Running Cables in a Cavity

[LED Lighting]

Is it allowed under BS7671 to run cables into a cavity, if it is allowed is there any thing you need to be aware of? or do?

 

[uksparks]

Yes you can run cables in cavities so long as its in a proper containment and supported throughout its length. Although not the best thing to do, sometimes it is the only option.

I have run cables in cavities, firstly I put a 50mm pipe, well five of them actually up from the garage to the first floor (about 3 ft) then cemented them into the wall neatly to mount the board on top.

You should not just run / drop cables into cavities as you do not know what is going to come into contact with it, for example falling brick debris, blown poly insulation which will react with the PVC on the cable. So basically just make sure its in some form of ducting on its own away from damage.

Don't forget grouping factors though if you are bunching a load of cables together, but then again it depends how long a distance it is.

 

[telectrix]

even in pipe though, cables are not properly supported.

 

[Risteard]

Never mind whether it is permitted by BS 7671. The Building Regulations might be more relevant.

Aside from causing mechanical damage to the cable there is the danger of bridging the cavity.

 

[telectrix]

cavity is already bridged by wall ties and whatever crap the builder has chucked in.

 

[uksparks]

See the pics below to see what I did, like I say, that's 50mm pipe, it was a pig and a half getting it in the cavity though. Oh i got the pipe from the garden center. The holes in the joists were already there by the way, i didn't drill them like that!

 

[uksparks]

even in pipe though, cables are not properly supported.

I agree, I would only do it if it was a couple of feet like in my photos, anything more and its not supported particularly well.

 

[uksparks]

cavity is already bridged by wall ties and whatever crap the builder has chucked in.

Yes indeed, personally I wouldn't worry too much about bridging the cavity as like you say there's all the other crap and insulation in there anyway. You have to do whats best for the job, if its the only way that's practical, then you do it.

 

[Pete999]

Used to run cables in the cavity on all new builds to get away from chasing in, back in the good old days late 60s early 70s, but I'm reminiscing now you will have to forgive an old man harping back to the days when men were men and there wasn't any 5wws :nopity::joker:

 

[7029 dave]

Used to run cables in the cavity on all new builds to get away from chasing in, back in the good old days late 60s early 70s, but I'm reminiscing now you will have to forgive an old man harping back to the days when men were men and there wasn't any 5wws :nopity::joker:

Yes Pete, pulled a lot out and made on with new t&e cable on a lot of rewires, and I would still!!, sorry madam got to tear your house part because regs wont allow it, nonsense. Sometimes you have to bow with the breeze . lol

 

[Pete999]

Yes Pete, pulled a lot out and made on with new t&e cable on a lot of rewires, and I would still!!, sorry madam got to tear your house part because regs wont allow it, nonsense. Sometimes you have to bow with the breeze . lol

"those were the days" Mary Hopkin

 

[7029 dave]

Those were the days my friend, la la laa la.

 

[telectrix]

aye. £20/week was a good wage. petrol 5 bob a gallon ( yes, gallon, not silly french litre ), them's deffo were the days.

 

[Pete999]

Id wished they'd never ended really

 

[DPG]

cavity is already bridged by wall ties and whatever crap the builder has chucked in.

Cavity ties have a drip loop meaning any moisture wicked in from the outer skin is dripped down and not carried through to the inside. Unsupported cables can bridge the inner and outer and transfer water between the skins.
And there shouldn't be any crap in the cavity, but obviously we don't live in an ideal world with caring builders! Daz

 

[uksparks]

I was wondering why they had that twist in the middle.

 

[Octopus]

So what happens when the green brigade fill up the cavity with insulation - that bridges the gap!

 

[Engineer54]

So what happens when the green brigade fill up the cavity with insulation - that bridges the gap!

Shush now, that don't count!! Nore does the sloped mortar, that lands on those cavity ties that either bridges the gap, or nullifies any drip effect of the tie.... lol!!

 

[davesparks]

Blown insulation bridges the gap!

However the insulation in newly built cavity walls is supposed to be fixed against the external skin to prevent it from bridging the gap.

 

[Engineer54]

Blown insulation bridges the gap!

However the insulation in newly built cavity walls is supposed to be fixed against the external skin to prevent it from bridging the gap.

To be honest it doesn't matter if the two walls are bridged. It's only becomes a problem damp wise, when the outer external walls are in a bad condition, with open penetrations, cracks and in serious need of repair and/or pointing...

 

[davesparks]

there is of course the condensation problem that turns up everywhere now that rooms have to be insulated to hell and back and be airtight etc.

I just don't understand why we have to test new houses to ensure they are airtight and then add trickle vents to every window, masses of mechanical ventilation, open air vents for fireplaces and gas fires to make up for the fact they are now airtight and can't breathe.