Cables run in Cavity Walls

[ExArmy]

You talking about this??

This is just another old wives tale, You could say the same about the metal ties the brickies use or the insulation materials that fills the void. The only time your going to get damp between walls, is when the outer wall (or small area of it) is no longer watertight, eg ...unfilled holes, pointing failure etc!!

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not true, wall ties have little zig zags on them so the water drips off in the middle of the cavity. it is a fact that things bridging the cavity can cause damp problems, i've seen it enough times. even on a new build where the brickies had not cleaned the snots off the ties, damp was coming right through as the outer wall was not rendered yet. and as for cavity wall insulation that fills the cavity, that certainly causes damp problems and theres loads on the internet about it.

 

[Guest55]

banging in a couple of t&e's between 2 walls doesnt even make it into my top 50 bodges and shortcuts.
bridging damp ? get real lol.

 

[ExArmy]

bridging the cavity can cause damp problems. fact. if you disagree your wrong!

 

[Silly Sausage]

not true, wall ties have little zig zags on them so the water drips off in the middle of the cavity. it is a fact that things bridging the cavity can cause damp problems, i've seen it enough times. even on a new build where the brickies had not cleaned the snots off the ties, damp was coming right through as the outer wall was not rendered yet. and as for cavity wall insulation that fills the cavity, that certainly causes damp problems and theres loads on the internet about it.

Agree with the 1st bit.
My house is early 1900s, two brick leafs, mortar filling the tiny gap between them, but the house isn't riddled with damp.
The little building technology I know..., it's more to do with the breathability of the walls and not having running water flowing down the walls.

 

[the oracle]

That may be your opinion, BUT, that is what the current teaching is, and has been, for the last 8 years that I know of. It is laid out in the syllabus for the C & G 2330 course, and will be in the C & G 2365. And, as I said, Building Inspectors will pull electricians up on it, so I think it is wise to discourage it, rather than risk the wrath of an angry Inspector ! Don't you?

 

[thekingiam]

ok time to put my hands up! cavity wall fed from upstairs bedroom under floor boards going down to socket in added conservatory. i rewired this and thought just take cables where they had been before as only about a metre if that down to internal consevatory, am i a bad person?

 

[thekingiam]

oh yeah front room was running in external wall so checked original cable was ok,left in place and connected to new wirring using mf box under upstairs floor boards.ok?

 

[Richard Burns]

Considering what you could have done this, I would say, is not a problem, if you can avoid it then yes do not run cables in the cavity, but also be realistic about installation.
Just don't use it for your assessment!:angel_smile:

 

[richy3333]

NICEIC Snags book (so it must be right )quotes Regs:
522.5.3, 522.8.1, 522.8.4, 522.9.1, 522.10.1 and 523.7

for not doing it. Apparently NHBC requirements, section 8.1 S2 also says it is foreboden apart from with meter tails. Considered bad practice as others have said.

 

[SPARTYKUS]

Yo Richy3333 you iz on fire today!

 

[rich.250]

only thing i'd run in the cavity is tails when doing board changes and there are only 16mm tails.

16 mm tails are more than likely fine in the majority of properties in the uk.
As for cables bridging the cavity causing damp problems ive seen it first hand!! In and older property.
I would Never run a cable in a cavity!!

 

[richy3333]

Yo Richy3333 you iz on fire today!

Glad you can SEE that

 

[Engineer54]

not true, wall ties have little zig zags on them so the water drips off in the middle of the cavity. it is a fact that things bridging the cavity can cause damp problems, i've seen it enough times. even on a new build where the brickies had not cleaned the snots off the ties, damp was coming right through as the outer wall was not rendered yet. and as for cavity wall insulation that fills the cavity, that certainly causes damp problems and theres loads on the internet about it.

They might have now but they didn't before, they used to be solid affairs. So what are you saying that the outer brick skin is going to be sodden with water, ...Not on your Nelly, the only time water is going to enter cavity space above a damp proof membrane is when there is unsealed openings in the outer skin or if the wall needs re-pointing.

All this cables run in cavities causes damp in the house is just absolute rubbish. Not good practice it maybe, but for other good reasons ...not because they cause damp!!

 

[ExArmy]

They might have now but they didn't before, they used to be solid affairs. So what are you saying that the outer brick skin is going to be sodden with water, ...Not on your Nelly, the only time water is going to enter cavity space above a damp proof membrane is when there is unsealed openings in the outer skin or if the wall needs re-pointing.

All this cables run in cavities causes damp in the house is just absolute rubbish. Not good practice it maybe, but for other good reasons ...not because they cause damp!!

condensation forms in the inside of the outer leaf, this will then drip down to the bottom, if there's something bridging the cavity then it will move across to the inner leaf. also driving rain can penetrate small cracks in the render or pointing, which will cause the outer leaf to get wet and again moisture will drip down the inside of the cavity and if it comes across something bridging the cavity then it will move across. now in an ideal world the outer leaf would be completely watertight, but over time problems can develop with guttering, fascias, pointing, flashings, render etc, and in those cases water gets in, now if the cavity is clear then it will just drip down to the bottom where it will do no harm, but if it can get across the cavity then it will and start soaking the inner leaf.
Ive seen things bridging the cavity enough times to know what i'm talking about, no amount of people on a forum telling me it's an old wives tale or to "get real lol" is going to change my mind. if you think you can just do anything you like to a cavity and then if you end up with damp problems then it'll be down to the outer leaf letting water in and in no way related to whatever there is now bridging the cavity( be it insulation, cables, pipes etc) then you need to ask yourself why cavity walls were invented in the first place, and had the "thing" bridging the cavity been there then would damp be able to get accross?
im not saying anything crossing a cavity will cause damp, if i have to drill through a cavity then I drill from the outside at an upwards angle (about 30 degrees) that way if any moisture were to get on the cable then it would just drip off as it can't travel uphill.

 

[Rockingit]

The only thing that I can add to this debate is that back in all the storms we had a few months ago, I had an RCD trip out in my own house.... what was happening is that a 10mm shower cable fed via the cavity (before my time) was acting as a very nice runway for water getting in somewhere (hopefully now sealed up!), and that water was travelling straight into the DB.

But, I got into a bit of a scrap with an elecsa assessor a few years ago when he demanded that a short (<1m) length of tails that I had buried in the wall from old position to new get redone to a proveable >50mm depth (had installed them at about 30mm and put some steel plate in front). I pointed out that there wouldn't be an awful lot of wall left given the dia of the tails and he said just to run them in the cavity instead. I disagreed due to insulation and we ended up compromising by me using a thicker plate in front.