Electric cable run in a room within a room

Hi, can anyone tell me how to run the electric cable for the power sockets in a room within a room structure. I will be filling the stud work with rockwool, do I run the cable horizontal along the noggins and drop down to each socket? I'm not keen to run the cable through holes drilled in the uprights as this interferes with the rockwool slabs i.e. it pushes the slabs against the block wall behind, thus breaking up the air gap. Or can the cable just be run along the floor in the gap between the sole plate and block wall? If this method is used will it have to be put in conduit, this is all assuming that if the cable was run along the block wall behind the air gap it would compromise the effectiveness of the room within a room method when run across the air gap to each socket. Am I worrying too much about a small detail? Any info greatly appreciated. :?:

Hi there am not an expert, but will give you my view as its what I have done, In my mind you are worrying to much about the rockwool touching the blockwork, in actual fact the 'air' space is actually the rockwool and any air space to your block work, you can fill the whole void if you want with rockwool as long as it is not tightly compacted to cause an issue, this way you should run your cables correctly as an electrician would, also bearing in mind that all sparky work has to be done by a fully qualified electrician in the UK now :D Another point is that it is nearly always suggested that your cable is brought into the room at only one point and then surface mount trunking, though I did not go for this method. Also would probably be handy to maybe show some pictures of your build as one of the experts may give you a better answer.

Thanks for your reply, I will be having a qualified sparky to actually wire everything up for me, I'm just doing the cable runs for him to save time. Do you suggest then to run the cable through holes drilled in the studs? The cable enters and exits through one point as you suggest but like yourself I won't be surface mounting any cables or sockets, has this created any issues for you? I'm intending fitting acoustic dry lining boxes for the sockets, are these any good? I'll try and throw some pics up when I get chance. :thu:

If you only have one penetration of the inner-leaf, and plan to distribute from there, and that still needs to go through studs, then that implies that you build your walls using the "inside out" technique (studs facing room, not cavity). Is that correct? - Stuart -

Acoustic boxes may be better I made my studs so that I could use conventional masonry metal back boxes screwed straight on a 4"x2" timber with a single 18mm holed drilled through it to pull the cable through, I then sealed this hole with acoustic caulk, the whole of my airspace is filled with insulation, my live room build then has 15mm OSB and 2 layers of 19mm plasterboard so ends up being thicker than the back boxes.

Soundman2020 wrote:

If you only have one penetration of the inner-leaf, and plan to distribute from there, and that still needs to go through studs, then that implies that you build your walls using the "inside out" technique (studs facing room, not cavity). Is that correct? - Stuart -

The entry and exit point of the cable is through the block "outer" wall, coming from the consumer unit in the room next door, then I have a gap and then a stud-work inner room with rockwool in between studs which will then be covered in sound block plasterboard, so i dont think its the inside out technique as you suggest. Also just to explain that the building is separate from my house, it is a single story block built outbuilding.

The entry and exit point of the cable is through the block "outer" wall, coming from the consumer unit in the room next door, then I have a gap and then a stud-work inner room with rockwool in between studs which will then be covered in sound block plasterboard

OK, got it. So you are not planning on doing the "single penetration" scheme that RJ mentioned. When you follow that scheme, you also have only one penetration of your inner-leaf drywall, and once the wiring is inside the room, you then distribute it from there with surface-mount ducts, plugs, switches, boxes, etc. The ducts can be small and in-obtrusive, and some even come with "peel-and-stick" adhesive backing. Doing it this way means that there is only one point that could compromise your isolation, instead of many points with the way you are planning to do things. Each hole you cut in the wall is destruction of isolation, unless you can replace what you removed, like RJ did with his system. In other words, for every electrical box you mount (switch, outlet, light fitting, junction, etc.), you need to then build a wood or drywall enclosure around the back of that box to maintain the mass, seal and integrity if your inner-leaf. Or you can use putty pads (a.k.a. "putty packs") to accomplish the same purpose. You mold those around the back of each box to replace the lost mass and seal. To my mind, that's a lot of work! And a lot of expense. And a lot of potential points of failure. Surface mount seems expensive at first glance, but when you compare all the pros and cons, it's actually much easier, faster, and really not that much different in cost. But that's my opinion, FWIW! :) Everyone has there own way of doing things, and as long as the end result is that your inner leaf is 100% complete, with the same mass density everywhere, and perfect hermetic seals everywhere, then it doesn't really matter which way you do it.

... which will then be covered in sound block plasterboard,

You could save yourself some money by not using proprietary drywall products. Ordinary 5/8" fire-rated drywall will do the job just as well, a whole lot cheaper... :) Carefully check the only spec that matters: mass per unit area for each product. Then figure out how much each kilogram of mass is costing you. Sound waves don't care about price tags: the only thing they care about is how many kilograms of mass they run into. The cost of the mass is irrelevant... - Stuart -

Surface mount seems expensive at first glance, but when you compare all the pros and cons, it's actually much easier, faster, and really not that much different in cost.

Seems the way to go then. Is there trunking available in anything other than white PVC?

Not sure! I've only ever seen it in white. But if you plan carefully, it can all be covered by your acoustic treatment, so it won't be visible. - Stuart -

The PVC is paintable.