Airtight electrical conduits.

jiggins

Hi all.
I want your collective opinions on how to airtight the top of electrical conduits from each light switch/socket where it terminates in the attic. What is best practice in this scenario? Airtight silicone and airtight taping each cable individually?
Thanks for your help.
Jiggins.

BryanF

Google 'air-tight grommets'

jiggins

Thanks Bryan.
Can these be used with conduits chased into the walls?

BryanF

'Air-tight electrical back boxes'

jiggins

Thanks again Bryan. Are these suitable for block built house?

BryanF

jiggins wrote: »

Thanks again Bryan. Are these suitable for block built house?

Yes

But block is porous and needs its own air-tightness consideration

jiggins

Using these airtight back boxes, does each cable have to be individually taped to seal it to the back box or is there an airtight grommet of some sort?

Calahonda52

Is this a DIY self build?

taping cables, while it seems an easier proposition as " there is always" tape on site, is never a good solution as the cables invariably get pulled and the tape gets disturbed.

The other thing you need to decide is where is the A/T layer relative to the cables.

One solution is to use a service cavity outside the A/T layer with proper, multi cable grommets used on the A/T layer and this negates the need for A/T boxes.
However these grommets seem expensive and only the best A/T installers insist on using them. Tape is regarded as being cheap.

It depends what the A/T target is, if any.

As B F noted, your blockwork will need to be made A/T: a common error is to forget to make the chases and back box recesses A/T after the walls are made A/T using sand/cement plaster.

I suppose really what I am saying here is that you need a complete solution thought out rather than the JC, once piece at a time solution
...
Now, up to now my plan went all right
'Til we tried to put it all together one night
And that's when we noticed that something was definitely wrong.

The transmission was a fifty three
And the motor turned out to be a seventy three
And when we tried to put in the bolts all the holes were gone.

So we drilled it out so that it would fit
And with a little bit of help with an adapter kit
We had that engine runnin' just like a song
Now the headlight' was another sight
We had two on the left and one on the right
But when we pulled out the switch all three of 'em come on.

jiggins

It's a self build of sorts - a relation of mine is the builder. I need to have a clear understanding of best practice in order to persuade him to do things as so. I understand now why you should never work with family.
I should explain the current spec a little better. With regard to airtightness of the block work I am not too worried about that as we have used Walltite cavity insulation which should make the walls airtight.
At ceiling level the airtightness membrane is already fitted under the joists. This is then battened and counter battened to create a 75mm service cavity - on investigation this seems too little to successfully terminate the conduits and run the cables into without interfering with the membrane/wall junction. The same is true of fitting downlights as the membrane needs to be patched around each one.
I will now probably drop the ceiling another 50mm or so to allow all electrics to pass through this service cavity ,leaving the membrane untouched.
Airtightness level is set at 2m3/h/m2 at 50pa but we hope to better this considerably.
Any more advice or tips are welcome!
Jiggins.

BarneyMc

jiggins wrote: »

At ceiling level the airtightness membrane is already fitted under the joists. This is then battened and counter battened to create a 75mm service cavity - on investigation this seems too little to successfully terminate the conduits and run the cables into without interfering with the membrane/wall junction. The same is true of fitting downlights as the membrane needs to be patched around each one.
I will now probably drop the ceiling another 50mm or so to allow all electrics to pass through this service cavity ,leaving the membrane untouched.

A 75mm cavity should be loads. On my first floor I had a 45mm service area and that was plenty. With 75mm you can get really shallow down lights that might even fit in here.

jiggins

I'll double check this with builder and electrician Barney. Thank you.

SC024

jiggins wrote: »

It's a self build of sorts - a relation of mine is the builder. I need to have a clear understanding of best practice in order to persuade him to do things as so. I understand now why you should never work with family.
I should explain the current spec a little better. With regard to airtightness of the block work I am not too worried about that as we have used Walltite cavity insulation which should make the walls airtight.
At ceiling level the airtightness membrane is already fitted under the joists. This is then battened and counter battened to create a 75mm service cavity - on investigation this seems too little to successfully terminate the conduits and run the cables into without interfering with the membrane/wall junction. The same is true of fitting downlights as the membrane needs to be patched around each one.
I will now probably drop the ceiling another 50mm or so to allow all electrics to pass through this service cavity ,leaving the membrane untouched.
Airtightness level is set at 2m3/h/m2 at 50pa but we hope to better this considerably.
Any more advice or tips are welcome!
Jiggins.

how will you seal this insulation to your membrane without passing through a porous block? did you building the membrane into the bockwork? how about to the windows? to the floorslab?

jiggins

Ah, I see what you are saying. The builder was adamant that he would still airtight the chases as outlined in other threads - using a pink skim. Windows and floorslab to be taped also.

MicktheMan

jiggins wrote: »

Windows and floorslab to be taped also.

Yes, but taped to what?
The whole idea with airtightness is each elemental barrier is continuously sealed to the next barrier. I cannot see how you could, for instance, seal your floor to your wall air tight barrier if the wall barrier is in the cavity.

jiggins

Windows taped to block work and floor taped to walls. Then walls plastered to make airtight.