Remedy for Damp Patch on Ceiling

[stem]

Nine years ago we had an extension built, at the time I was concerned about the layout of the guttering and downpipes. Basically one side of the main house roof discharges onto a GRP gully on the extension roof. When it rains heavily a torrent runs down it. Here's a sketch of the layout.

Roof

• stem
• 22 Jul 2015

As the years went by and the odd storm / flash flood without incident, I stopped worrying. Yesterday, Mrs Stem noticed a damp patch on the ceiling below the gully whilst fly swatting. A quick inspection in the loft showed that the timber supporting the gully was now dry, but watermarked. There is no obvious damage to the gully, or the roof, and a white membrane is installed under them all. We don't know how long the stain has been there, because it's in a utility room and we don't generally look up when we are in there, but I'm not aware of any unusually heavy rain recently.

So, my questions are: Is the design of the guttering and downpipes OK, or should it be redesigned? If do how? Could this be a once in a lifetime (or 9 year) event due to a specific combination of weather circumstances? Is there anything that I should check?

 

[Crystalclear]

Hey Stem.

Random thoughts going through my mind, but if it was my house, I'd extend the down pipe from the house roof, run it along the GRP Valley (leaving a clearance for debris) and continue the extension down and along the garage gutter down pipe.

Technically you'll have reduced the burden on the garage gutter by 50%.

It'll be cheaper and quicker, than you having the valley modified to accommodate heavy rain days.

 

[^woody^]

It's a standard arrangement to discharge onto another roof. The fact that it does discharge there makes no difference to the waterproofness of the roof - the roof should be waterproof regardless of the amount of water.

You need to find out what is wrong with the roof or valley and rectify it, rather than try and divert the water.

Putting downpipes in valleys is certainly not standard practice.

 

[stem]

Thanks Guys.

Crystalclear, I did think about running the downpipe down the gully, but I wouldn't be able to fix it down, and I think the space left around it would catch leaves and prevent the water draining from the garage roof.

Woody, thanks for the reassurance that it's normal practice to discharge water from one roof to another albeit a lot of water, but it has been OK for 9 years. I've been on the roof today, but I can't see any visible problem. The valley is clear of obstructions, there isn't any visible damage and all of the tiles are in place. The cut edges of the tiles have been filled with cement, which is a bit cracked, but it has been like that pretty much from day one, but it's all in place. So I think I need professional assistance.

I called three local roofing firms listed on National Federation of Roofing Contractors (NFRC) website but no one can even come and have a look before 6 weeks! Never mind effect a repair.

 

[Crystalclear]

...I wouldn't be able to fix it down, and I think the space left around it would catch leaves and prevent the water draining from the garage roof.

I understand your worry, and you want it to be secure.

Just a thought though....I'm visualising Hedgehog Gutter Guard Leaf Filter placed in the GRP Valley, with the pipe sitting Ontop of it, and glued/pushed onto the end of the House Roof Down pipe, and glued/pushed onto it's own downpipe that would be screwed into the garage wall as normal. I don't see it moving with heavy winds to be honest.

You'll be better off taking a look from the inside; you'll see damp wood, and streakers where drips of water previously collected over the years.

For the record, stay wise about the "....ooooooh! We're busy for weeks!" Reply; they just want you to push them into coming over, so you pay what they ask for, in most cases, hiked up prices! :/