Victorian Terrace Persistent Minor Roof Leak

We’ve been having slight but ongoing issues with what we think is a leaking roof in our Victorian terrace. The layout is a typical Victorian terrace, and the room with the issue is the rear room on the first floor. We are end of terrace so the side wall is exposed, which may be an additional factor. Brown staining is coming through the paintwork on the long wall that sits below the capstones, and reappears even after repainting (as per photo 1)

The stains are not especially localised to a particular patch of the wall - there must be good 6-12 affected areas spread along a circa 3m run of wall (some are tiny, being less than a 5p coin). Most stains are near the top of the wall, but some are a good 50-75cm down without any damage to the wall above. Even though the damage is not dramatic, the fact that the stains are spread over such an area makes me think the water ingress issue is not necessarily limited to a single point on the roof.

About 12 months ago we had some repair work carried out - the capstones at the far end of the roof were lifted and re-mortared, a few damaged bricks were replaced, and general repointing was undertaken. This seems to have improved the situation, but has clearly not solved it.

There are no stains elsewhere in the room including the sloping ceiling, so we are assuming the leak is limited to the side wall\capstone\flashing area rather than the general wider roof and tiles.

I’ve attached a few other photos of the roof, attempting to show the general condition. Some of the mortar immediately under the capstones seems to come loose occasionally, so that may be related.

If anyone has experience of similar issues or related advice that would be appreciated. We don’t want to go unnecessarily overboard, but, having been through minor repairs once, we want to be sure that the next attempt is successful.

Looks like a new roof?

The capstones should not be coming loose, does the lead run right over the wall or is it let in either side?
If the stones are sitting on lead, they will perpetually come loose..... not that the lead should allow water in anyway, assuming it is adequately lapped.

I'd have said the wall should be 2-3 courses above where the lead is let in, and then the capstones sitting on that. The wall looks too low, as if the top of the wall needed rebuilding and someone decided it would be easier just to remove it....
A look at other houses along the terrace might give you a clue... perhaps I'm offbeam.

Leaving that aside, I wonder if the wall was wetted before the roof was redone and has still not quite dried out?
Can you get into the attic, or does the ceiling underly the roof?

You might buy a moisture meter ... eBay... and stick it into the wall, see if it tells you anything. Someone with more knowledge of which meter will hopefully come along soon.

Ivor

What is the pitch of the roof? And what are the recommended maximum angle and the headlap for the tiles? I guess these are some man-made tile, not slate?

Is the vertical end wall on the other side of the capstones? If so, what does the overhang of the capstones look like - does it have a decent drip edge?

Sorry for all the questions, but I must confess that I am slightly puzzled by what appears to be an attachment hole at the bottom of each slate. If it is, how does it not let in a little bit of water? Perhaps it's some clever modern attachment that I've not come across. I've only done welsh slate roofing, and took great care that the headlap was properly covering all the nails by a good distance.

MatthewC said:

Sorry for all the questions, but I must confess that I am slightly puzzled by what appears to be an attachment hole at the bottom of each slate.

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Often “man made” slates have the hole at the bottom, usually a copper rivet is used in that hole to hold the leading edge down.

EDIT: even managed to find a reference - look at me

http://www.roofconsult.co.uk/articles/tiling/tips20.htm

Thanks for the responses. Here’s a bit of extra detail based on the questions:

88v8 said:

Looks like a new roof?

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Yes, the roof is definitely not original, but it’s certainly not ‘new’ either. It predates our time at the property, and I would guess that it is circa 20+ years old.

88v8 said:

The capstones should not be coming loose, does the lead run right over the wall or is it let in either side?

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I don’t have the necessary ladders to reach to that height, plus I need to access my neighbour’s property every time access to the side wall is required, so visibility on the other side is limited. I believe the lead does not run all the way under the capstones and through to the other side (i.e. it terminates some way under the capstones.)

I have attached another photo giving some further view of what is happening on the other side.

88v8 said:

I'd have said the wall should be 2-3 courses above where the lead is let in, and then the capstones sitting on that. The wall looks too low, as if the top of the wall needed rebuilding and someone decided it would be easier just to remove it....

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I can’t be certain, but I think no modifications have been done to the roof line/height of the capstones. The capstones sit at an equivalent point on neighbouring houses, so it doesn’t look like they’ve been lowered on our roof.

88v8 said:

I wonder if the wall was wetted before the roof was redone and has still not quite dried out?

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Given that the roof must be well over a decade old at minimum, I’m hoping (assuming?) this is not the case.

88v8 said:

You might buy a moisture meter ... eBay... and stick it into the wall, see if it tells you anything. Someone with more knowledge of which meter will hopefully come along soon.

Click to expand...

I’ve played around with a cheap moisture meter (albeit its primary purpose is for wood), and not found anything of note. There’s no obvious smell of damp either. The plaster on the inside wall is blown in places though, so clearly something has happened at some point. I believe there may have once been ivy growing up that side of the house, so perhaps it’s a residual issue from that?

MatthewC said:

What is the pitch of the roof? And what are the recommended maximum angle and the headlap for the tiles? I guess these are some man-made tile, not slate?

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I’m not certain of the roof pitch, but on the shallow side. I’ll have to estimate. It’s certainly equivalent to neighbouring properties though. This roof was done before our ownership, so I’m unaware of the recommended installations specs for the tiles. But, yes, they are definitely man-made (unfortunately).

