Cables in cavities

[NIZMO]

Hy ,
I know its probably been asked but ive done a search and couldent find it , is it considerd bad practice or against regs to run or drop cables down/in wall cavities . I had a feeling you were not allowed two although i cant think why as it would appear to be safer as it would be hard to drill or nail into the cable .
Thanks

 

[comms]

Nothing in the regs unless you go down the route of cable support / damage by items in the cavity such as wall ties.
But I belive building control get a snot on sometimes & quote building regulation C (think thats what it is) something to do with transfer of moisture from external wall to internal wall.
Something else to consider is cavity insulation, if it's there you'll have to rate cable accordingly. But in the real world yes you will find cables run in the cavity at some point but it is considered a bad practice.

 

[ban-all-sheds]

There are two issues:

1) You won't be able to support the cable - 2.5mm² T/E for example should be clipped every 40cm on vertical runs.

2) Someone might later put cavity insulation in which could damage the cable sheath or reduce its capacity.

 

[Qedelec]

Bit far fetched I know, but there was a case of cavity insulation (foam), being added which caused a damp patch on the inner wall. The cause was a builders lunch pack on a tie, causing a void in the insulation and allowing damp to traverse to the inside. It is possible cables could cause the same problem.
So if in doubt, leave it out.

 

[NIZMO]

Thanks people , i appreciate your responce . Id rather know whats the right n wrong way to do things ,
Thanx

 

[s999]

Are you allowed to run satellite cable down the cavity?

Surely theres no harm in this...... is there???

Most satellite installers drill a hole through both walls and pass the satellite cable through.

So the satellite cable is pretty much in the cavity in most households anyway... (only a bit though).

I thought I'd draw a picture too.

 

[viewer]

Extra point to consider. I've seen quite a few rodent nests (and associated damage) in cavities. They love chewing cables.
V

 

[s999]

I'm pretty sure there aren't any rodents in my cavity..... (I hope).

Like I said my satellite cable passes through my cavity anyway because of the hole that the satellite man drilled through both walls.

I'm really thinking about running the satellite cable down the cavity......

 

[Steve]

Like I said my satellite cable passes through my cavity anyway because of the hole that the satellite man drilled through both walls.

Okay, now look around your house and see how many other cables run THROUGH the cavity!

Mains electric intake
Aerial
Phone
CATV
Outside lights
Alarm
lectric to shed

I could go on, but the point is, how else did you think they get into your house? Its not exactly professional looking to drill a hole through the corner of a window frame, for example. Most respectable tradesmen will drill through the bricks.

Running cables DOWN or ALONG the cavity, though, is not good. issues already raised such as rodents or insects are a problem that you may not know about. Damp, and cavity wall insulation, will have a bad effect on the cable, and someone could add the CWI in future, without knowing about the cable you have run. With ELV applications such as phone or alarm cables, this is not usually a problem, and wont cause a fire, but running mains cables in insulation or damp conditions may cause them to build up heat or degrade and possibly melt or break down and cause a fire.

 

[Adam_151]

I'm pretty sure there aren't any rodents in my cavity..... (I hope).

Glad to hear it, wouldn't like the thought of a fellow forum poster being a complete weirdo...

 

[viewer]

Glad you've nothing in your cavity
Here's a true story. Some time ago I worked for a local council. At the time the police were building a multistorey block. A local resident came in to the council offices and complained that the building was spoiling his television picture. We sent him away (the transmitter was the other direction). Through the next few months the building went up and every week the poor man came in to complain that his TV picture was getting worse. He got steadily more upset and more aggressive. At last the building was finished and on the day of the topping out ceremony he charged into the council offices swearing and shouting. His picture had now gone completely. To pacify him, we went to look. Sure enough just snow on his screen. The neighbours was OK. Examination showed that the cable from aerial went into the cavity, down to DPC and up to the lounge. The varmints had chewed completely through the cable (they'd got in through a broken drain). Just luck that the steady demolition of the co-axial coincided with the building project. He didn't believe us of course. One day I'll write my memoirs, but I doubt decent people would believe those either.
Have fun.

 

[sandwell]

I have got cables in the cavity. Installed by a qualified electrical contractor. It was the easiest and the obvious way to do the job. But I now have the problem that foam insulation cannot be installed. Not too bothered about it though, I doubt if it would make the house any warmer, or reduce the fuel bills.

 

[TeesdaleSpark]

It's bad practice because you are breaching the cavity as well as adverse effects of insulation on the cables. Also how do you draw the cables in without damiging them. I'm doing inspections for a local authority and if I find cables in the cavity the house will be rewired.

NICEIC TECHNICAL MANUAL
NHBC Requirements
It is noteworthy that the National House-Building Council states, in Section 8.1 - S2 of NHBC Standards, that no cables other than electricity meter tails are to be located in the cavity of an external wall. Where meter tails do have to pass through the cavity, however, this does not preclude the requirements of BS 7671 referred to in this topic having to be met.


APPROVED DOCUMENT C
Cavity external walls
5.12 Any external cavity wall will meet the
requirement if the outer leaf is separated from
the inner leaf by a drained air space, or in any
other way which will prevent precipitation from
being carried to the inner leaf.
Technical solution
5.13 The construction of a cavity external wall
could include:
a) outer leaf masonry (bricks, blocks, stone
or manufactured stone); and
b) cavity at least 50mm wide. The cavity is
to be bridged only by wall ties, cavity trays
provided to prevent moisture being carried to
the inner leaf (see paragraph 5.15 for cavity
insulation), and cavity barriers, firestops and
cavity closures, where appropriate; and
c) inner leaf masonry or frame with lining.

 

[ban-all-sheds]

APPROVED DOCUMENT C
Cavity external walls

The cavity is
to be bridged only by wall ties, cavity trays
provided to prevent moisture being carried to
the inner leaf (see paragraph 5.15 for cavity
insulation), and cavity barriers, firestops and
cavity closures, where appropriate;

So how do you get TV aerial etc cables through? Phone cables? Cables for external lights? Cables for doorbell pushes? Cables for alarm sounders? Cables for supplies to outbuildings? Water pipes for external taps? Pipes and cables for air-conditioning units?

 

[Pensdown]

I'm doing inspections for a local authority and if I find cables in the cavity the house will be rewired

That a complete waste of public money. No wonder rates are so high