LEAKING GRP FLAT ROOF

[texas]

Hi i moved into a renovated property 6 years ago It is a terrace property with building both sides and higher than my flat roof.

 

The kitchen has a flat roof with 3 sky lights. One large one medium and a small one. 

 

The roof is a GRP roof. 

 

We moved in and after about a year there was a small leak through the roof of the kitchen. We called the roofer out who saw no issue with his roof and we called the skylight people who saw no issue with the skylight. 

 

The roofer re coated the roof and we hoped all was good. 

 

Over the next 2 years it leaked periodically. 

 

We asked third party people to come and inspect the property. They said all the work looks in great order. 

 

I instructed a heating specialist who essentially heated up my kitchen and did some thermal imagine to see where cool spots were internally and externally. Nothing was conclusive but he saw some cool air coming in from a neighbouring property. After inspecting the date the neighbour repaired the whole of his properties timber side. 

 

After a year or so it leaked again.

 

The leak every time comes in near or around the same corner of the sky light. 

 

We contacted the neighbouring property whose workman inspected his work and he said his work was still in perfect order. My roofer said the same about his work. 

 

The roof light people came again lifted up all roofs and saw no problem or evidence of water coming in. However there was no weathering ( the roof lights we have dont require them according to the company who make them but we had lead flashing fixed as the roofer was concerned all along this was the issue. 

 

After 4 mths its leaking again. 

 

It can rain non stop for 2 weeks and not leak and then another time it can rain lightly. there seems no correlation of wind or weather pattern etc to trigger the leak. 

 

Ive attached some photos. Does anyone have any advice? 

 

Many thanks in advance.

 

 

 

 

[texas]

[texas]

the leak enters the property below the red circle on the first pic. 

[texas]

sorry the leak enters into the kitchen below the purple circle in the first pic. Ie at the corner of the skylight

[Happy Valley]

Problem with GRP is that water can travel through the fibres of the CSM or chopped strand mat so where the leak is showing in the kitchen ceiling may not correlate with where it is getting in above. Is there a gelcoat finish on top of the roof? All gelcoats are permeable unless it is an epoxy based one so finding the leak could be difficult. 

 

It may be worth going up there with a moisture meter on a really dry day and check out the area concerned in an attempt to locate areas of increased moisture.  

Edited May 5, 2021 by Happy Valley

[texas]

Thank you for the speedy reply

 

I am not sure if it has a gel coat covering. The roofer is coming around tomorrow morning again i will ask. 

 

I appreciate the water can travel but we cant seem to work out where from or how. 

 

I forgot to add i had a guy cut a hole in the kitchen ceiling at the point of entry. So we could try and identify where the water was travelling from. Sadly there is some sort of layer of "warm roof construction" so the board i am seeing is not as detailed as i had hoped as the water could be travelling from somewhere else and then entering at the point of entry where it somehow reaches an obstacle or a low point. 

 

I am going to suggest perhaps we cut the next layer up from inside and remove the insulation to try to guage where the water first comes in. 

 

I will discuss with him the moisture meter you suggested. 

many thanks

 

 

[SteamyTea]

There are a number of reasons that it may be leaking, hard to tell from your picture.

So a number of questions.

Does the roof fall away from the wall/corner where you get the water marks inside?

Does it leak every time there is an good amount of rain, or only sometime?

What is above the wall, is the gutter in good condition?

As it is a kitchen below, is that causing condensation?

How is that pipe sealed to the roof?

What are all those circles in a line, bolts/screws?

[texas]

 

Does the roof fall away from the wall/corner where you get the water marks inside? ESSENTIALLY THE FLAT ROOF POOLS ON THE NEAR SIDE OF THE PICTURE. THERE IS LIMITED SLOPE BUT TO ANSWER YOUR QUESTION YES I THINK IT DOES.

Does it leak every time there is an good amount of rain, or only sometime? ONLY SOMETIME. I WAS CONFIDENT IT WAS WIND RELATED TO START WITH BUT IT CAN BE SUPER WINDY AND NO LEAK AND THEN VICE VERCA

What is above the wall, is the gutter in good condition? THE GUTTER LOOKS IN GOOD CONDITION TO ME. IVE INCLUDED A PIC BELOW

As it is a kitchen below, is that causing condensation? NO THERE IS NO CONDENSATION ON THE SKYLIGHT OR IN THE CONDITION

How is that pipe sealed to the roof? THE PIPE IS SEALED AS IN PICTURE BELOW

What are all those circles in a line, bolts/screws? I AM NOT SURE THE PICTURE I HAVE SHOWN WAS ON A COLD DAY I WILL INCLUDE ONE ON A NORMAL DAY BELOW> I WILL ASK MY ROOFER TOMORROW THOUGH.

 

Sorry for caps but felt the best way to respond to distinguish my response from your question

 

cheers

 

[texas]

[texas]

[markc]

Really dont envy you trying to find the source of your water ingress, so many possibilities - all those mentioned previously plus it could be getting in via the window/cill then down behind the render (presume that is a rendered patch) and under the roof material that way

[texas]

Hi MarkC when you say render do you mean the bit I’ve circled? 
 

ive never liked that part but every respective person that has gone up there dismisses that area as an issue. 
 

