Rain leak at gable end roof to wall joint

[Me!]

For all the years we’ve lived in this house we have had a problem with rain leaking in at one gable end of the roof. I have fixed various problems with it, and reduced the leakage a lot, but there is one problem that I don’t know how to fix.
When wind driven rain hits the gable from the angle of this photo, it seems to get pushed through the join between the red arrows and into the hollow timber framed wall. Then, particularly at the purlins it drips and runs down inside the hollow wall until it gets to the blue line. At the blue line, below this point the wall has been rebuilt (in Victorian times I would guess) with solid 9” brickwork and so it can’t drip any further and runs out into the bedroom around the window by the purple line. To be clear, this only happens perhaps once or twice a year, but when it does it is not just a few drips, and we can get a pint or so collected on the bedroom window board.
The soffit boards, are in good condition and last summer I repaired the edge of the render that adjoins them to make the joint a good fit, and repainted the gable wall and soffits, bargeboards purlin ends, caps etc. What I have not done is resorted to squirting any kind of mastic, silicon or expanding foam in there as I don’t believe they would stay stuck for long when exposed to the natural movement of the join. But maybe I'm wrong and that is what I should be doing.
To add to this, my neighbour has a new-build (1990’s) oak framed house, with a gable end facing the same direction, and his also leaks!
So, my question is please, how is this joint supposed to be made to repel driving rain?
Many thanks.



PS. The roof is pantiles, sorry about the snow covering them in the only photo I have handy.

 

[Feltwell]

Although it’s difficult to see much in that picture, if you didn’t want to try to seal that joint then the other option is some kind of angled profile that is fixed and sealed to the bottom of the roof only - so it’s free to move against the wall - but any rain that hits it then drips down from its lower edge, below the joint, and harmlessly down the render.

You could have an L shaped profile machined up in timber and then paint it in to match. Rather than a plain L I’d be tempted to have a slightly fancier profile.

So long as it comes down a reasonable distance beneath the joint and it’s close to the wall that should make it much harder for wind blown rain to get up there.

 

[Me!]

I understand what you are saying, and that would work for water being driven sideways on the underside of the soffit, but I think it is water being driven sideways across the gable end wall that is getting in. All the bargeboards are well below the soffits and with well formed drip rails along their bottom edge, and the purlin ends have drip rails cut into them as well.
The roof pitch is steep, it is 35 degrees to the vertical, still with the original timber structure which was presumably thatched originally but now pantiled. But the gable end wall is not quite vertical, it leans at about 10 to 15 degrees back towards the building and to compensate for this the roof overhang at the ridge is more than at the eaves. However this lean does mean that as a wall it catches more than its fair share of rain, which obviously doesn't help.
What I still don't understand though is even on a brand new build, how is a leak at this join avoided? Or is it? I notice that many catnic type lintels have a sloping top to push any water in a cavity wall towards the outer skin. Is this because water does run down the inside of modern cavity walls?

 

[Feltwell]

I see what you mean.

Usually on a brick gable end, at least on the houses I've owned, the brickwork extends upwards beyond the visible boundary between the soffit and brick - and the soffit is fixed to to the bottom of the purlins, so unlike in your case their ends are hidden - so typically the brickwork is built up and around the purlins, which protrude through the gable end and have the fascia boards fixed to them as you have. The brickwork goes pretty much to the top edge of the rafters - so any water blown up there will presumably just run back down again once it's out of the wind in that sheltered area.

If it's a modern truss construction, they fix a ladder like frame to the end truss, which sticks out through the brickwork in a similar way to the purlin ends. It's not that strong though to support the fascia board and final bit of roof, certainly nowhere near as strong as a traditional roof with purlins.

Modern cavities, my understanding is measures like the slope on a catnic lintel are there to deal with any water that does get in, but none should. A bit like why brick ties have the twisted joint facing down - so any water going onto them drips down and away from the inner skin of blockwork - but ideally you don't want any in there to begin with.

As for your situation - tricky. Usually any sealing situation involving movement and leadwork is the way to go, but I don't see how it would work in your case.

If you can live with the visual change (are you listed?) then I'd be thinking of fixing a new soffit to the bottom of your exposed purlin ends, behind your fascia boards - that will give you that sheltered area above it that I describe above - especially if you seal the join with the render (but definitely put ventilation elsewhere - on the other edge behind the fascia boards perhaps) - and ensure that any water that does get in can run down the top of your new soffit, not be trapped anywhere and can drip away harmlessly at the bottom.

Or, you could try the angled profile idea, but don't fix it rigidly in place - use a building adhesive to seal it to both the wall and the existing soffit, to give it maximum potential to move. I'm no expert on modern adhesives, but this stuff gets used on external body joints in caravans and motorhomes, which flex a lot as the body twists, on motorhomes especially. I've used it and it's tenacious stuff.

https://www.toolstation.com/shop/p85566

 

[Me!]

