Wires in cavity - cavity wall insulation

[siross85]

Hi all.

Last week I decided to take off the old gas flue on the side of our house that was now out of use. When I took it off I noticed there was absolutely no insulation in the cavity whatsoever.

We had the old gas fire removed last year and I ran some wires in the cavity to a wall mounted TV with brush plates at either end. I could see these wires hanging loose when removing the old gas flue. So in other words, there's no trunking protecting the media cables or the power to the spur for the TV.

I also ran 2 x flat ethernet cables and a hybrid HDMI/Fibre cable through the same cavity (at ground level) from the front room to the back room for Sky/Internet duties. I did try to run trunking through here to make it easier to change in the future and protect the cables but I couldn't manage it because of the angle, it was hard enough getting the wires in.

We had a quote for cavity wall insulation last week and I mentioned these wires to the chap and he said it's not a problem as long as they're not power cables and I stupidly forgot that there's a spur for the TV power running in the cavity! Even if the power cable wasn't there, presumably, to protect the power cables and ensure it's possible to actually move or change the cables I'll be best to install some trunking.

I can knock a few bricks out of the external wall (I know exactly where to from bricking up the old gas flue hole). And then install some wide flat trunking such as this, and somehow attaching it to the internal side of the cavity with clips or glue? Would that work?

I'm a bit stumped as to how to protect the cables running between front and back room, does anyone have any ideas?

 

[sparkwright]

I'm not sure I'd worry that much about it, the power socket cable sounds like it is a spur, and won't have much power drawn from it.

If there IS a dramatic effect on the communications cables, it may be easy to replace internally when you next decorate.

Knocking bricks out will lead to noticeable repairs that will drive you crazy.

Once issue is what type of insulation will they install?

You DO NOT want the polystyrene balls.

This reacts with the cables, in that it can breakdown the insulation, and stick to the cable.

The cable sheath can become very sticky.

So you could insist they don't use polystyrene, and go for another material.

However, I would recommend you check on the day what they are going to use, because these insulation companies are generally a bunch of chancers who will fit what THEY want, and don't care because they think no one will ever see there work once it's done.

Alternatively, don't have cavity insulation at all. If you have an older house that wasn't designed to have this fitted, why take the risk?

If you have any damp issues, do NOT install this, as it will later need removing to investigate the problem, particularly if there is rubble in the cavity which is adding to the spread of damp.

 

[crystal ball]

My inlaws had CWI, plagued with damp patches ever since

 

[siross85]

My inlaws had CWI, plagued with damp patches ever since

Oh wow really? That's not good, surely that's not a common fault of CWI?

 

[bernardgreen]

had CWI, plagued with damp patches ever since

a common adverse side effect of injected cavity wall insulation.

 

[sparkwright]

I always think a cavity is there for a REASON.

So why fill it completely with insulation?

Thankfully some new houses are built with sheets of insulation AND a cavity.

The people who supposedly SURVEY old houses for new insulation are a load of clueless salesmen who only care about getting your money.

 

[Harry Bloomfield]

If you have an older house that wasn't designed to have this fitted, why take the risk?

No houses were ever designed to have CWI retrofitted. My home is built on clay, mid 50's, with a slab foundation, brick inner and outer leaf. Nothing to do with the CWI, but my cavities were cleaned out some years before I had CWI installed 25/30 years ago, followed by a new injected damp course. It was blown in as fibre, with holes drilled every metre.

The whole place is noticeably warmer and less expensive to heat. I have had absolutely no damp issues as a result of the CWI, though I do have a tiny amount of damp - just a few inches of internal wall, at the inaccessible back of the downstairs toilet. The other side of the wall is perfectly dry, so my best guess is that the damp course has been bridged by plaster, behind the skirting. Something to fix next time I find a need to rip the toilet out. For now, it is boarded over and disguised by wall-papered ply

 

[Harry Bloomfield]

The people who supposedly SURVEY old houses for new insulation are a load of clueless salesmen who only care about getting your money.

That is very true - best do your own technical research as to whether your home is suitable for CWI installation.

 

[sparkwright]

No houses were ever designed to have CWI retrofitted. My home is built on clay, mid 50's, with a slab foundation, brick inner and outer leaf. Nothing to do with the CWI, but my cavities were cleaned out some years before I had CWI installed 25/30 years ago, followed by a new injected damp course. It was blown in as fibre, with holes drilled every metre.

