leaking below dormer

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our house was renovated 6 years ago and a dormer added with a grp roof and zinc sides.

the dormer roof discharges water through 2 outlets (A,B in attached plan.png) onto different parts of the pitched fibre-cement roof. most of the water discharges directly beside the dormer on one side (A) which has lead soakers.

over the years we've found that when there is a lot of rain and wind water will leak through to the living room ceiling (C).

with the recent storm barra we've had few litres of water leak through again and have a roofersscheduled to take a look.

i was hoping you guys might have some independent advice on the best approach to get to rootcause and resolve the problem.

i was planning on asking the roofer to lift all the tiles along the dormer abutment to help identify the leak source. does that make sense?

thank you for your advice,

colm
plan.PNG IMG_20150219_152702.jpg IMG_20150303_150216.jpg IMG_20180405_185443.jpg
 

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I assume a lead soaker was fitted to each slate?
 
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I assume a lead soaker was fitted to each slate?
You would hope so. I can't help thinking that the pitched roof material should have been fitted and flashed against the dormer prior to the vertical weathering of the dormer cheeks.

Anyhoo, it looks like there is a vulnerable spot at the top of the abutment, right where there is a confluence of dormer cheek, hip and cement slate.
 
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I suspect its one of those designed in errors! not having a gutter at the front.
 
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Yes, soakers can just be seen in spite of the build-up of debris, much of it will be coming down with the flat roof discharge water - why the designer choose to slope & drain the flat roof that way is difficult to understand?
Why not slope to the front and then drop a down pipe?

Its also difficult to see what kind of drainage outlet has been use eg a chute maybe?
As noticed by others, that junction is suspicious - I think a large lead saddle might have worked better with the outlet discharging above it?
 
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Yes, soakers can just be seen in spite of the build-up of debris, much of it will be coming down with the flat roof discharge water - why the designer choose to slope & drain the flat roof that way is difficult to understand?
Why not slope to the front and then drop a down pipe?

our architect designed it this way unfortunately for us. years later i was looking in a housebuilding book and found the attached page with a big x through our dormer design.

Its also difficult to see what kind of drainage outlet has been use eg a chute maybe?

attached is a picture of the dormer roof water outlet which is made up of grp, cement, slates with a lead soaker underneath i think.

what would be the best approach for finding the rootcause? lifting all the tiles along the dormer abutment?

also, looking at the pictures one thing i noticed was that the pitched roof membrane was unsupported at the bottom. could water running down the membrane pool just before the lower grp roof and eventually leak? note that this area is close to where we see ceiling leaks inside the house. should the bottom of the membrane be supported in some way so that it will drain onto the lower flat roof?

thanks for you help!
 

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Thanks for the new pics.
No, dont go lifting the abutment tiles except as a last resort.

The lower membrane looks OK but the flat has suspicious water ponding staining? Is the flat possibly sloping towards the dormer?
Just because you see internal water damage at a particular point doesn't mean that the leak is there. But the more i look at the flat abutments with the pitch and the Dormer, & how the GRP has been installed, the more suspicious I become of what i'm looking at.
Then again I'm not on site so I could be well wrong?

Perhaps close investigating or even dismantling the outlet is the place to start looking? Check under where the edge capping stops..



Is the white covered diverting piece a mangled piece of zinc shaped from the edge capping?

Would diverting the outlet into a transition and then hang a drain pipe down the cheek of the dormer to discharge below? Maybe not - the outlet gap is the problem.



Perhaps you've already had a good look inside that area of the dormer? Boroscopes are useful for looking into walls and roofs - they can be hired or DIY'ed with a camera.
 
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firstly, note that 1-2 years ago when the leak happened again, i went out with a hose pipe and hosed each section of the roof for 30-60m.

i eventually got the leak to restart when i set the hose up on the dormer roof pointing out at the dormer grp outlet.

i thought that the concrete at the outlet might be the issue as it looked worn and also found one slate with a thin crack just below the lead soaker.

i applied tek/roof7 to the concrete and the cracked slate and could not recreate the leak with a hose afterward.

ive attached some pictures of the outlet before and after this. some are from a video so the quality isnt great. if the weather is ok tomorrow, ill get back up there to take some better pictures of the grp outlet in its current state.

i thought this might have done the trick until a few days ago when it started leaking again.

Perhaps close investigating or even dismantling the outlet is the place to start looking? Check under where the edge capping stops..

Would diverting the outlet into a transition and then hang a drain pipe down the cheek of the dormer to discharge below? Maybe not - the outlet gap is the problem.

yes, a drain pipe or maybe a gutter sounds like a good idea. what sort of transition would fit and work though? would it be possible to fit a hopper of some sort?

Perhaps you've already had a good look inside that area of the dormer? Boroscopes are useful for looking into walls and roofs - they can be hired or DIY'ed with a camera.

i have a cheapo boroscope and access to the pitched roof from the inside as there is an attic storage area in the eaves and there is no sign of water ingress.

the only place we can find water is in the ceiling cavity where the pitched roof meets the flat roof.

thanks again for your advice and insight
 

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i went up on the dormer roof and took a few more pictures.

the problem outlet is ~ 6 inches wide and concrete makes the flow take an immediate 90 degree turn down the rear pitched roof beside the dormer.

there is a wider outlet (12+ inches) on the far side of the dormer roof which hasnt given us trouble. on that side water flows onto the side pitched roof rather than turning 90degrees.

there isnt much debris over there though so i think the slope encourages water to use the problem outlet.

i guess the reason the builder did not do this on the problem outlet side as that there is a skylight closeby on that roof.
 

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With the new pics I'd say definitely take apart the problem outlet, remove the split slate & any slatework above it, and clean & dry the area both sides of the outlet. Then closely examine whats exposed looking for water trails.
The sand and cement barrier/diverter will might also have to be replaced for a fresh start?
 
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With the new pics I'd say definitely take apart the problem outlet, remove the split slate & any slatework above it, and clean & dry the area both sides of the outlet. Then closely examine whats exposed looking for water trails.

Thanks, that makes sense as a good starting point. Should the ridge tiles and cement also be removed do you think?

The sand and cement barrier/diverter will might also have to be replaced for a fresh start?

I don't mind a fresh start at all but I'm not sure what it could be replaced with.

Could more fibreglass be added on and used as a diverter or are there other options?
 
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We had a roofer out earlier looking at the outlet.

He was not keen on lifting slates to find evidence of a source for the leak.

He proposed covering the area around the outlet in aluminium flashing and using that this to route water down a new drain pipe which would run down the side of the dormer alongside the lead soakers.

Does this make sense? Would aluminium flashing or fibreglass make more sense for this purpose?
 
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