Noise 'containing' in new build

[zoothorn]

On 14/04/2020 at 20:09, PeterW said:

Stuff it in - you’re de-rating the cables for 8”

at most which is fine. 

 

Hi Peter.. I just want to be super-sure on this fluff/cables proximity: could you explain what you mean by this ^ post? (I prefer to understand xyz before doing it).

 

I seem to recall 'derating' mentioned before.. but it was complicated.

 

Is there a way to simplify the answer for me (bar 'yes- just stuff it in b*tch!!') ?

 

 

[PeterW]

De-rating cables is when you lower their current carrying capacity as if you wrap a cable in insulation it warms up quicker and therefore as power / amps / heat are directly related you say instead of a wire in insulation carrying say 25 amps, it should only carry a max of 20 amps. 
 

This de-rating is only really relevant when it is for long lengths of cable as they cannot lose this heat elsewhere. As what you are talking about here is a short length of insulation, then it is not relevant. 
 

so .... just stuff it in b**ch..!!! ?

[zoothorn]

9 hours ago, PeterW said:

De-rating cables is when you lower their current carrying capacity as if you wrap a cable in insulation it warms up quicker and therefore as power / amps / heat are directly related you say instead of a wire in insulation carrying say 25 amps, it should only carry a max of 20 amps. 
 

This de-rating is only really relevant when it is for long lengths of cable as they cannot lose this heat elsewhere. As what you are talking about here is a short length of insulation, then it is not relevant. 
 

so .... just stuff it in b**ch..!!! ?

 

But aren't these cables though 'long lengths' ? they're coming from all over the extention > to this congregation area above the door > to all bunch together for the exit thru 2 ft wall.. into main house.

 

I can understand that I'm not 'wrapping them in insulation' (I assume a sheath situation.. but can't picture it).. or.. am I not doing exactly this if I stuff me 'oles guvnor?

[PeterW]

It’s not an issue ... if the whole length was wrapped in insulation then you have to de-rate the cable but you’re not. 
 

Fill the gaps with insulation ... 

[zoothorn]

18 minutes ago, PeterW said:

It’s not an issue ... if the whole length was wrapped in insulation then you have to de-rate the cable but you’re not. 
 

Fill the gaps with insulation ... 

 

Ok I think I understand.. you mean my cables onwards from this stuffed 'junction area' are mostly either sitting ontop the rockwool, clipped to the side of vertical studs with a bit of gap before the rigid PIR (mostly so on the verticals so,).. & even if this congregation/ junction area above door has all the cables squished between joist & the rockwool.. as its only for this small 3ft section, its inconsequential.

 

Am I getting the gist correct here? I'm not quite understanding "wrapped" whether it means an insulation 'sheath' (which not one inch of any cable has anywhere) around a cable, or a full surrounding 'envelope' of rockwool, or whether a combination of rockwool on one side & joist on the other designates it being "wrapped".

[PeterW]

Correct ..! It is about the fibre / thermal insulation not the electrical insulation 

[zoothorn]

43 minutes ago, PeterW said:

Correct ..! It is about the fibre / thermal insulation not the electrical insulation 

 

Ok Peter thanks- will do.

 

[eandg]

On 05/03/2020 at 12:20, Hastings said:

As another poster in another topic pointed out, bear in mind that as far as acoustics go (not thermal) in Mitek's published lab tests Posi Joists benefit by only a 5% (difference of +1dB Rw) in sound transmission when 100mm rockwool is added, compared to when zero insulation fitted between.

 

So maybe don't try and put too much in there.

Interesting info - so what should be used for sound insulation in posi joists then?

[Adsibob]

I tend to use www.soundstop.co.uk for all sound insulation queries and issues. They have products to suit all budgets.

Slightly above mid price, is a sand filled board called an SBx board (https://www.soundstop.co.uk/soundproofing/soundproofing-floors/SBX-boards-solution4.php).

This is really clever because the lattice that holds the sand is in a zig zag shape so it deflects the sound into the board where it hits more sand. 

[Hastings]

On 14/04/2021 at 11:21, eandg said:

Interesting info - so what should be used for sound insulation in posi joists then?

 

I would like to know too. They are not at all suited to adding insulation, particularly since it would be very hard to get insulation into the space within the joists themselves.

[Adsibob]

Why can’t you just pack the spaces with dense mineral wool?

[Hastings]

50mm between flanges seems a good solution.

Edited May 4, 2021 by Hastings