The whole place is noticeably warmer and less expensive to heat. I have had absolutely no damp issues as a result of the CWI, though I do have a tiny amount of damp - just a few inches of internal wall, at the inaccessible back of the downstairs toilet. The other side of the wall is perfectly dry, so my best guess is that the damp course has been bridged by plaster, behind the skirting. Something to fix next time I find a need to rip the toilet out. For now, it is boarded over and disguised by wall-papered ply

You were quite right to ensure the cavities were thoroughly cleaned out BEFORE the insulation went in, this is instrumental for a trouble-free CWI install.

It is also important to check the pointing is sound, and that there are no other gaps where there shouldn't be.

Some brick is incredibly porous, not good with CWI.

There are some very effective clear solutions for sealing brickwork which really do repell the rain, but these are sometimes criticised for doing more harm than good.

Sometimes it's best not to tamper with things.

 

[siross85]

I'm not sure I'd worry that much about it, the power socket cable sounds like it is a spur, and won't have much power drawn from it.

If there IS a dramatic effect on the communications cables, it may be easy to replace internally when you next decorate.

Knocking bricks out will lead to noticeable repairs that will drive you crazy.

Once issue is what type of insulation will they install?

You DO NOT want the polystyrene balls.

This reacts with the cables, in that it can breakdown the insulation, and stick to the cable.

The cable sheath can become very sticky.

So you could insist they don't use polystyrene, and go for another material.

However, I would recommend you check on the day what they are going to use, because these insulation companies are generally a bunch of chancers who will fit what THEY want, and don't care because they think no one will ever see there work once it's done.

Alternatively, don't have cavity insulation at all. If you have an older house that wasn't designed to have this fitted, why take the risk?

If you have any damp issues, do NOT install this, as it will later need removing to investigate the problem, particularly if there is rubble in the cavity which is adding to the spread of damp.

Yes the power socket is a spur not on the main ring.

I doubt there will be a massive effect on the cables themselves, the main worry would be the issue of changing them in the future, without much knowledge of CWI, is it possible to run wires through it? In other words, would I still be able to pull the wires through and replace after CWI has been installed?

Knocking the bricks out won't be too much of an issue because I had to knock bricks out and replace to brick up the hole left by the flue, this was 4 full bricks in the end. It's enough space to get some trunking in but it sounds like it might not even be worth it.

In terms of the type of insulation, the quote we've received so far has quoted Energystore BAW 18-057-S-A-UK but I'm not sure whether that's related to the type of insulation or not.

I honestly never knew about the risks of damp in houses with CWI, I assumed it was a "no brainer", every day is a school day!

The house was built in the 70s, it's a detached dormer with a damp proof course and lots of air bricks underneath that.

Edit, the quote includes having all the cavities cleared of rubble

 

[bernardgreen]

In the 1960's a neighbour set up as an installer of CWI. If I recall correctly he bought a franchise from the foam supplier. It lasted about a year before he gave up after several disasters. A foam filled pantry and a cracked external wall were just two of them

 

[Harry Bloomfield]

I doubt there will be a massive effect on the cables themselves, the main worry would be the issue of changing them in the future, without much knowledge of CWI, is it possible to run wires through it? In other words, would I still be able to pull the wires through and replace after CWI has been installed?

Keeping in mind the warning about polystyrene dissolving PVC insulation on cables, if it is a loose fill type of insulation, you will have no problems pulling in a new cable using an old or existing one as a draw wire. Chances of your adding a cable without a draw wire, once the CWI is in place are almost nil.

 

[JohnD]

I honestly never knew about the risks of damp in houses with CWI, I assumed it was a "no brainer", every day is a school day!

Edit, the quote includes having all the cavities cleared of rubble

The amount of "talk" greatly exceeds the amount of damp houses.

Now that installers can be forced to remove CWI installed in defective walls at their own expense, they are a lot more careful to look for defects, and have developed experience and techniques over the last 40 years.

I am in an exposed coastal location, my house has soft absorbent buff bricks. My house, and most around it, have been retrofitted with blown water-resistant fibre with good fuel savings and no damp problems, though I have read about people in other areas where it is less suitable. Mine was installed by a contractor for the then Regional Electricity Company, which had a reputation to maintain and enough money to put right any errors.

One of my relations had a house in the West Country with a damp patch. After many years a patch of loose render was found that formed a bubble, and downpipe leak enabled rainwater to collect behind it. Blame the wall defects, not the insulation.

 

[JohnD]

a common adverse side effect of injected cavity wall insulation.

Uncommon.

 

[Harry Bloomfield]

The amount of "talk" greatly exceeds the amount of damp houses.

Now that installers can be forced to remove CWI installed in defective walls at their own expense, they are a lot more careful to look for defects.

It is always the case, they are even concerned such reports will affect covid vaccinations - it only takes a few negative comments, rarely are people vocal who have no problems.