MatthewC said:

Is the vertical end wall on the other side of the capstones? If so, what does the overhang of the capstones look like - does it have a decent drip edge?

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Access is tricky (insufficient ladders etc), but I’ve attached a photo that provides a glimpse of what is going on with the vertical side wall. Note, this picture was taken before the previous repair work, so the visibly deteriorating brickwork and pointing was tidied up last time. Other than that is is largely unchanged though.

The overhang of the capstone is very minimal, and it looks like its brick all the way up to the capstone without any coverage/flashing etc. I’m not 100% what a drip edge is, but if it’s what I think it is then we don’t have one.

I’m guessing that from all the points raised so far, the issue is potentially related to this.

MatthewC said:

Sorry for all the questions, but I must confess that I am slightly puzzled by what appears to be an attachment hole at the bottom of each slate. If it is, how does it not let in a little bit of water? Perhaps it's some clever modern attachment that I've not come across. I've only done welsh slate roofing, and took great care that the headlap was properly covering all the nails by a good distance.

Click to expand...

Although having undertaken many aspects of property renovation ourselves, owing to the height, roofing is one of things we’ve not got involved with. Consequently, my knowledge is limited, and so I can’t really advise how the tiles are fixed. From researching online I read of similar installations where it is suggested that the tiles are not upside down, but those holes are for the copper rivets to secure the bottom edge. Additionally, our original surveyors report suggested they are "compound slates and fitted top and bottom with tingle pins". I'm assuming they are therefore meant to be like that. Also, these tiles adorn both our rear and front roofs, so if there was a major problem owing to the attachment hole I assume we’d have had major issues by now!

a twig said:

MatthewC said:

Sorry for all the questions, but I must confess that I am slightly puzzled by what appears to be an attachment hole at the bottom of each slate.

Click to expand...

Often “man made” slates have the hole at the bottom, usually a copper rivet is used in that hole to hold the leading edge down.

EDIT: even managed to find a reference - look at me

http://www.roofconsult.co.uk/articles/tiling/tips20.htm

Click to expand...

It looks like I was beaten to it regarding the explanation for the lower hole.

It's misleading to say the hole and copper rivit are to hold the slate "down".
It's to hold the slate to the slates underneath, not nailed down onto the batten.

CliffordPope said:

It's misleading to say the hole and copper rivit are to hold the slate "down".
It's to hold the slate to the slates underneath, not nailed down onto the batten.

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If you say so I would suggest that anyone who was misled would quickly realise their misunderstanding when trying to hammer a copper rivet into a batten :lol:

Two observations -
Are we sure that the wall is 9" brickwork? The parapet under the capstones seems to be single brick.
The staining looks very dark in colour. Could it be rust from a nail under the plaster?
CB

charlieboy said:

Are we sure that the wall is 9" brickwork? The parapet under the capstones seems to be single brick.

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The end wall in the room (perpendicular to the line of capstones and wall with staining) has a window. External measurements from the edge of the vertical side wall to the window give 90cm, and the equivalent inside measurement in circa 65cm. This suggests about 25cm is consumed by brickwork and plaster, which seems about right for 9" brickwork. Also, I'm not sure exactly what bonding the brickwork is, but it does seem to have headers as well as stretchers.

However, you are correct that the parapet is single brick.

charlieboy said:

The staining looks very dark in colour. Could it be rust from a nail under the plaster?
CB

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Seems unlikely. We have several of these dotted about the wall (the photographed one is probably the most intense). I cut out a small patch of plaster on one stain to check the brickwork behind. Admittedly its only a small area but I found nothing obvious.

a twig said:

If you say so I would suggest that anyone who was misled would quickly realise their misunderstanding when trying to hammer a copper rivet into a batten :lol:

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It's readers who know nothing about the system but might imagine that the holes could be a possible source of water leak?

Years ago the old asbestos slates didn't have the tail rivets, until the ends started to curl up.

At present, my thinking is to have the capstones removed and re-mortared, but, at the same time, have flashing lipped under that then protects the vertical side wall (probably covering the first couple of courses of brickwork).

This essentially assumes that the pitched side of the roof is fine, and that the issue is with the capstones and vertical side of the wall.

Does this sound a reasonable plan of action?

Yes and no.

Unless the bricks are porous one wonder why it should be necessary.
And given that it's only single brick, with lead under the capstones there will be less cement bond to hold them in place.

I would renew the bricks. Use engineering bricks, no additional lead.
Engineering bricks are not absorbent.

If the wall is the source of the problem, that should put an end to it.

Ivor

88v8 said:

And given that it's only single brick, with lead under the capstones there will be less cement bond to hold them in place.

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This is a good point - it could exacerbate what is potentially already the cause of the issue.

88v8 said:

I would renew the bricks. Use engineering bricks, no additional lead.
Engineering bricks are not absorbent.

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I assume we're only talking of replacing the parapet bricks (i.e. the top course only) with engineering bricks, and not any lower?

J_Ashley said:

88v8 said:

And given that it's only single brick, with lead under the capstones there will be less cement bond to hold them in place.

Click to expand...

This is a good point - it could exacerbate what is potentially already the cause of the issue.

88v8 said:

I would renew the bricks. Use engineering bricks, no additional lead.
Engineering bricks are not absorbent.

Click to expand...

I assume we're only talking of replacing the parapet bricks (i.e. the top course only) with engineering bricks, and not any lower?

Click to expand...

Yes.
Just the top courses that are exposed to the weather.

Ivor