davezawadi (David Stone):

Ah the building is going to be flats, is that why you have the acoustic insulation? 

No - normal residential property (2 story house). Building control are adamant that there has to be some form of insulation in the ceiling void. Architects technician agrees its required to meet regs. I'm not up for the fight to show that it isn't - its a case of picking your battles. I cant find anything in the regs other than 'reasonable provision to reduce sound transmission' which leaves it completely open to interpretation - in this case building control's.


 

Alcomax:

Assuming you may need two circuits, if you did use the existing 2.5 ring, what would that serve at the end of the day?

Edit: looks like a kitchen!

A 2.5 ring on a 20 will work, but not on a large kitchen. Wood supports between joist to have it " clipped" is interesting, but it would still be surrounded by insulation anyhow.  If the existing 2.5 was just two beds and a living room 20 amp would work. With 4mm the trade off 25 amps or 32 amps may not be a big deal. only 7 amps; think the maximum demand of the whole house and the number of circuits,  many rings are not going to be a problem with a 25 amp circuit breaker.

I think I am already at the stage of starting again with 4mm2. There is so much of the existing circuit that would need to be modified with the added complication of junction boxes that I can do without.


There is a natural split down the middle of the kitchen, effectively dividing it into two halves. From the point of view of balancing out the two ring finals better, supplying 1 side of the kitchen, 1 side of the living area (kitchen and living area are open plan 50 sq metre, square dimensions) and 2 bedrooms on one ring final, and the other half on the other seems like the best option. Like you say demand from living area and bedrooms will be relatively low, and the kitchen demand substantially higher.


Looking more carefully I think that reference method 100, if I can clip to wood consistently (it mentions joist but if the noggin is the same size as the joist I cannot see there being any difference with heat transfer):


 

Reference Method 100

Flat Twin and Earth cables - See Table 4D5 for current-carrying capacities:

Installation methods for flat twin and earth cable clipped direct to a wooden joist, or touching the plasterboard ceiling surface, above a plasterboard ceiling with thermal insulation not exceeding 100mm in thickness having a minimum U value of 0.1 W/m²K.


If the insulation is >100mm then its method 101 however this is still >20 Amps per leg if I use 4mm2.


It looks like the solution is my mitre saw, a couple of lengths of 2x6, a reel of 4mm2 T&E  and some graft..........

davezawadi (David Stone):

Ask the Building Inspector about this inter-floor insulation. I have never seen it. Keep asking until he shows you the regulation which requires it.

David, it is all in Part E. Although it seems rather onanistic, there are good reasons for it. For example, at one stage Daughter and her beau had a semi-basement flat in Town. Unfortunately, every little tinkle, splash, and flush from the loo in the landlady's flat above was audible. ?


I note what you say above about acoustic insulation. I have not yet found a value for its U value, but presumably it is a little less than that of thermal insulation. In the meantime, provided that cables are kept to the edges, I think that IM 100# is the best that we can do.

Chris Pearson:

davezawadi (David Stone):

Ask the Building Inspector about this inter-floor insulation. I have never seen it. Keep asking until he shows you the regulation which requires it.

David, it is all in Part E. Although it seems rather onanistic, there are good reasons for it. For example, at one stage Daughter and her beau had a semi-basement flat in Town. Unfortunately, every little tinkle, splash, and flush from the loo in the landlady's flat above was audible. ?


I note what you say above about acoustic insulation. I have not yet found a value for its U value, but presumably it is a little less than that of thermal insulation. In the meantime, provided that cables are kept to the edges, I think that IM 100# is the best that we can do.

Thermal conductivity values are very similar - looking at rockwool - 100mm thermal is 0.044 vs acoustic 0.038 W/mK - and it is on this basis that I am applying the rules for installation in or adjacent to thermal insulation. Im going to run the design past the person issuing the electrical installation certificate before commencing work, but wanted to get it right before submitting it and also for my own piece of mind. I like to work through problems logically and better my understanding through doing so. Thank you for your time in helping with my understanding - I am grateful to all that have contributed to this thread. 

davezawadi (David Stone):

I am beginning to think that something is very wrong here. Thermal insulation between floors of a single dwelling? 


Now the Electrics.

From your description, I assume that the existing property has a single ring serving both floors, in the ceiling void of downstairs. Please advise if this is not the case. You wish to extend it to provide all the power for the extended property. I ask why, I would expect a new circuit at least for the kitchen. Is the ground floor solid? If so run a new circuit in a chase in the walls for downstairs. You will have a plasterer, it is easy to repair. I suggest another circuit for the kitchen only, same installation method, you have to chase the walls anyway so a bit more length is no problem. How will you feed the cooking appliances? It sounds as though the whole conversion/extension is a DIY job. Fine, not a problem, except you will need an Electrical Installation Certificate from a competent source (person) to get the BR completion certificate.


