low pitched – just a little fall to allow the water to drain away. Areas on these older gutters that need close inspection are low spots where water can sit –  sometimes with leaf mold or other debris. As with the other gutters, close inspection of these gutters particularly at rusty looking spots will sometimes reveal small holes causing leaks.  Another aspect of these gutters that may cause leaks are the joints where the individual lengths are joined together. Sometimes, and it can be difficult to detect, the rivets give a little and the solder cracks or the silicone seal breaks and allows water through.

So does your slate roof look good but have leaking gutters 

To repair these gutters and stop the leaks really depends on what’s causing the leaks. Perhaps, for whatever reason, you only want the repair to last short term. If it’s slight rust pinholes you can sometimes repair the damage for a few years with silicon but in our experience, long term, you’ll eventually need to renew the gutter. Depending on how bad the metal has deteriorated and where it is on the gutter, a metal patch with silicon and rivets will last for a while – you don’t want to block the water flow in any way with a patch. If it’s a center or parapet gutter join that’s opened up, it’s sometimes easy to drill the existing rivets out, clean the join up, and reseal and rivet to make it water tight again.

So if  the slates on your roof appear sound and in good order , pay some close attention to the metal flashings, they can often turn out to be the culprit causing hard to find leaks.