Help! Roof leaking on extention, velux window flashing foam

23 Dec 2019
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United Kingdom
Hi all,

Bear with me with my detailed post, but I thought more information is better than too little!
I've done a lot of researching on the net and a bit on this forum and i'm looking for some advice and also give you my opinions/findings too!

My parents have a fairly recent rear extention built (about 4 years ago), south facing, with a low pitch, tiled (redland 49 interlocking) roof, and a velux window.

I now feel the pitch was too low for tiles, but building control approved it and up until now there have been no issues.
Recently however with the windy heavy rain there was a leak in the kitchen extention with water dripping through one of the spotlights below the velux (around 1 drip every 20 sec).

We've had windy, stormy rain in the past so I couldn't see why it's leaking now (there isn't any cracked or missing tiles.

Over the weekend while it wasn't raining I decided investigate further, popping my head through the velux and also going on to the roof.

Looking along the side flashing channel, there seems to be a bit of a gap above the channel ridge and the side profile of the tiles (so if there was strong cross wind, the rain could get through these gaps (if that makes sense).

I pulled the bottom 2 rows of tiles that run up along the side of the velux flashing (on both sides) and noticed on one side the membrane was quite damp beneath the bottom corner of the velux (the other side seemed ok). This seemed to match with the drip coming through the same side of the spotlight
The foam trim that runs along the 2nd channel of the velux flushing had totally disintergrated into a mess (on both sides), and it seems like under heavy rain (especially when windy), the rain got through the gaps on above the first rain channel ridge & tiles and into the 2nd channel.

As there wasn't any foam left, the water stream breached the 2nd gutter channel onto the membrane.
The flashing kit looks like the EDZ:

And as you can see around the 2:35 mark, the the corners of the flashing have to be folded over like a triangle - probably to channel the water onto the tiles - HOWEVER, the bottom corners of my flashing were not folded, so I suspect that the water just ran off the sides onto the membrane.

I believe the EDZ flashing kit has now been superceded by the EDW:

And as you can see the bottom flashing design is modified with a triangular ends and a lip - I would guess so the water doesn't run off the sides!

I have now folded the corners like instructed in the video, so I'll see what the results will be!

I would need to replace the foam strip that runs along the 2nd gully of the flashing (under the tile) - Any idea where I can get the foam only from?

Finally, i've also noticed at the top of the velux window, the row of tiles are very close to the velux window and cover most of the top drainage gully (probably 10mm gap)- after reading a bit online and watching the velux installation videos, a minimum gap of 60mm should have been left!!!

I think I should be able to push back the row of tiles that run along the top of the velux back to expose the required gap (i'll have to use an angle grinder to cut out a corner piece where I can't push the tile back).
My other quest is, what happends when there isn't the recommend gap above the top of the velux and the tiles?
I can't seem to work out what the negative effect would be and if it has contributed to the leak

Thanks and apologies again for the long-winded post, but hopefully I also may have helped others with what I uncovered!
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The foam is attached to side flashing trims. This is then trimmed to the under profile of the tile. Get a new kit and refit it yourself. its not rocket science
The foam is attached to side flashing trims. This is then trimmed to the under profile of the tile. Get a new kit and refit it yourself. its not rocket science

Thaks for the reply.

I've had another look this morning, that the foam from the central hinge pivot towards the top end of the side flashing channel looks ok, but from the central pivot down to the bottom - disintegrated!

Do I have to buy a whole new flashing kit or can I purchase just the foam? (I guess it should work out much cheaper for just the foam).

I've found this:

Will this be suitable?

What are your opinions on the difference between the EDZ and EDW bottom flash apron (ie the shape of the ends)? Do you think I should replace the EDZ bottom flashing piece with the EDW version as it looks like it funnels the water away from the sides and down onto the bottom row of tiles?

I've also pushed up the top row of tiles above the top of the velux to leave approx 10cm gap -previously it was approx 2cm (60-150mm is instructed).

THanks for your help!
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call them on 01592 77225 tell them what you want.. we have ordered individual flashing/trim pieces in the past but not just the foam
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Merry Christmas everyone!

I took the opportunity earlier today before Christmas lunch to lift off a number of tiles to have another look.

I noticed that due to the low pitch of the roof, heavy rain water builds up a little at the bottom flashing piece (just above the corrugated apron), and some of the water is diverted horizontally and off the corners of the flashing onto the membrane underneath (see pic 1).
Matters are made worse as the foam gasket that goes along the side has disintergrated in some places and there doesn't seem to be any foam on the sides on the bottom flashing.

So what i'm going to do is make my own modification to the flashing.

I'm going to purchase some replacement foam strips & when the weather is dry, i'm going replace the foam gasket all around and extend the foam strips further down the corrugated apron and add another foam strip barrier that is going to be covered by the tile in the corners (see the the yellow lines in the 2nd pic).

This should hopefully minimise the run off water that's running off on to the membrane!


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Hi there did you get to the bottom of this leak, i have almost the exact problem you have described here


I also have this problem. The foam had disintegrated allowing water (and debris, leaves, twigs etc) to get in under the tiles onto the membrane. I replaced the foam with strips of foam padding that i had, spray glued onto the channel. I'm going to wait for a few weeks to see if it works.
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hi KH904 did the replacement foam work. I spoke to Velux about foam disintegrating on my 7 year old windows and they made no comments like they were aware of it happening. But reading your comments and others who have posted here it seems like a generic issue with the foam. I'm still awaiting a response from Velux
I also have the same problem, was wondering if anybody had any luck with the foam?
I had a builder friend who told me he's had loads on issues with the foam rubber disintegrating. He said the smaller gulley was allowing rain water to flow across it into onto the roof side. The foam in my case had become detached and done little to keep the rain out. So having dealt with this issue on a number of occasions my builder removed the useless bit of foam and cemented inside the second gulley (like you would a verge at the end on a roof). This stopped the rain. I did buy a replacement foam rubber but didn't insert it as I thought it was an inherent flaw with Velux design.
I cut strips of seating foam and spray glued it on and it has worked for the last 2 months, even in some torrential rain and high winds. It has stopped the leaking. I'm going to get the proper stuff (linked by Steve above) and replace it with that.
The problem with a lot of leaking skylights is they were installed by the builder and he didn't bother fitting the BFX collar.

On another note Velux are due to launch a new flashing kit which will go down to 10° so should help eliminate these problems.

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