That makes a lot of sense, and yes, an extra soffit could well be the answer. Not on the bottom of the purlins as they are lower than the bottom edge of the bargeboards -


But, that last rafter in the photo that is attached to the bargeboard is 4" deep, so I could easily batten along the inside of that rafter and the outside of the top of the wall at 2" or 3" below the current soffit and add another second soffit at that lower level to create a dead-zone from the wind.

That is a very good idea, many thanks for your help.

 

[MikeG]

A low modulus sealant would work, and I would certainly try this quick, simple and cheap cure first before moving on to more complex and expensive alternatives. If our ancestors had had access to the stuff, they'd have used it.

 

[88v8]

As Mike says, low modulus. Very flexible.
That stuff Feltwell linked, is high modulus. Very grippy on cars, where it's used as a seam sealer, but as flexibility goes it's not very flexible.

The other problem with sealants is priming the surface. Oft neglected, but without the primer, many sealants will soon fail. When sealing cracks, one cannot get the primer into the crack, so this is a problem.
This silicone sealant - Dow Corning C60 - allegedly will manage with no primer. I'd give it a try. Not overpaintable, of course.
https://www.sealantsonline.co.uk/ProductGrp/Dowsil-c60-premium-lm-building-silicone-sealant.
(A good source of sealants, that site).
Alternatively any good quality frame sealant, if a paintable option is wished.

The leak is not just happening a couple of times a year. It may only manifest internally a couple of times a year, but you can bet it's happening more often, the water getting in to a lesser extent and being absorbed by the structure before it reaches the interior.
Damage ensues, unseen.
Water is a patient destroyer, it has all the time in the world.
It brings its friends, Mr Rot, and Mr Worm.

Ivor

 

[Feltwell]

As Mike says, low modulus. Very flexible.
That stuff Feltwell linked, is high modulus. Very grippy on cars, where it's used as a seam sealer, but as flexibility goes it's not very flexible.

Yes, I agree, my mistake. The stuff I linked to is labelled as high modulus but actually seems pretty flexible to me - I've used quite a bit of it on a motorhome - but what they sell as low modulus should be even more so.

This one comes in brown and claims to stick to what you have there:-

https://www.toolstation.com/shop/p97204

Or this is the low modulus equivalent to the one I first posted, and comes in a dark grey option:-

https://www.toolstation.com/shop/p85598

 

[Me!]

Well, it sounds like a low modulus silicon is worth a try, so I'll give it a go.
I can borrow a scaffold tower tomorrow, so that means I need to get the silicon this afternoon, and that means I can only realistically get it from Screwfix. Unfortunately they don't stock any of the ones that have been recommended, however they do have this one which claims "Low modulus silicone that gives excellent, unprimed adhesion to both porous and non-porous substrates. Suitable for weather sealing and expansion joints."
https://www.screwfix.com/p/dow-791-weatherproofing-silicone-sealant-brown-310ml/76697

If anyone thinks that is the wrong stuff to use, then please shout in the next couple of hours before I buy it!

 

[Feltwell]

Looks fine to me.

Or buy the Toolstation stuff and get it delivered in the morning, their cut-off is quite late (8pm I think). It's 6 and 2 x 3's!

 

[Me!]

Well, I put the silicon in the joint and it certainly seemed to stick well to both surfaces. Now it's just wait and see, but the trouble is knowing how long I will need to wait!

The leak is not just happening a couple of times a year. It may only manifest internally a couple of times a year, but you can bet it's happening more often, the water getting in to a lesser extent and being absorbed by the structure before it reaches the interior.

Because I totally agree with Ivor, I have previously taken some fairly extreme measures to stop these leaks. The inside of this wall is just modern plasterboard, so about 7 or 8 years ago I removed several large sections of it and we have lived with big holes in the internal face of the wall since then so that I could see exactly where each leak actually came through the external wall and then fix it. After many years and many rain storms blowing from different directions we got to a point where nothing leaked in for two consecutive winters and I finally repaired the internal walls and decorated the rooms. Then, the following winter there was a slight trace water staining around the window but only very slight and I thought it may have come through some bad joints in the lead of the window pane. But a couple of weekends ago we had heavy driving rain again and this time it came pouring through the wall.
Extremely annoying!

 

[Feltwell]

Fingers crossed for you!

It's a bit like any job to treat damp I suppose. I've got to hire scaffolding in during next spring to do repairs to a chimney breast, but in reality I won't know if it's been a success until at least a couple of years later - when the chimney breast and ceiling inside (that are currently water stained) have dried out, been decorated, and left for a few months. Patience is not my thing, I want to know straight away if my fix has worked or not! :evil: :lol: