Good Old Delroy, he gets all the best Jobs :)

[Dustydazzler]

 

[Dave OCD]

Nothing in the regs to say you can't but lots of reasons why you shouldn't especially if there is insulation.
niceic say that if you must, then mineral cable would be acceptable.

The usual high quality advice - the most inflexible and difficult cable to try and fish through a cavity that I can think of.

 

[goasis]

The usual high quality advice - the most inflexible and difficult cable to try and fish through a cavity that I can think of.

Whats their reasoning PVC?PVC isnt suitable?

 

[mainline]

Whats their reasoning PVC?PVC isnt suitable?

Pvc reacts with for example polystyrene

 

[goasis]

Pvc reacts with for example polystyrene

ah, those beads that get pumped into cavities sometimes, fair enough.

I only asked because in the video the room has a short wall all the way round, presumably the cavity is open at the top, and i guess with rockwool or celotex in the cavity, so running cables through it would seem a reasonable way to do it in this instance, same as you see in alot of conservatories. Delroy was 'teaching' the new lad and said you weren't allowed to do that but he didn't know why......

 

[Dave OCD]

And there's the risk of unseen damage from any rough or sharp bits of block or cement within the cavity.

 

[Mike Johnson]

The cavity is there to provide a gap and prevent damp from penetrating to the inside skin of the building, wall/brick ties have drips on them to allow the water condensate to reach the cavity tray at the bottom of the wall and drain through the open perps to the outside, its not there for any electricians to run cables in and compromise the drips on the ties.

Do a google search and you will find that cavity's are no longer filled with insulation, it was always a bad idea and many house's have been ruined by the practice.

 

[goasis]

The cavity is there to provide a gap and prevent damp from penetrating to the inside skin of the building, wall/brick ties have drips on them to allow the water condensate to reach the cavity tray at the bottom of the wall and drain through the open perps to the outside, its not there for any electricians to run cables in and compromise the drips on the ties.

Do a google search and you will find that cavity's are no longer filled with insulation, it was always a bad idea and many house's have been ruined by the practice.

Cavity's definitely are still filled with insulation! Regardless of what google may say!!

 

[Pretty Mouth]

The cavity is there to provide a gap and prevent damp from penetrating to the inside skin of the building, wall/brick ties have drips on them to allow the water condensate to reach the cavity tray at the bottom of the wall and drain through the open perps to the outside, its not there for any electricians to run cables in and compromise the drips on the ties.

Do a google search and you will find that cavity's are no longer filled with insulation, it was always a bad idea and many house's have been ruined by the practice.

That's the theory. Real world, even a 9" solid wall doesn't allow significant damp to pass through to the inside, unless it's very exposed to the prevailing wind, or the rainwater goods have failed and are pouring water all down the wall. The odds of significant moisture making its way to the inner leaf of a cavity wall via cables run in the cavity are very low indeed.

I have never heard of cavity trays and weep holes being installed at the base of cavity walls, or of any houses being damaged by cavity insulation. What are your sources for this? Genuinely interested to hear more about this.

 

[pirate]

I think it's fair to say that there is a fairly strong view that cavity wall insulation is not the blessing it was thought to be at first. In particular, poorly installed insulation can have a detrimental effect on some structures, notably timber-frame building, especially if the method used is to pump polystyrene at pressure without proper supervision. I have personally witnessed damage to a few houses caused by such a method.
The polystyrene balls, being preformed and thus not "foaming" into the cavity, do not seem to cause such problems.
However, a cavity wall is there for a purpose, as Mike Johnson says above, with ties to carry moisture away from the inner leaf (as well as tying the 2 leaves together).
It may be rare for water to penetrate from the outer wall to the inner, but I have personal experience of this. Failure of the external pointing and mastic led to penetration of exactly this type in my building which has polystyrene balls installed. The result was considerable moisture affecting the internal plasterwork in some of the flats, black mould and flaking plaster, and the clean-up measures after rectification of the cause were considerable and expensive.
The surveyor appointed to oversee the remedial work was quite clear that the damage would have been far less had the cavity been left clear of insulation, as the insulation allowed the water to track across the cavity, and held it in.

 

[Mike Johnson]

I have never heard of cavity trays and weep holes being installed at the base of cavity walls, or of any houses being damaged by cavity insulation. What are your sources for this? Genuinely interested to hear more about this.

Cavity trays and weep holes are the standard method of draining a cavity, and damage to houses by full fill cavity insulation has been well publicised by the RICS and the Institute of Civil Engineering, you will note below the insulation is only part fill any penetration of this by cables will cause a thermal bridge.

 

[mainline]

That's the theory. Real world, even a 9" solid wall doesn't allow significant damp to pass through to the inside, unless it's very exposed to the prevailing wind, or the rainwater goods have failed and are pouring water all down the wall. The odds of significant moisture making its way to the inner leaf of a cavity wall via cables run in the cavity are very low indeed.

I have never heard of cavity trays and weep holes being installed at the base of cavity walls, or of any houses being damaged by cavity insulation. What are your sources for this? Genuinely interested to hear more about this.

I do a lot of work on barn type conversions with no cavity at all, lots of those walls are around 3ft thick some are coated with a tar like stuff because of water ingression.

 

[Pretty Mouth]

Cavity trays and weep holes are the standard method of draining a cavity, and damage to houses by full fill cavity insulation has been well publicised by the RICS and the Institute of Civil Engineering, you will note below the insulation is only part fill any penetration of this by cables will cause a thermal bridge.

View attachment 96424

Mike this diagram is for radon protection rather than damp, see here: Radon Protection in Above-Ground Environments - https://www.safeguardeurope.com/applications/radon-above-ground

 

[Mike Johnson]

The purpose of the diagram was to show the cavity tray which someone said they had never seen, this is all standard building works you guys need to get out more.

 

[7029 dave]

During my apprentice years we done loads of council houses using the wall cavity as a wire way as more often than not it was quicker and cleaner than chasing (we didn't have twin disc wall chasers back then)

We did to, but they were all fully occupied rewires the council tenants were still living in them back in the good old days, so you had to keep disruption and mess to a minimum cant think of a better way to use the cavity pull through old to new lovely job.

 

[Pretty Mouth]

The purpose of the diagram was to show the cavity tray which someone said they had never seen, this is all standard building works you guys need to get out more.

I trained and worked as a bricklayer for a few years in the early 2000s, so I know a little bit about this.

Cavity trays and weep holes were installed above openings, and occasionally where insulation didn't run right the way up the cavity wall (eg. it stopped at loft-level). I never once saw anyone install one at ground level, right around the perimeter of the building, as per your diagram, so it certainly wasn't standard practice back then.

Both leaves of the wall had a DPC, typically 150mm above ground, and a weak mix filled the cavity up to ground level, to prevent the earth pushing the walls in. No cavity tray, what would be the point? You think the cavity just fills up with water until it comes out the top?

Perhaps things have changed since then, and they're now mandatory at ground level, but I'd like you to show me a more relevant image or document before I accept your word for it.