But I don’t like the look of it. 

[SteamyTea]

5 hours ago, texas said:

Does it leak every time there is an good amount of rain, or only sometime? ONLY SOMETIME. I WAS CONFIDENT IT WAS WIND RELATED TO START WITH BUT IT CAN BE SUPER WINDY AND NO LEAK AND THEN VICE VERCA

Highlight the text you want to reply to and a pop up will appear that says "Quote Selection".

 

Wind direction may be important.  If rain is hitting the wall and getting between the wall and the flashing, it may be getting in and then finding a path.

I had an ongoing leak in a downstairs window, took me two years to find out that it was cracked render 3 metres away.  It was the wind direction that gave the game away.  It only happened when a proper SW hoolie was a blowing.

[steveoelliott]

So... I went through a real conundrum with our flat roof made up of PVC and used as a terrace.

 

When we looked at the house, it had a leak and that was supposedly resolved by renewing the silicon between the up stand and wall (or so we thought). If the truth be known my gut told me the roof would cause us problems if we brought the house, but I chose to ignore it!!

 

The roof terrace is ~4m x 4m and has two parapet walls.

 

Around a month after moving in, following no real rain but a hard frost we had some damp / blown plaster over the top of the wall underneath one of the parapets, near to where the outlet is for the terrace. I got some folks round to look at the roof and remove all the slabs, pads, protective fleece etc. to inspect the roof and outlet. Everybody was convinced it wasn't the roof stating it looked in good condition and was a "good job". I was persuaded it must be the copings letting water in. So off they came, to be re-laid with a DPC underneath (apparently this had been neglected when built but there was nevertheless a cavity tray underneath")

 

Now... this seemingly fixed the problem for many months until it was getting warmer and we brought all the slabs back up to terrace. After the first bought of heavy rain we had two massive damp patches on the ceiling but nothing further on the wall this time.

 

I was now convinced it has to be the roof based on location and the amount of water. In the first instance I removed a group of slabs (around 7-8) near the corner of the outlet  to take a look but couldn't see anything... It rained long and hard for days and no further leaks; I was perplexed until I remembered I'd moved the slabs. I put them back and the leak returned the next day! I proved this theory several times by placing and removing them.

 

Once again... all slabs came off the roof and I had folks round to look at the roof. All again said it all looks to be fine but clearly accepted there must be an issue. They were puzzled by the removal of slabs stopping the leak and I don't think gave it much credence but I certainly wasn't lying. All of them offered to either do a complete renew or repair (the later would involve overlapping all seams etc.) I was so sick of it that I opted to renew the membrane completely and also replace the old copings with new ones.

 

When it came to doing the job... both parapet cavity's were bone dry before being replaced with new porcelain ones. When the roofer came he was almost laughing and joking saying there is nothing wrong with this roof it must have been the copings etc. etc. then he cut the membrane and saw a huge damp patch. As he cut further and stripped the deck he found the root cause; a bad weld where the membrane meets the up stand. He said this would never have been found without going through the stripping process. I can only suspect that the slabs must have exacerbated this condition further and led to a leak or at least enough water ingress to get through the ceiling.

 

So in short, from my layman's experience, flat roofs and parapets are a nightmare if not constructed and detailed impeccably. I will actively seek to avoid both flat roofs and parapets on any future house I purchase.

 

All of this probably doesn't assist you a great deal but I wanted to share my experience. My advice would be to not rule out anything and try to find a builder / roofer who is meticulous to assist in locating your leak.

 

Edited May 6, 2021 by steveoelliott

[texas]

15 hours ago, SteamyTea said:

Highlight the text you want to reply to and a pop up will appear that says "Quote Selection".

 

Wind direction may be important.  If rain is hitting the wall and getting between the wall and the flashing, it may be getting in and then finding a path.

I had an ongoing leak in a downstairs window, took me two years to find out that it was cracked render 3 metres away.  It was the wind direction that gave the game away.  It only happened when a proper SW hoolie was a blowing.

Hi thanks SteamyTea the guys are around again now. Ive asked them to look at the area you suggested

[texas]

Thanks SteveoElliot

 

Sounds a long process to find your leak. 

 

Hopefully ill get there with mine. 

 

Many thanks all of you 

 

[scottishjohn]

after all that work --my guess would be flashings or around any penetrations ,sky lights etc  and it is running  along roof timbers on inside to where it shows inside

It may be cheaper to drop the ceiling down -dry it out --then wait till it leaks again and track it ?

you could at least test with a hose on roof and see exactly where its coming in -providing you hose  one area of it at a time  and start from lowest point of roof and work back to highest 

can,t see it being the main area of grp if it has been recoated --got to be at and edge of it somewhere .

start by playing a hose on the skylight  to roof joint nearest where it comes in would be my first port of call,