Leak into cavity wall

[mordzy]

Hi All, I have a single story extension on the side of my house. The extension is constructed using a flat roof covered in that new rubber stuff. The existing house is constructed from block work and Yorkshire stone.

The extension is on the gable end of the house and is subject to a lot of driving rain.

When it rains, and we've had some heavy rain in the past month all is fine. When the wind is blowing rain onto the gable I have an issue where water is dripping down the cavity and into the building.

Ive used an endoscope camera to look up the cavity and can see a DPC membrane with water drips collecting on it where it drips down. It looks like its running onto it from the external side of the wall.

Ive had a builder/roofer look at it and he wants to blather the gable end is some sealer stuff. Im hesitant to do this as id prefer to know what the actual cause is. I dont think the entire gable of stone could be so easily porous... I dont have any issues above the DPC for example water coming down the cavity into the window in the story above. So I'm not sure its that the entire wall is porous as the builder believes.

He has told me the flashing for the flat roof is in the same course as the DPC membrane. Its my thoughts that this and the DPC shouldn't be in the same course as there wouldn't be much cement or that the water is able to track in very easily through this course then drip down.

Any advice would be really appreciated.

 

[Bonni]

It's ok for water to bead/drip down the cavity on the inside of the outer leaf. Cavity wall ties should have have a kink in them to stop water tracking across to the inner leaf. At openings (windows, doors etc..) and where extension joins, there should be a cavity tray fitted across the opening so any water that falls onto it, will leak out of weep vents or fall into the cavity away from the opening. The cavity tray is fitted into the inner leaf higher to the outer leaf.

The stuff the builder mentions is really just Thompsons Water Seal, ok for cavity walls but not solid walls. As long as the DPC (cavity tray) is lapped onto the flashing, that should be fine.

In conclusion, there's no such thing as a waterproof outer leaf wall. As long as it's in good state of repair with mortar between the bricks/stone, cavity trays and ties should be installed correctly. The cavity tray should run the full length of the extension and up to 300mm past at both sides, ideally with some weep vents approx 800mm centres. Thompsons Water Seal (or equivalent) may help, but it won't a cavity tray that's incorrectly fitted or compromised.

 

[mordzy]

Hello Bonni, thanks for the response. The tray you speak of is above this DPC that I can see by looking up the cavity. I dont know if the tray extends the full length of the extension.

To be honest ive had the same issue with some of the windows where water fills the DPC thats in the cement line under the lintle. It doesnt run back out through the weep holes which dont appear to be blocked. Ive experimented with a watering can on the lintle and within a few seconds can see water tracking in under the cement thats on the dpc.

The builder cant believe what hes seeing. All I can think is its coming in via the weep holes or the DPC is so close to the outer cement line that there's only a few mm of cement covering it and the water finds its way in really easily and tacking between the plastic DPC sheet and the cement.

Anyway. im not sure where to go, I didn't think the weather seal would give any decent solution.

 

[mordzy]

To clarify, I believe the 'tray' is black DPC that and can see. The flashing for the flat roof is cemented into the same course as this.

When it rains I don't have issues, when its windy and raining I get the leak.

Should the flashing be one course higher to prevent driving rain tracking in via this 'weak spot'

I will add some pictures.

 

[mordzy]

So you can see where the water appears. I can look up between the steels and see the DPC material. I will have to take a better picture of the flashing but you can see the edge of it in IMG_2846.jpeg.

 

[Bonni]

Your steel is not on correct padstones!!

It's a combination of -

1) There's no cavity tray
2) The cavity tray is not fitted correctly
3) The tray doesn't go full length
4) The cavity tray is compromised with holes
5) The inner side of the tray is not higher than the front where it's to weep out of

Unfortunately, a new tray needs fitted. And what a job that's gonna be.

 

[mordzy]

Whats wrong with the pad stones?

 

[Leofric]

Whats wrong with the pad stones?

There aren't any
Are there any approved architect's details for this roof to wall abutment situation and if so has it been built in accordance with the approved details

 

[mordzy]

Yes drawings have been done see attached. Building inspector has been. beams are sat on conc stones onto of the block work columns

 

[Leofric]

Drawing