Asking here for a design is OK too, except that we only give advice on the regulations, not a final design. Plenty of ideas here (that is why the forum has members) but ideas are never the complete answer, or the design. Ask the Building Inspector about this inter-floor insulation. I have never seen it. Keep asking until he shows you the regulation which requires it. I have suggested an alternative method, much better than 200mm of Rockwool between floors. This will be thermally better, and much easier on the labour front, both the electrician and labourer and Boss will cost more than you putting up some nice slabs and 1 plasterboard. The loss through the joists makes 100mm useless, so overall only 100mm.


I may have drawn some incorrect conclusions from your data presented. Fair enough, present the real situation, why you want to do A or B is important. I am sure that you will then get the best free advice available.

As I got interrupted I missed the last post. You could do as you say but it is quite a lot of work, reduces the insulation u value of the floor, and will be very difficult to change and test in the future. This is much more than you seem to suggest, it would help if you describe the whole design, including how you intend to cope with partP of the Building Regulations. I trust the BI has told you about that too.

Regards

David CEng.

 

Thanks David for your very detailed reply.


This is acoustic insulation to satisfy part E. There is an argument that it doesnt apply to extensions, but the water here is muddy and both local planning control's ascertion is that it does, as does the independent building control company that I am using for the build (licenced). Being completely honest I am quite pleased that there will be acoustic insulation present as with 3 boys in the house whose version of 'no running in the house' seems to be the complete opposite there may be significant benefit from it!


The extension itself is a project managed professional job. I am only tackling some aspects of it myself - agreed with the team performing the majority of the work. I do not have the skills for the majority of the work, or at least to do it to the standard required and the speed required. We wouldnt cope with the roof half off for 2 months while I did it, but a week is do-able!  I would class myself as a pretty well read DIYer when it comes to both the plumbing and the electrical works. I am reasonably bright, have been through the on site guide and read IET Wiring Regulations: Electric Wiring for Domestic Installers and a couple of other books to understand the theory behind the regulations. Other hobbies involve electronic and microcontroller design mostly for RC model aircraft which involves similar basic principles. I am doing this work because I want to rather than have to - I enjoy the learning and understanding that comes with it even though I will not be using it professionally (Im a surgeon by trade). It would of course be a lot simpler to leave this headache to someone else and pay them for their time, and will indeed be paying someone competent to provide the relevant certificate for building control.  I appreciate that I will not be able to do the job as efficiently as someone with formal training, but with enough care and attention and research I should be able to do the work to an acceptable standard - and if not I will be pulled up on it quite quickly. I hope that helps with where I am coming from on this - not an arrogant 'its easy I can do that' but more a 'I enjoy learning how to do this and it gives me satisfaction to know that I have made some of our home work and work safely'.


So back to your post:

From your description, I assume that the existing property has a single ring serving both floors, in the ceiling void of downstairs. Please advise if this is not the case.


Not quite. The existing property has two 32 Amp ring final circuits on 2.5mmT&E. The first supplies both floors at the front of the property (Study, Kitchen excluding cooker, hallway on GF, hallway on FF, one bedroom). The second supplies both floors at the rear of the property (Living room, two bedrooms).

Lighting is by 2 x 6 Amp radial circuits on 1mm2 T&E, one per floor.

The existing cooker is supplied by a 40 Amp radial on 6mm2 T&E



The extension is at the rear of the property, and two stories. The old kitchen becomes a 'snug' which seems to be the in word for another small living room. No changes need to happen to the front of house ring final to meet new demand (demand will actually reduce).


The old living room becomes the kitchen, the extension the new living room. Upstairs there is the addition of an extra bedroom and ensuite, although the layout changes and existing socket points no longer have a wall to be attached to so will need to be moved.


I am at the point of drawing up the design. preliminary calcs suggest that I could do the whole rear of the house on a single 32 Amp ring final, but in reality I suspect use will push beyond this at times and would rather have the certainty of being well within spec rather than on the edge and risk several thousand pounds of corrective work.


I'm on call tonight, but let me post up the design and calcs once I run through them and then I welcome the scrutiny. Im not expecting people to do this work for me, but a gentle nudge or more if I am going off piste. As a quick summary current plan (in my head) is to replace the rear of property ring final with 2 x ring finals one for each side of the house. cooker will be supplied by a 40 Amp radial as previously but on 10mm2 T&E (this is already in but of course not connected). Part P will be dealt with through the electrician who will be inspecting and the building control company I am using.


Once again thanks for your help

Sparkingchip:

Make it two 16 amp radials with 2.5 twin and earth cables.