Leaking tiled bay window

[Giles Mann]

In the 18 months that we have lived in our flat, we have had some visible damp on our ceiling adjacent to the bay window (3 separate times altogether). It seems to happen after particularly heavy rain when it is also windy. The photo shows the alignment where the damp patch is occurring. The second photo shows the most extensive damp patch we have seen. It seems to start right next to window and spread from there.

Looking at the roof there doesn't seem to be any missing tiles. Also, the gutter doesn't overflow and is overhangs the top of the window by quite a lot. I'm wondering whether it's one of the following reasons:
- No proper lead flashing; there appears to be a mortar joint instead of this
- Perhaps combined with no cavity tray; 120 year old house so not sure if they had them (or an equivalent) back then
- Rain getting blown up and over tiles (I don't think there would be felt under there)

It's tricky to get access up to the roof because there is a conservatory below half of the bay window so I'm not really sure what my best course of action is. Any advice would be appreciated.

 

[^woody^]

As it's a flat, who is responsible for maintaining the structure and exterior?

 

[KenGMac]

Notwithstanding "woody" above,

Your roof tiles have a mild Moss Infestation over the entire roof, moss can and does allow rain water to get past the tiles. /// No felt??? ///

There is a small area of missing pointing between the wall and the cement? flashing [near the right hand side]

It appears that historically some tiles have been replaced?

Ken.

 

[Giles Mann]

It is a share of freehold flat so the owners collectively look after the maintenance.

Out of interest how does the moss let the water in?

 

[KenGMac]

Out of interest how does the moss let the water in?

OK what happens is that the moss has roots, the root system get in between the tiles, the moss grows on the tile joints.

When it rains, rain water is held back by the surface moss, and then the rain can pool or pond on the up-slope of the tile, following that the rain water follows the line of the moss roots into the property.

Given you have roof tiles, not Interlocking tiles it is easier for the water to ast as above?

Ken.

 

[HERTS P&D]

There is a small area of missing pointing between the wall and the cement? flashing [near the right hand side]

What he said.

Andy

 

[catlad]

No traditional lead flashing and a solid brick wall!
I would start with storm dry first.

 

[Giles Mann]

OK what happens is that the moss has roots, the root system get in between the tiles, the moss grows on the tile joints.

When it rains, rain water is held back by the surface moss, and then the rain can pool or pond on the up-slope of the tile, following that the rain water follows the line of the moss roots into the property.

Ken.

Thanks all for your suggestions.

Ken, that is interesting that the moss roots are extensive enough to do this.

I'll look at getting the moss cleared and a proper flashing installed. Obviously, it is a bit of a concern that the timber frame of the bay roof could be rotting.

 

[^woody^]

I doubt its the moss on clay tiles. The mortar fillet may have cracked