Strange situation discovered while tracking down damp issue

[WabbitPoo]

I have rain coming down the inside face of the outer skin of my rendered house. I can JUST about see up into the cavity above the window that is in the damp wall, having removed the plaster from the window reveal. With a torch I can see what I think is a horizontal sheet of what looks like slate (its slate-gray, at any rate) sitting across the top of the two concrete lintels. Water has gathered on its underside, which is what I can see with the torch.

Granted, I need to find the source of water ingress, but I was wondering why there would be anything to bridge the cavity like that, given its a rendered property (and has been since it was built in the 50s)

 

[SpecialK]

Possibly to cap the cavity? It could be asbestos...
The water may be finding its way to your roof felt and then down into the cavity? The felt tends to rot and not sit in the gutters anymore.

 

[KenGMac]

WabbitPoo, good evening [again] have not seen you on the board for a while?? -- not stalking but your screen name resonates.

In 50s houses, the window lintels were invariably a so called " boot lintel " where there is a two part lintel, the inner lintel has a projection on its lower side this projection bridges the cavity and touches the outer lintel, the outer lintel is a standard rectangular shape. You may have two rectangular lintels??

There is a DPC that was draped down and over the inner lintel projection thus any cavity water was drained out between the inner [boot] and the outer [rectangular] lintel.

Now?? the DPC was a lead cored bituminous felt which can and does fail over time this allows water in the cavity to get at the inner leaf of brick and hence the dampness. This old lead cored DPC cracks, and becomes very, very brittle, do NOT poke at it !!! as / when removed it acts like a thick egg shell. It matches the colour you describe.

Rain water can be entering above the offending window by cracks and micro cracks in the external render, or as posted by SpecialK above from the roof felt dumping water from the roof / Cavity bridging ?

You may be able to see more if you use a small powerful torch + a small mirror??

As for repair? problematic if my Diatribe above is correct ???

Ken.

 

[WabbitPoo]

thanks for the info. why bridge a cavity? with a brick exterior I get that a cavity tray is used, but rendered? There's nowhere for the water to go (ie no weep holes).

Anyway, having looked at pics of a boot lintel that's not what I have...the outer skin's lintel is a full 12" high (I can't see in to assess the height of the inner one). This just looks like there is a bridge across the top of them both......

Oh, and there is no felt under the slates on any of our roofs....don't know if that's how it was always done here in windy Wales. I suspect water is getting under the very (exposed) edge of the slates that finish at the edge of the roof (this is a gable end).

 

[dontbelieveawordofit]

it’s like asking why bridge a cavity wall with a wall tie?
you said yourself water is running down the inside of the outer leaf.
without the bridge between the two lintels water would settle on top of your window frame and run inside the house.
the bridging material used in your house is an older version of a modern cavity tray. not very good as theyre seldom shaped levelled or angled correctly and water will invariably run of one way or the other instead of out and cause a damp issue one side or the other.

 

[WabbitPoo]

the point is, there is no "out" to run off into as its always been rendered. Admittedly, my focus is on finding the source of the issue. The outer kin also has what appears to be a layer of felt stuck to it (on the inside, of course) as some sort of vertical membrane, though not sure what good it does

 

[^woody^]

Cavities were traditionally closed at the eaves with slate and a fillet or bricks leant back across the cavity.

Water does run down the back of the outer leaf in all cavity walls once saturation is achieved. However you should check the render or the eaves felt for ingress points if you have seen it stream down right from the top of the wall.

 

[dontbelieveawordofit]

the point is, there is no "out" to run off into as its always been rendered. Admittedly, my focus is on finding the source of the issue. The outer kin also has what appears to be a layer of felt stuck to it (on the inside, of course) as some sort of vertical membrane, though not sure what good it does

out as in outwards . is this just a rant against historical building practices in general or do you have an actual question?

 

[WabbitPoo]

Cavities were traditionally closed at the eaves with slate and a fillet or bricks leant back across the cavity.

Water does run down the back of the outer leaf in all cavity walls once saturation is achieved. However you should check the render or the eaves felt for ingress points if you have seen it stream down right from the top of the wall.

Thanks. Its getting access that's the issue - I know its dry within the cavity just above the ceiling (in the loft) so its coming in lower than that. I'll check the mortar fillets that the end slates have been bedded onto along the edge of the gable. Thanks. I was just wondering what a bridge just over the lintels could be doing. Not that it really matters!

 

[KenGMac]

WabbitPoo, good evening, again.

Back in the day [I can remember them, just?] the outer leaf of a cavity wall was "Considered" damp / wet / and at times, saturated, the air gap of the cavity kept this dampness away from the inner leaf, as did / do twisted shanks on wall ties.

The water on the inner face of the outer leaf, would simply keep on running down that face, right down to and below the DPC in the wall where it would dissipate through the brick into the surrounding ground, there being a void [the cavity] between the DPM and ground level. Realistically the total volume of water tracking down Via this scenario is very limited.

As for openings in external walls, windows and doors Etc. the "opening" has to be protected from any potential dampness / water on the inner face of the outer leaf to this end, a DPC is placed between the two lintels, this DPC MUST ! ! shed any water in the cavity OUTWARDS ! ! This is achieved by, in your case the two lintels will be different heights, the inner lintel being higher than the outer to achieve the required outward fall.

As for the material you report being noted down the sides of the window, this will almost certainly be another bit of DPC this vertical strip is there to protect the sides of the window, the top of this bit of DPC is set below the lintel. Bottom line was that you were wrapping the Window / door frame and keeping it away from the [potentially] wet / damp outer leafs inner face.

You mentioned the lack of weep holes, in the case of the lintel DPC any water gathering would shed out if it could not escape above the window, it would pool and eventually be shed sideways to keep on dripping down the internal face of the outer leaf, hence the DPC in the vertical position, but? the lintel DPC would generally be taken about one brick width past the end of the lintel.

Hope this [almost ancient history?] assists?

Ken.

 

[WabbitPoo]

It does, thank you very much. And sorry for the late reply - been busy with looking for the source of water ingress.