Hoping the buildhub hive mind can help on this one. ?

Our single storey wrap around extension was finished late last year but on taking heavy rain to the gable wall we’re ending up with damp patches in our new utility room. 
 

Flashing looks ok to my untrained eye but we do have a decent crack in the render above the utility room which could be culprit for water ingress.
 

The problem is after just having a plasterer out to quote for the render repair he didn’t think it was the crack and the leak was down to the flashing. 
 

The render needs repaired which I’m happy to do as it was an existing crack but I’m conscious if that doesn’t fix the issue what is my angle for going back to builder regarding him coming back to look at the flashing and making sure the issue is sorted. 
 

apologies for multiple posts but couldn’t get the pictures up in one go due to file sizes. 

What has been used to seal between the render and the top of the flashing on the wall? Can you grab a close-up?

External gable wall becomes internal wall in extension. Was a cavity tray installed above the flashing?

thanks for the quick replies gents and close up (just looks a bead of silicone has been run along where they chased the wall)  and wide photo attached.

 

Doesn't look like a tray has been installed if my understanding of them is right, the lead was just chased into the wall by the looks of it

What is the internal finish?  Plaster straight onto the old render or a battened cavity and plasterboard?

 

How quick does the damp appear after it rains? minutes? hours? or days?

It was plaster straight onto the old render no battens or plaster board.

As for how quickly it appears I’d say definitely within a hour or so and not days but it has to be an almighty lashing on the gable wall which unfortunately we haven’t had in a while.
 

Has taken me 2 months to even get a plasterer to come out and look at the job as the guy that plastered our extension is tied up for the foreseeable doing 14 apartments. 

Flashing is dog rough.
 

There are overlaps in it so you’ll need to get them sealed. I think the flashing is only cut into the render and not the wall behind so it will leak. 

I am not clear on how it would be possible to install a cavity tray in an existing wall, other than when the wall is opened up and a cavity tray is put in above the new steel.  Anyone?

You can buy retro fit cavity trays:

 

https://www.google.com/search?q=retrofit+cavity+trays+installation&oq=retro+fit+cavity+trays&aqs=chrome.2.69i57j0i10l2j0i10i22i30.9944j0j15&sourceid=chrome&ie=UTF-8#kpvalbx=_WuyKYP23FYCFhbIPpYaw0AU15

 

Beginning to think its a multitude of possible answers but water entering the render running down inside the wall and no cavity tray, will, for my money do it. 

Lead standards:

 

Lead sheet for lead flashing should be no longer than 1.5 metres. If the lead is cut any longer it could lead to splitting of the lead work due to expansion and contraction. When fitting flashings they should overlap by a minimum of 100mm. This is a good general rule of thumb on how to cut lead flashing, but there are conditions where you may consider increasing this overlap, such as prevailing high winds, driving weather, and exceptionally high flashings where the overlap may become vulnerable to water creep.

Thanks for all the replies, its very much appreciated.

 

If it’s the general consensus that a retrofit cavity wall tray is needed how to I approach this with the builder?

 

Is this a detail he should have picked up on or that the architect should have specified on the BC drawings?

 

Relationship is good with the builder and don’t want to get into a blame game just want an amicable solution for all parties to get the issue fixed. 

Difficult one.  Politely enquire with builder if one was put in. Check with architects details if one was specified. Check how the works were described. Be sure of your position first. Did the architect overlook specifying it? Did the builder miss it in the specification?

 

However, both should know that a cavity wall tray is always required in this situation.

 

Its usually part of my submission to building control (along with pad stones etc when required).

 

Good luck.

 

Marvin

 

 

Just checked the BC drawings and it clearly states “install proprietary cavity tray to existing cavity”

 

So looks like a conversation with the builder it is then. 

Sorry misunderstood the title ...

41 minutes ago, davidk said:

Just checked the BC drawings and it clearly states “install proprietary cavity tray to existing cavity”

 

So looks like a conversation with the builder it is then. 

 

Oh dear. Sorry about that. At least the wall hasn't been rendered yet. Looks like a few days work and very careful protection of the flat roof!

 

 

Edited April 29, 20215 yr by Marvin
spelling error

Flashing should work, it MUST be cut into the wall slightly uphill, overlaps need to be 150mm sealant, not silicone but lead mate 

I didn't see if they were high water absorption ("suckie " not in the dictionary how I mean it) soft bricks behind the render or not and I have seen problems in that situation before. But do feel if it was missed, it should be done. 

 

Typical info:

 

 

The wall is rendered above the roof so I'm not entirely convinced that the problem is a missing cavity tray. It might be but I would expect newish render to keep most if the water out of the cavity. 

 

 I would look at how the flashing has been done as per...

 

4 hours ago, PeterW said:

Flashing is dog rough.
 

There are overlaps in it so you’ll need to get them sealed. I think the flashing is only cut into the render and not the wall behind so it will leak. 

 

Perhaps wait until its all dry and take a hose up there. Play it on the flashing not the wall and see it damp spots appear.

@Temp thanks for this, I think I’ll give this a go before approaching the builder. 

I would get a hose up there running on the roof carefully to soak just the roof not the wall and leave it running for a few hours. Position it to try and soak the edge of the roof where it joins the wall.  This will rule out a roof problem, or identify a roof problem.