Insulation

[Tobiasisno1]

Hi everybody. I'm still renovating a 100+ years old house (last room now) and have a query on the type of insulation to use. One of the chimney breast alcoves is on the corner of the house and so is very cold-(2 outer walls, solid 9" brickwork). It also has the gas meter and associated pipework, so I have battened it out to cover the pipes and allow for insulation before plaster boarding. I was going to stuff in some fibrous insulation, making it easy to get round the pipe and wiring but I've been told it will eventually sink to the bottom of the space and so I should use the more solid type. Does anyone have any views on this?

Thanks
Keith

 

[PrenticeBoyofDerry]

I'd go with either rockwool,kingspan/celotex type.
The wall will need battening out and a vapour check barrier installed between the insulation and plasterboard. You can buy foil backed plasterboards (duplex) that can be used without vapour check barriers, as the foil serves this purpose.
Be concerned when installing insulation around electric cables, as this reduces the safe current they can carry, it can half quite easy. So never totally surround the cables, unless calcs have been made, that assures it will be safe to do so.

 

[Tobiasisno1]

Thanks PrenticeBoy-I wasn't aware of the point you make about electric cables but I shall not be wrapping them all around with the insulation. Does it make any difference whether the wiring is wall-side or room-side of the insulation?

Keith

 

[mointainwalker]

If possible keep the wiring wall-side as it will be colder and will lose less ( if any ) of its current-carrying capability .

 

[Tobiasisno1]

OK-thanks for help, both

 

[PrenticeBoyofDerry]

If you keep the cable free of of insulation totally it is better, but this could offer cold spots to the wall and that's not what we want so, leave one side of the cable open from insulation.
There's certain calculation that electrician make, to do with de-rating.
This will depend on, where and how cables are installed.
If cable is run through thermal insulation, it can effect the cables insulation as heat that is generated by the current flowing, can not dissipate and this is dangerous and a fire risk.
This can effect the performance by half. ie 2.5mm twin and earth has max current rating of 27 amps, if this cable is totaly surrounded be thermal insulation, it could well lower the current carrying capacity to 13.5 amps.
So if you had a breaker over 13.5 amps protecting this circuit, we have a problem.
Ways to resolve this could be to upgrade your cable or avoid the encasement of insulation.

 

[geraint]

i disagree. it all depends on what insulation you are using.

 

[mointainwalker]

@ Geraint

Why do you disagree ?

What has the type of insulation got to do with anything ?

 

[PrenticeBoyofDerry]

i disagree. it all depends on what insulation you are using.

c ratings is a factor to be applied where the installation conditions differ from those for which values of current-carrying capacity are tabulated in appendix 6 of the on site guide.
Ci for thermal insulation.
Where cables are run in to a space, where thermal insulation, either is or likely to be applied, cables should not be covered in thermal insulation.
If this is not practicable, cable size should be increased if not suitable.
Where cable is totally surrounded be thermal insulation for a distance of 500mm or more a derating factor of 0.50 is applied.
400mm=0.51
200mm=0.63
100mm=0.78
50mm=0.88
That's a guideline given by BS7671:2008 which helps comply to building regulations, HASAW and EAWR.
Nothing about the type insulation used is mentioned.
If you disagree please state why, instead of posting a statement without any support.